Abstract

The objective of this study is to perform a systematic review of published studies that assessed nutrition knowledge in adults, focusing on the methodology and content of these studies. An article search was performed on the Medline, Lilacs, and SciELO databases. The search limits were human studies; English, Portuguese, and Spanish languages; and age (over 19). Inclusion criteria were: cross-sectional studies performed on individuals over 18 years old that assessed the general nutrition knowledge of participants. The methodological quality of the articles was assessed using the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) criteria. The initial search identified 3,623 articles. After reading the titles and the abstracts and applying the exclusion criteria, 25 articles were selected. The results showed that, in most studies, nutrition knowledge was associated with socioeconomic parameters and eating behaviour. Most studies belonged to class B (92%), meeting 50-80% of the STROBE criteria. The studies have revealed a greater tendency to assess the relationship of nutrition knowledge with sociodemographic and economic parameters.

Knowledge; Food and nutrition education; Eating behaviour; Nutritional status

Introduction

Currently, the major causes of mortality worldwide are diseases that could be prevented with proper nutrition, regular physical exercise, and a healthy lifestyle that includes leisure time, stress management, and personal and environmental care¹1. Rodrigues LPF, Roncada MJ. Educação nutricional no Brasil: evolução e descrição de proposta metodológica para escolas. Com Ciências Saúde 2008; 19(4):315-322.; such diseases are called non-communicable diseases (NCDs). In Brazil, NCDs represent a high burden and contribute to the increased health care costs associated with illnesses such as diabetes, hypertension, obesity, and cardiovascular diseases, among other diseases; the existence of long queues for medical appointments at public health units; an increased need for specialized tests and surgeries; and other additional problems²2. Duncan BB, Chor D, Aquino EML, Bensenor IM, Mill JG, Schmidt MI, Lotufo PA, Vigo A, Barreto SM. Doenças Crônicas Não Transmissíveis no Brasil: prioridade para enfrentamento e investigação. Rev Saude Publica 2012; 46(Supl. 1):126-134..

In this sense, one aspect that can improve quality of life is increasing the ability of a population to understand health-related phenomena. The knowledge of health outcomes, in particular regarding NCDs and their risk factors, may be useful in avoiding the onset of a disease and can also influence the search for treatment when there is precise information on the established disease²2. Duncan BB, Chor D, Aquino EML, Bensenor IM, Mill JG, Schmidt MI, Lotufo PA, Vigo A, Barreto SM. Doenças Crônicas Não Transmissíveis no Brasil: prioridade para enfrentamento e investigação. Rev Saude Publica 2012; 46(Supl. 1):126-134.^,33. Vuori I, Paronen O, Oja P. How to develop local physical activity promotion programmes with national support: the Finnish experience. Patient Education and Counseling 1998; 33(Supl. 1):111-120..

Knowledge may be defined as factual and interpretative information that leads to understanding or that is useful in making decisions or informed actions⁴4. Glanz K, Rimer BK, Lewis FM. Health Behavior and Health Education: Theory, Research and Practice. 3rd ed. San Francisco. Calif: Jossey-Bass Publications; 2002.. In cognitive psychology, 2 types of knowledge can be defined: declarative and processual.

Declarative knowledge is defined as the knowledge of facts and things, the knowledge of ‘what is,’ for example, knowing that lemons are a good source of vitamin C or that adequate fruit and vegetable consumption may prevent hypertension. Processual knowledge is the knowledge of how actions are undertaken, for example, how to choose which of 2 snacks is healthier or how to eat a balanced diet⁵5. Worsley A. Nutrition knowledge and food consumption: can nutrition knowledge change food behaviour? Asia Pacific J Clin Nutr 2002; 1(Supl. 3):579-585.^,66. Dickson-Spillmann M, Siegrist M. Consumers’ knowledge of healthy diets and its correlation with dietary behaviour. J Hum Nutr Diet 2011; 24(1):54-60..

Social cognitive theory emphasizes that individual behaviour is determined by the interaction of personal and environmental factors⁷7. Sharma SV, Gernand AD, Day RS. Nutrition knowledge predicts eating behavior of all food groups except fruits and vegetables among adults in the Paso del Norte region: Qué Sabrosa Vida. J Nutr Educ Behav 2008; 40(6):361-368.. In this sense, Motta et al.⁸8. Motta DG, Motta CG, Campos RR. Teorias Psicológicas da Fundamentação do Aconselhamento Nutricional. In: Diez-Garcia RW, Cervato-Mancuso AM, Vannucchi H, organizadores. Mudanças alimentares e educação nutricional. Rio de Janeiro: Guanabara Koogan; 2011. p. 53-65. explain that the personal experiences of each individual encompass cognitive assumptions that will constitute values and beliefs that, based on the reality and experiences lived by each one of us, will become meaningful and predict future events; thus, behaviour and its consequences are dependent on both conscious individual choices and events that occur in the environment in which individuals live. Therefore, social influences from the environment, a lack of motivation, low self-esteem, and societal beliefs and traditions are factors that collaborate to inhibit lifestyle changes, particularly regarding food habits⁸8. Motta DG, Motta CG, Campos RR. Teorias Psicológicas da Fundamentação do Aconselhamento Nutricional. In: Diez-Garcia RW, Cervato-Mancuso AM, Vannucchi H, organizadores. Mudanças alimentares e educação nutricional. Rio de Janeiro: Guanabara Koogan; 2011. p. 53-65..

Based on this premise, educational activities have been developed to disseminate information aimed at changing individual lifestyles, considering that humans build their knowledge day by day based on what they see, hear, feel, and perceive. Humans observe, sort, and select what they consider important for their lives and begin to use what they learn in accordance with their culture. These actions are how humans change themselves and the surrounding world (or resist change)⁹9. Alcides ECA. Promoção das práticas alimentares enquanto ação de Agentes Comunitários de Saúde em bairro da cidade de Salvador, Bahia [dissertação]. Salvador: Universidade Federal da Bahia; 2011.. It is during the performance of their everyday activities that humans improve their actions. According to Paulo Freire¹⁰10. Freire P. Como trabalhar com o povo. São Paulo: Centro de Referência Paulo Freire; 1983.: “…what is essential is to do. To dive into an activity and start learning-relearning, creating-recreating…”.

With respect to food, knowledge on what should be eaten and the awareness of the importance of healthy food habits are the first steps in altering eating behaviour. However, the relationship between what people know and what they do has been considered “very weak”. Knowledge does not stimulate change but instead acts as an important tool when people desire to change, given that knowledge rarely anticipates a behavioural change¹¹11. Chapman KM, Ham JO, Liesen P, Winter L. Applying behavioral models to dietary education of elderly diabetic patients. J Nutr Educ Behav 1995; 27(2):75-79.. From this perspective, nutrition knowledge (NK) may be defined as the individual cognitive process related to information on food and nutrition¹²12. Axelson ML, Brinberg D. The measurement and conceptualization of nutrition knowledge. J Nutr Educ Behav 1992; 24(5):239-246., and it may have something to do with food selection¹³13. Scagliusi FB, Polacow VO, Cordás TA, Coelho D, Alvarenga M, Philippi ST, Lancha Júnior AH. Tradução, adaptação e avaliação psicométrica da Escala de Conhecimento Nutricional do National Health Interview Survey Cancer Epidemiology. Rev Nutr 2006; 19(4):425-436. and success in NCD prevention¹⁴14. Després JP, Lamarche B. Low intensity endurance exercise training, plasma lipoporotein and the risk of coronary heart disease. J Intern Med 1994; 236(1):7-22..

Triches and Giugliani¹⁵15. Triches RM, Giugliani ERJ. Obesidade, práticas alimentares e conhecimentos de nutrição em escolares. Rev Saude Publica 2005; 39(4):541-547. state that individual NK may favour healthy food consumption and thus promote changes in food habits that may reduce the risks of developing NCDs. In a systematic review on the association between NK and dietary intake in adults based on cross-sectional and quasi-experimental, randomised clinical trials, Spronk et al.¹⁶16. Spronk I, Kullen C, Burdon C, O’Connor H. Relationship between nutrition knowledge and dietary intake. Br J Nutr 2014; 111(10):1713-1726. concluded that most studies present a weak association between NK and food consumption. However, according to the knowledge-attitude-behaviour model, knowledge might not produce positive and significant changes in eating behaviour, and it is essential to have a motivation or stimulus to make change occur¹⁷17. Aldrich L. Consumer use of information: implications for food policy. Washington: USDA; 1999. An Economic Research Service Report, USDA, Agricultural Handbook, Report D.C.; n. 715..

Considering all of the issue noted above, NK assessment is a relevant topic because the level of NK might be associated with eating behaviour, can promote changes in inadequate food habits, and promotes alterations in nutritional status. The objective of this study is to systematically review the literature on studies assessing the level of nutrition knowledge in adults, focusing on the methodology and content of these studies.

Methods

This study is a systematic literature review. The question this review aimed to answer is the following: ‘What methods are being used in cross-sectional observational studies to assess the level of general NK in adults?’

Search strategy

Relevant articles were identified in April 2013 by performing a search on three electronic databases: Medical Literature Library of Medicine (Medline) via PubMed; Scientific Electronic Library (SciELO); and Latin-American and Caribbean Literature (Literatura Latino-Americana e do Caribe - Lilacs) via Virtual Health Library (Biblioteca Virtual em Saúde - BVS). Using PubMed as reference, the article search was conducted using the limits ‘humans’; ‘age’ – applying the three available filters ‘Adult: 19+ years, Young Adult: 19-24 years, and Adult:19-44 years’; and ‘language’ – English, Portuguese, and Spanish. When necessary, these limits were adapted to resources available in other databases.

The terms used for the article search were identified in Health Sciences Descriptors (Descritores em Ciências da Saúde - DECS). The following keywords were used: nutritional status, body mass index, nutrition assessment, food habits, food consumption, knowledge and health knowledge, attitudes, and practice. The search strategy was organized according to the characteristics of each database. The logical operators OR and AND were used to combine the terms used for the article search.

Eligibility criteria

Eligible studies met the following criteria: cross-sectional observational study; participants aged > 18 years, regardless of gender, country, ethnicity, and socioeconomic status; and description of the methodology used to assess the level of general NK.

The following were excluded: review articles; case-control, cohort, ecological, and interventional epidemiological studies; studies with children and adolescents; duplicate studies; exclusively qualitative studies; studies on the development, validation, and reproducibility of NK questionnaires; studies that assessed specific aspects of nutrition and food knowledge such as only fruits, vegetables, fat, fibres; and articles that did not address NK.

Article selection

Two authors independently reviewed the title and abstract of the articles identified by the initial search strategy, using the predefined inclusion and exclusion criteria. Disagreements that occurred during the selection step were settled by consensus; if consensus was not reached, more experienced researchers were consulted.

Each study was described based on the following information: year of publication; journal and year in which the study was performed; study location; population; sample size; objective; anthropometric, dietary, sociodemographic, and economic variables; the tools used to assess NK, including how the tools were used; classification and assessment criteria; and associations between NK and the analysed variables.

Methodological quality assessment

Eligible articles were reviewed by two authors according to the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology)¹⁸18. Von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. BMJ 2007; 335(7624):806-808. criteria. As in Mendes et al.¹⁹19. Mendes KG, Theodoro H, Rodrigues AD, Olinto MTA. Prevalência de síndrome metabólica e seus componentes na transição menopáusica: uma revisão sistemática. Cad Saude Publica 2012; 28(8):1423-1437., each of the 22 criteria was given a score of 0 (meets the criterion) to 1 (does not meet the criterion). After assessing all of the criteria, each article received a score from 0 to 22 from each reviewer. The final score was obtained by calculating the mean score of both reviewers. The manuscripts were ordinally ranked according to their final score. The global score was converted into a percentage to assess article quality and to classify the articles into three categories, according to Mataratzis et al.²⁰20. Mataratzis PSR, Accioly E, Padilha PC. Deficiências de micronutrientes em crianças e adolescentes com anemia falciforme: uma revisão sistemática. Rev Bras Hematol Hemoter 2010; 32(3):247-256.: A – study meets more than 80% of the STROBE criteria; B – study meets 50-80% of the STROBE criteria; and C – study meets less than 50% of the STROBE criteria. In case of disagreement, two other researchers were consulted.

Results

A total of 3,623 articles were identified. Following the analysis of titles and abstracts and the application of exclusion criteria, 25 studies were selected for inclusion in this systematic review, as shown in Figure 1. Regarding the assessment of methodological quality using the STROBE¹⁸18. Von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. BMJ 2007; 335(7624):806-808. criteria, none of the studies analysed was classified as quality C; 8% (n = 2) and 92% (n = 23) were classified as quality A and B, respectively (Table 1).

The articles reviewed in this study are presented in Charts 1 and 2 by study year/location, sample description, analysed variables, objectives, summary of the tools used for NK assessment and classification, and associations with NK.

Study year/location

Articles in this area began to be published in 2000 and continued in low numbers until 2003 (a mean number of 1 article per year), returning in 2005 with the studies by Lin and Lee²⁸28. Lin W, Lee YW. Nutrition knowledge, attitudes and dietary restriction behaviour of Taiwanese elderly. Asia Pac J Clin Nutr 2005; 14(3):221-229. and Schaller and James³²32. Schaller C, James EL. The nutritional knowledge of Australian nurses. Nurse Educ Today 2005; 25(5):405-412.. From this year on, the mean number of published articles increased to three articles/year. The studies were performed from 1999 to 2015. However, 36% of the authors (n = 9) did not report the year of the study. Interestingly, the study by Mimiran et al.⁴³43. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240. was performed in 1999, but there is a difference of 11 years between the year in which the study was performed and the year of publication.

The journals with the highest number of published articles were Asia Pacific Journal of Clinical Nutrition and Journal of The American Dietetic Association, with three articles each (12%).

NK assessment studies were performed on five continents. Brazil is the country with the highest number of studies (n = 4; 16%), followed by the US and Australia, each with 12% (n = 3) of the articles.

Sample description

In most studies, the population was composed of adults of both genders, aged from 18 to 75 years old; the exceptions are the studies by Zawila et al.³⁵35. Zawila LG, Steib C-SM, Hoogenboom B. The Female Collegiate Cross-Country Runner: Nutritional Knowledge and Attitudes. J Athl Train 2003; 38(1):67-74., Freitas et al.²⁶26. Freitas ECB, Alvarenga MS, Scagliusi FB. Avaliação do conhecimento nutricional e frequência de ingestão de grupos alimentares em vegetarianos e não vegetarianos. Rev Bras Nutr Clin 2006; 21(4):267-272., Pon et al.²⁵25. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399., Holdsworth et al.³³33. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981., Nuss et al.²³23. Nuss H, Freeland-graves J, Clarke K, Klohe-lehman D, Milani TJ. Greater Nutrition Knowledge Is Associated with Lower 1-Year Postpartum Weight Retention in Low-Income Women. J Am Diet Assoc 2007; 107(10):1801-1806., De Vriendt et al.⁴⁰40. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792., Castro et al.³⁰30. Castro NMG, Dáttilo M, Lopes LC. Avaliação do conhecimento nutricional de mulheres fisicamente ativas e sua associação com o estado nutricional. Rev Bras Ciênc Esporte 2010; 32(1):161-172., Galindo Gomes et al.⁴¹41. Galindo Gómez C, Juárez Martínez L, Shamah Levy T, García Guerra A, Avila Curiel A, Quiroz Aguilar MA. Nutritional knowledge and its association with overweight and obesity in Mexican women with low socioeconomic level. Arch Latinoam Nutr 2011; 61(4):396-405. and McLeod et al.⁴²42. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704., which were performed with women only. These studies correspond to 36% (n = 9) of the reviewed articles.

The smallest sample size was of 21, and the largest sample was composed of 2,027 participants. It is noteworthy that these samples were obtained almost entirely by convenience.

Analysed variables and objectives

Most studies did not analyse dietary, anthropometric, socioeconomic, and demographic variables simultaneously; only 32% of the studies did so²⁵25. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399.^,2626. Freitas ECB, Alvarenga MS, Scagliusi FB. Avaliação do conhecimento nutricional e frequência de ingestão de grupos alimentares em vegetarianos e não vegetarianos. Rev Bras Nutr Clin 2006; 21(4):267-272.^,2929. Kolodinsky J, Harvey-Berino JR, Berlin L, Johnson RK, Reynolds TW. Knowledge of current dietary guidelines and food choice by college students: better eaters have higher knowledge of dietary guidance. J Am Diet Assoc 2007; 107(8):1409-1413.^,3939. Al Riyami A, Al Hadabi S, Abd El Aty MA, Al Kharusi H, Morsi M, Jaju S. Nutrition knowledge, beliefs and dietary habits among elderly people in Nizwa, Oman: implications for policy. East Mediterr Health J 2010; 16(8):859-867.

40. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792.

41. Galindo Gómez C, Juárez Martínez L, Shamah Levy T, García Guerra A, Avila Curiel A, Quiroz Aguilar MA. Nutritional knowledge and its association with overweight and obesity in Mexican women with low socioeconomic level. Arch Latinoam Nutr 2011; 61(4):396-405.

42. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.^-4343. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240.. However, sociodemographic and economic data were assessed by all studies. Of these, 25% (n = 6) assessed only these data, with the most frequent variables analysed being age, gender, educational level, occupation, income, marital status, number of children, and ethnicity. Regarding nutritional assessment, the most studied variables were as follows: weight, height, body mass index (BMI), waist circumference (WC) and hip circumference (HC), and food consumption. BMI was assessed in all articles that analysed anthropometric data (n = 14). However, WC and HC were analysed simultaneously only by Pon et al.²⁵25. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399. and Mirmiran et al.⁴³43. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240..

The food consumption assessment tool used in 61.54% (n = 8) of the 13 studies that analysed diet was a food frequency questionnaire (FFQ)⁶6. Dickson-Spillmann M, Siegrist M. Consumers’ knowledge of healthy diets and its correlation with dietary behaviour. J Hum Nutr Diet 2011; 24(1):54-60.^,2525. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399.^,2626. Freitas ECB, Alvarenga MS, Scagliusi FB. Avaliação do conhecimento nutricional e frequência de ingestão de grupos alimentares em vegetarianos e não vegetarianos. Rev Bras Nutr Clin 2006; 21(4):267-272.^,3636. Gámbaro A, Raggio L, Dauber C, Claudia Ellis A, Toribio Z. Nutritional knowledge and consumption frequency of foods--a case study. Arch Latinoam Nutr 2011; 61(3):308-315.^,3939. Al Riyami A, Al Hadabi S, Abd El Aty MA, Al Kharusi H, Morsi M, Jaju S. Nutrition knowledge, beliefs and dietary habits among elderly people in Nizwa, Oman: implications for policy. East Mediterr Health J 2010; 16(8):859-867.^,4242. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.

43. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240.^-4444. Kresić G, Kendel Jovanović G, Pavicić Zezel S, Cvijanović O, Ivezić G. The effect of nutrition knowledge on dietary intake among Croatian university students. Coll Antropol 2009; 33(4):1047-1056..

In general, the objective of the studies was to describe and/or assess NK and to correlate it with nutritional status, eating behaviour, or economic and sociodemographic variables. Although, in 40% of the studies²⁵25. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399.^,2626. Freitas ECB, Alvarenga MS, Scagliusi FB. Avaliação do conhecimento nutricional e frequência de ingestão de grupos alimentares em vegetarianos e não vegetarianos. Rev Bras Nutr Clin 2006; 21(4):267-272.^,3131. Lin W, Hang C-M, Yang H-C, Hung M-H. 2005-2008 Nutrition and Health Survey in Taiwan: the nutrition knowledge, attitude and behavior of 19-64 year old adults. Asia Pac J Clin Nutr 2011; 20(2):309-318.

32. Schaller C, James EL. The nutritional knowledge of Australian nurses. Nurse Educ Today 2005; 25(5):405-412.^-3333. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981.^,3535. Zawila LG, Steib C-SM, Hoogenboom B. The Female Collegiate Cross-Country Runner: Nutritional Knowledge and Attitudes. J Athl Train 2003; 38(1):67-74.

36. Gámbaro A, Raggio L, Dauber C, Claudia Ellis A, Toribio Z. Nutritional knowledge and consumption frequency of foods--a case study. Arch Latinoam Nutr 2011; 61(3):308-315.

37. Carrillo E, Varela P, Fiszman S. Influence of nutritional knowledge on the use and interpretation of Spanish nutritional food labels. J Food Sci 2012; 77(1):1-8.^-3838. Hendrie GA, Coveney J, Cox D. Exploring nutrition knowledge and the demographic variation in knowledge levels in an Australian community sample. Public Health Nutr 2008; 11(12):1365-1371.^,4343. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240., the authors did not state in the article that one of the objectives was to test the existence of associations, most of them presented data on this matter in the results section.

Nutrition knowledge assessment tools

A total of 44% (n = 11) of the studies used questionnaires specifically designed for their own investigations⁶6. Dickson-Spillmann M, Siegrist M. Consumers’ knowledge of healthy diets and its correlation with dietary behaviour. J Hum Nutr Diet 2011; 24(1):54-60.^,2323. Nuss H, Freeland-graves J, Clarke K, Klohe-lehman D, Milani TJ. Greater Nutrition Knowledge Is Associated with Lower 1-Year Postpartum Weight Retention in Low-Income Women. J Am Diet Assoc 2007; 107(10):1801-1806.^,2525. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399.^,2828. Lin W, Lee YW. Nutrition knowledge, attitudes and dietary restriction behaviour of Taiwanese elderly. Asia Pac J Clin Nutr 2005; 14(3):221-229.^,3131. Lin W, Hang C-M, Yang H-C, Hung M-H. 2005-2008 Nutrition and Health Survey in Taiwan: the nutrition knowledge, attitude and behavior of 19-64 year old adults. Asia Pac J Clin Nutr 2011; 20(2):309-318.^,3333. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981.^,3939. Al Riyami A, Al Hadabi S, Abd El Aty MA, Al Kharusi H, Morsi M, Jaju S. Nutrition knowledge, beliefs and dietary habits among elderly people in Nizwa, Oman: implications for policy. East Mediterr Health J 2010; 16(8):859-867.^,4141. Galindo Gómez C, Juárez Martínez L, Shamah Levy T, García Guerra A, Avila Curiel A, Quiroz Aguilar MA. Nutritional knowledge and its association with overweight and obesity in Mexican women with low socioeconomic level. Arch Latinoam Nutr 2011; 61(4):396-405.

42. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.^-4343. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240.. In general, these assessment questionnaires addressed nutrients (carbohydrates, lipids, proteins, vitamins, minerals, and fibres); the health benefits of food; the diet-disease relationship (obesity, cardiovascular disease, and non-communicable diseases in general); fruits and vegetables; salt; and the food pyramid. The Nutritional Knowledge Questionnaire (NKQ)⁴⁵45. Parmenter K, Wardle J. Development of a general nutrition knowledge questionnaire for adults. Eur J Clin Nutr 1999; 53(4):298-308. was used by 32% of the studies (n = 8); The NKQ was developed and validated for use in the English-speaking population, aged 18 or over, and assesses knowledge on dietary recommendations, nutrient sources, daily food choices, and the diet-disease relationship. The Harnack et al.⁴⁶46. Harnack L, Block G, Subar A, Lane S, Brand R. Association of cancer prevention-related nutrition knowledge, beliefs, and attitudes to cancer prevention dietary behavior. J Am Diet Assoc 1997; 97(9):957-965. NK scale, translated into and validated for Portuguese by Scagliusi et al.¹³13. Scagliusi FB, Polacow VO, Cordás TA, Coelho D, Alvarenga M, Philippi ST, Lancha Júnior AH. Tradução, adaptação e avaliação psicométrica da Escala de Conhecimento Nutricional do National Health Interview Survey Cancer Epidemiology. Rev Nutr 2006; 19(4):425-436., was used in 16% (n = 4) of the articles²¹21. Oliveira FL, Russo FM, Menegatti I, Toya MM, Stulbach E, Garcia LS, Peron AN, Dattilo M. Avaliação do conhecimento nutricional de atletas de judô. Lécturas Educación Física y Deportes [periódico na Internet]. 2009 [acessado 2015 Mar 06]; 14(138). Disponível em: http://www.efdeportes.com/efd138/conhecimento-nutricional-de-atletas-de-judo.htm
http://www.efdeportes.com/efd138/conheci... ^,2626. Freitas ECB, Alvarenga MS, Scagliusi FB. Avaliação do conhecimento nutricional e frequência de ingestão de grupos alimentares em vegetarianos e não vegetarianos. Rev Bras Nutr Clin 2006; 21(4):267-272.^,2727. Dattilo M, Furlanetto P, Kuroda AP, Nicastro H, Coimbra PCFC, Simony RF. Conhecimento nutricional e sua associação com o índice de massa corporal. Nutrire Rev Soc Bras Aliment Nutr 2009; 34(1):75-84.^,3030. Castro NMG, Dáttilo M, Lopes LC. Avaliação do conhecimento nutricional de mulheres fisicamente ativas e sua associação com o estado nutricional. Rev Bras Ciênc Esporte 2010; 32(1):161-172.; this scale assesses knowledge on the diet-disease relationship, the amount of fibres and lipids in food, and the recommendations of fruit and vegetable consumption. Schaller and James³²32. Schaller C, James EL. The nutritional knowledge of Australian nurses. Nurse Educ Today 2005; 25(5):405-412. studied nurses and used the questionnaire designed by Henderson Sabry et al.⁴⁷47. Henderson Sabry J, Hedley M, Kirstine M. Nutrition applications in public health nursing: a survey of needs and preferences of public health nurses for continuing education in nutrition. Can J Public Health 1987; 78(1):51-56. specifically for these professionals. Kolodinsky et al.²⁹29. Kolodinsky J, Harvey-Berino JR, Berlin L, Johnson RK, Reynolds TW. Knowledge of current dietary guidelines and food choice by college students: better eaters have higher knowledge of dietary guidance. J Am Diet Assoc 2007; 107(8):1409-1413. used the questionnaire based on the MyPyramid Food Guidance System⁴⁸48. US Department of Agriculture, Center for Nutrition Policy and Promotion. MyPyramid Food Guidance System Education Framework. [cited 2015 Feb 15]. Available from: http://www.choosemyplate.gov/food-groups/downloads/MyPyramid_education_ framework.pdf
http://www.choosemyplate.gov/food-groups... and on the Diet and Heath Knowledge Survey from the US Department of Agriculture⁴⁹49. US Department of Agriculture, Agricultural Research Service. What we eat in America 1994-1996 Continuing Survey of Food Intake by Individuals and the1994-96 Diet and Health Knowledge Survey. [cited 2015 Jan 16]. Available from: http://www.ars.usda.gov/SP2UserFiles/Place/12355000/pdf/dhks.pdf
http://www.ars.usda.gov/SP2UserFiles/Pla... ; it addresses knowledge on energy, total fat, saturated and trans, added sugars, fibres, and the importance of keeping a healthy weight and of eating different fruits and vegetables.

How the answers to the questionnaires were assessed is not stated in 44% (n = 11) of the articles. In 28% (n = 7), only the maximum score that could be reached if all questions were answered correctly was given²²22. O’Brien G, Davies M. Nutrition knowledge and body mass index. Health Educ Res [serial on the Internet]. 2007 [cited 2015 Mar 21]; 22(4):[about 5p.]. Available from: http://her.oxfordjournals.org/content/22/4/571.
http://her.oxfordjournals.org/content/22... ^,3232. Schaller C, James EL. The nutritional knowledge of Australian nurses. Nurse Educ Today 2005; 25(5):405-412.^,3636. Gámbaro A, Raggio L, Dauber C, Claudia Ellis A, Toribio Z. Nutritional knowledge and consumption frequency of foods--a case study. Arch Latinoam Nutr 2011; 61(3):308-315.^,3838. Hendrie GA, Coveney J, Cox D. Exploring nutrition knowledge and the demographic variation in knowledge levels in an Australian community sample. Public Health Nutr 2008; 11(12):1365-1371.^,4040. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792.^,4242. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.^,4444. Kresić G, Kendel Jovanović G, Pavicić Zezel S, Cvijanović O, Ivezić G. The effect of nutrition knowledge on dietary intake among Croatian university students. Coll Antropol 2009; 33(4):1047-1056.. The remaining 28% classified NK as low, poor, or weak (0-9 points); moderate or medium (7 to 10 points); and high (above 10). These scores varied according to the methodology used by the authors, with different points in the classification scores.

NK Associations

Associations between NK and socioeconomic and demographic variables (age, gender, educational level, and family income) were identified in 64% of the studies. However, Holdsworth et al.³³33. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981. did not find a relationship between NK and education. By contrast, BMI, which was assessed in 56% of the studies (n = 14), was associated with NK in 42.8% of the studies, and such association could be positive²⁷27. Dattilo M, Furlanetto P, Kuroda AP, Nicastro H, Coimbra PCFC, Simony RF. Conhecimento nutricional e sua associação com o índice de massa corporal. Nutrire Rev Soc Bras Aliment Nutr 2009; 34(1):75-84.^,4141. Galindo Gómez C, Juárez Martínez L, Shamah Levy T, García Guerra A, Avila Curiel A, Quiroz Aguilar MA. Nutritional knowledge and its association with overweight and obesity in Mexican women with low socioeconomic level. Arch Latinoam Nutr 2011; 61(4):396-405., negative⁴⁰40. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792., and not present²²22. O’Brien G, Davies M. Nutrition knowledge and body mass index. Health Educ Res [serial on the Internet]. 2007 [cited 2015 Mar 21]; 22(4):[about 5p.]. Available from: http://her.oxfordjournals.org/content/22/4/571.
http://her.oxfordjournals.org/content/22... ^,3333. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981.; in Nuss et al.²³23. Nuss H, Freeland-graves J, Clarke K, Klohe-lehman D, Milani TJ. Greater Nutrition Knowledge Is Associated with Lower 1-Year Postpartum Weight Retention in Low-Income Women. J Am Diet Assoc 2007; 107(10):1801-1806., women with less than 5% of weight retention (compared to pre-pregnancy weight, assessed by BMI) during the first year postpartum had better NK.

Associations were found between NK and several positive aspects of diet (n = 10): healthy eating²⁹29. Kolodinsky J, Harvey-Berino JR, Berlin L, Johnson RK, Reynolds TW. Knowledge of current dietary guidelines and food choice by college students: better eaters have higher knowledge of dietary guidance. J Am Diet Assoc 2007; 107(8):1409-1413.^,3434. Wardle J, Parmenter K, Waller J. Nutrition knowledge and food intake. Appetite 2000; 34(3):269-275.; increased fruit and vegetable consumption ⁶6. Dickson-Spillmann M, Siegrist M. Consumers’ knowledge of healthy diets and its correlation with dietary behaviour. J Hum Nutr Diet 2011; 24(1):54-60.^,3636. Gámbaro A, Raggio L, Dauber C, Claudia Ellis A, Toribio Z. Nutritional knowledge and consumption frequency of foods--a case study. Arch Latinoam Nutr 2011; 61(3):308-315.^,4040. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792.; and a low intake of simple sugars, fat, and salt, among others²⁸28. Lin W, Lee YW. Nutrition knowledge, attitudes and dietary restriction behaviour of Taiwanese elderly. Asia Pac J Clin Nutr 2005; 14(3):221-229.^,3636. Gámbaro A, Raggio L, Dauber C, Claudia Ellis A, Toribio Z. Nutritional knowledge and consumption frequency of foods--a case study. Arch Latinoam Nutr 2011; 61(3):308-315..

In light of the results presented in Charts 1 and 2, some conclusions, according to the population studied, were: for women, the most important NK determinants were educational level, age, and occupation⁴⁰40. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792.; nutritional education is important for the elderly, and the development of nutritional education programmes must consider the low educational levels of elderly people²⁸28. Lin W, Lee YW. Nutrition knowledge, attitudes and dietary restriction behaviour of Taiwanese elderly. Asia Pac J Clin Nutr 2005; 14(3):221-229.; NK is an important target for health education and has the potential to contribute to a better dietary quality³⁴34. Wardle J, Parmenter K, Waller J. Nutrition knowledge and food intake. Appetite 2000; 34(3):269-275.; the knowledge of food, nutritional properties, and recommendations on the size and frequency of consumption must be the primary goals of nutritional education programmes throughout the life of individuals³⁶36. Gámbaro A, Raggio L, Dauber C, Claudia Ellis A, Toribio Z. Nutritional knowledge and consumption frequency of foods--a case study. Arch Latinoam Nutr 2011; 61(3):308-315..

Discussion

This investigation is the first systematic review on cross-sectional studies that assessed the level of general NK in adults; however, similarly to Sarno et al.⁵⁰50. Sarno F, Jaime PC, Ferreira SRG, Monteiro CA. Consumo de sódio e síndrome metabólica: uma revisão sistemática. Arq Bras Endocrinol Metab 2009; 53(5):608-616., it was not possible to perform a meta-analysis due to the heterogeneity of the populations, methods, and tools used in these studies.

The identification of 25 articles that met the inclusion criteria demonstrates that NK assessment has been gaining attention among researchers worldwide. Although no year of publication filter has been used to include all of the studies on the topic of interest, publications in this field began recently (year 2000), and the number of articles/year has been increasing since 2005, reaching a mean number of three articles/year, which also demonstrates the current importance of this topic. According to Verbeek et al.⁵¹51. Verbeek A, Debackere K, Luwel M, Zimmermann E. Measuring progress and evolution in science and technology – I: The multiple uses of bibliometric indicators. Int. J Manag Rev 2002; 4(2):179-211., the number of published articles can be used to quantify scientific progress and evolution.

In the assessment of the STROBE criteria, all of the selected articles presented percentages higher than 50%, which corresponded to a classification of A or B. In the studies by Mirmiram et al.⁴³43. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240. and Kresić et al.⁴⁴44. Kresić G, Kendel Jovanović G, Pavicić Zezel S, Cvijanović O, Ivezić G. The effect of nutrition knowledge on dietary intake among Croatian university students. Coll Antropol 2009; 33(4):1047-1056., which scored 80% and belonged to the STROBE A category, NK was associated with age (p < 0.01), educational level (p < 0.01), and gender (p < 0.05) and with the consumption of food servings in accordance with that recommended by the food pyramid (p < 0.01), respectively.

The fact that studies were performed in countries from five continents; that sample size varied widely among the studies that almost no articles assesses dietary, anthropometric, sociodemographic, and economic variables simultaneously; and that the methods used were different limits our discussion of the results by making comparisons between studies more difficult. Silveira and Santos⁵²52. Silveira DS, Santos IS. Adequação do pré-natal e peso ao nascer: uma revisão sistemática. Cad Saude Publica 2004; 20(5):1160-1168. and Barros et al.⁵³53. Barros DC, Saunders C, Leal MC. Avaliação nutricional antropométrica de gestantes brasileiras: uma revisão sistemática. Rev Bras Saude Mater Infant 2008; 8(4):363-376. have also noted the difficulty of not being able to establish comparisons between results that use different methods. In addition, each article cites its own limitations, which include the following: the use of NK questionnaire not validated for that specific population³⁵35. Zawila LG, Steib C-SM, Hoogenboom B. The Female Collegiate Cross-Country Runner: Nutritional Knowledge and Attitudes. J Athl Train 2003; 38(1):67-74.^,4141. Galindo Gómez C, Juárez Martínez L, Shamah Levy T, García Guerra A, Avila Curiel A, Quiroz Aguilar MA. Nutritional knowledge and its association with overweight and obesity in Mexican women with low socioeconomic level. Arch Latinoam Nutr 2011; 61(4):396-405.; self-reported data²⁹29. Kolodinsky J, Harvey-Berino JR, Berlin L, Johnson RK, Reynolds TW. Knowledge of current dietary guidelines and food choice by college students: better eaters have higher knowledge of dietary guidance. J Am Diet Assoc 2007; 107(8):1409-1413.^,4242. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.; the non-validation of NK questionnaire scoring methods⁴²42. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.; the sampling technique used²²22. O’Brien G, Davies M. Nutrition knowledge and body mass index. Health Educ Res [serial on the Internet]. 2007 [cited 2015 Mar 21]; 22(4):[about 5p.]. Available from: http://her.oxfordjournals.org/content/22/4/571.
http://her.oxfordjournals.org/content/22... ^,3333. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981.; the fact that some participants participated in health and nutrition educational programmes^27;; and the sample size – the use of a small sample²⁷27. Dattilo M, Furlanetto P, Kuroda AP, Nicastro H, Coimbra PCFC, Simony RF. Conhecimento nutricional e sua associação com o índice de massa corporal. Nutrire Rev Soc Bras Aliment Nutr 2009; 34(1):75-84.^,2929. Kolodinsky J, Harvey-Berino JR, Berlin L, Johnson RK, Reynolds TW. Knowledge of current dietary guidelines and food choice by college students: better eaters have higher knowledge of dietary guidance. J Am Diet Assoc 2007; 107(8):1409-1413.; regarding this last limitation, Schaller and James³²32. Schaller C, James EL. The nutritional knowledge of Australian nurses. Nurse Educ Today 2005; 25(5):405-412. state that, although the sample size was sufficient to estimate NK prevalence with proper statistic power, it was inadequate to perform regression analysis. Thus, the limitations of this review, together with those presented by each article, have hampered the compilation and comparison of results; thus, it is important to perform studies on this subject that use tools and methods that are validated and/or adequate to each study.

The analysis of the sociodemographic and economic variables performed by all of the authors indicates that these phenomena are an important and relevant aspect for NK and the general well-being of participants. One study performed in three low-income neighbourhoods of Fortaleza (state of Ceará, Brazil), conducted by the World Bank, assessed the social risk of poverty and found that the risk factors were low educational and social capital levels, family breakdown, and early pregnancy, among others⁵⁴54. Verner D, Alda E. Youth At Risk, Social Exclusion, and Intergenerational Poverty Dynamics: A New Survey Instrument with Application to Brazil. World Bank Policy Research Working Paper 3296. [Internet]. 2004. 46p. [cited 2015 Feb 06]. Available from: http://elibrary.worldbank.org/doi/pdf/10.1596/1813-9450-3296.
http://elibrary.worldbank.org/doi/pdf/10... . Poverty exists when part of a population cannot make a sufficient income to have sustainable access to the basic resources (water, health, education, food, housing, income, and citizenship) that ensure a good quality of life. Low socioeconomic status interferes with healthcare and food habits because, by affecting the family structure, life and food quality are also affected⁵⁴54. Verner D, Alda E. Youth At Risk, Social Exclusion, and Intergenerational Poverty Dynamics: A New Survey Instrument with Application to Brazil. World Bank Policy Research Working Paper 3296. [Internet]. 2004. 46p. [cited 2015 Feb 06]. Available from: http://elibrary.worldbank.org/doi/pdf/10.1596/1813-9450-3296.
http://elibrary.worldbank.org/doi/pdf/10...

55. Gomes MA, Pereira MLD. Família em situação de vulnerabilidade social: uma questão de políticas públicas. Cien Saude Colet 2005; 10(2):357-363.^-5656. Diez-Garcia RW. Mudanças Alimentares: Implicações Práticas, Teóricas e Metodológicas. In: Diez-Garcia RW, Cervato-Mancuso AM, Vannucchi H, organizadores. Mudanças alimentares e educação nutricional. Rio de Janeiro: Guanabara Koogan; 2011. p. 3-17..

Regarding the tools used for NK data collection, a wide range of tools was used; however, most authors (44%) used a questionnaire designed specifically for their study⁶6. Dickson-Spillmann M, Siegrist M. Consumers’ knowledge of healthy diets and its correlation with dietary behaviour. J Hum Nutr Diet 2011; 24(1):54-60.^,2323. Nuss H, Freeland-graves J, Clarke K, Klohe-lehman D, Milani TJ. Greater Nutrition Knowledge Is Associated with Lower 1-Year Postpartum Weight Retention in Low-Income Women. J Am Diet Assoc 2007; 107(10):1801-1806.^,2525. Pon LW, Noor-Aini MY, Ong FB, Adeeb N, Seri SS, Shamsuddin K, Mohamed AL, Hapizah N, Mokhtar A, Wan HW. Diet, nutritional knowledge and health status of urban middle-aged Malaysian women. Asia Pac J Clin Nutr 2006; 15(3):388-399.^,2828. Lin W, Lee YW. Nutrition knowledge, attitudes and dietary restriction behaviour of Taiwanese elderly. Asia Pac J Clin Nutr 2005; 14(3):221-229.^,3131. Lin W, Hang C-M, Yang H-C, Hung M-H. 2005-2008 Nutrition and Health Survey in Taiwan: the nutrition knowledge, attitude and behavior of 19-64 year old adults. Asia Pac J Clin Nutr 2011; 20(2):309-318.^,3333. Holdsworth M, Delpeuch F, Landais E, Eymard-duvernay S, Maire B. knowledge of dietary and behaviour-related determinants of non-communicable disease in urban Senegalese women. Public Health Nutr 2006; 9(8):975-981.^,3535. Zawila LG, Steib C-SM, Hoogenboom B. The Female Collegiate Cross-Country Runner: Nutritional Knowledge and Attitudes. J Athl Train 2003; 38(1):67-74.^,3939. Al Riyami A, Al Hadabi S, Abd El Aty MA, Al Kharusi H, Morsi M, Jaju S. Nutrition knowledge, beliefs and dietary habits among elderly people in Nizwa, Oman: implications for policy. East Mediterr Health J 2010; 16(8):859-867.^,4141. Galindo Gómez C, Juárez Martínez L, Shamah Levy T, García Guerra A, Avila Curiel A, Quiroz Aguilar MA. Nutritional knowledge and its association with overweight and obesity in Mexican women with low socioeconomic level. Arch Latinoam Nutr 2011; 61(4):396-405.^,4343. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240.. Researchers design their own questionnaires to include items relevant to their specific study by considering the characteristics of the population being studied¹²12. Axelson ML, Brinberg D. The measurement and conceptualization of nutrition knowledge. J Nutr Educ Behav 1992; 24(5):239-246.^,5757. Parmenter K, Wardle J. Evaluation and design of nutritional knowledge measures. J Nutr Educ Behav 2000; 32(5):269-277.. However, if there is already a data collection tool that is appropriate for a particular population, then there is no need to develop another tool (to be applied to another population), provided that the psychometric properties have been reassessed and are considered reliable⁵⁷57. Parmenter K, Wardle J. Evaluation and design of nutritional knowledge measures. J Nutr Educ Behav 2000; 32(5):269-277.. Nevertheless, even when different NK assessment questionnaires are used, the content of these questionnaires does not diverge much, and all of them provide a general view of the participants’ NK.

Of all the studies that included the cut-off used for NK classification (Chart 2), only those using the NK scale of Harnack et al.⁴⁶46. Harnack L, Block G, Subar A, Lane S, Brand R. Association of cancer prevention-related nutrition knowledge, beliefs, and attitudes to cancer prevention dietary behavior. J Am Diet Assoc 1997; 97(9):957-965., translated into and validated for Portuguese by Scagliusi et al.¹³13. Scagliusi FB, Polacow VO, Cordás TA, Coelho D, Alvarenga M, Philippi ST, Lancha Júnior AH. Tradução, adaptação e avaliação psicométrica da Escala de Conhecimento Nutricional do National Health Interview Survey Cancer Epidemiology. Rev Nutr 2006; 19(4):425-436., have used the same cut-off for NK assessment²¹21. Oliveira FL, Russo FM, Menegatti I, Toya MM, Stulbach E, Garcia LS, Peron AN, Dattilo M. Avaliação do conhecimento nutricional de atletas de judô. Lécturas Educación Física y Deportes [periódico na Internet]. 2009 [acessado 2015 Mar 06]; 14(138). Disponível em: http://www.efdeportes.com/efd138/conhecimento-nutricional-de-atletas-de-judo.htm
http://www.efdeportes.com/efd138/conheci... ^,2626. Freitas ECB, Alvarenga MS, Scagliusi FB. Avaliação do conhecimento nutricional e frequência de ingestão de grupos alimentares em vegetarianos e não vegetarianos. Rev Bras Nutr Clin 2006; 21(4):267-272.^,2727. Dattilo M, Furlanetto P, Kuroda AP, Nicastro H, Coimbra PCFC, Simony RF. Conhecimento nutricional e sua associação com o índice de massa corporal. Nutrire Rev Soc Bras Aliment Nutr 2009; 34(1):75-84.^,3030. Castro NMG, Dáttilo M, Lopes LC. Avaliação do conhecimento nutricional de mulheres fisicamente ativas e sua associação com o estado nutricional. Rev Bras Ciênc Esporte 2010; 32(1):161-172.,which indicates that the dynamics of NK are not well understood.

Regarding the associations between the analysed variables, NK was shown to be associated with age, income, and educational level²³23. Nuss H, Freeland-graves J, Clarke K, Klohe-lehman D, Milani TJ. Greater Nutrition Knowledge Is Associated with Lower 1-Year Postpartum Weight Retention in Low-Income Women. J Am Diet Assoc 2007; 107(10):1801-1806.^,2424. Parmenter K, Waller J, Wardle J. Demographic variation in nutrition knowledge in England. Health Educ Res 2000; 15(2):163-174.^,2828. Lin W, Lee YW. Nutrition knowledge, attitudes and dietary restriction behaviour of Taiwanese elderly. Asia Pac J Clin Nutr 2005; 14(3):221-229.^,3131. Lin W, Hang C-M, Yang H-C, Hung M-H. 2005-2008 Nutrition and Health Survey in Taiwan: the nutrition knowledge, attitude and behavior of 19-64 year old adults. Asia Pac J Clin Nutr 2011; 20(2):309-318.^,3232. Schaller C, James EL. The nutritional knowledge of Australian nurses. Nurse Educ Today 2005; 25(5):405-412.^,3737. Carrillo E, Varela P, Fiszman S. Influence of nutritional knowledge on the use and interpretation of Spanish nutritional food labels. J Food Sci 2012; 77(1):1-8.^,3838. Hendrie GA, Coveney J, Cox D. Exploring nutrition knowledge and the demographic variation in knowledge levels in an Australian community sample. Public Health Nutr 2008; 11(12):1365-1371.^,4040. De Vriendt T, Matthys C, Verbeke W, Pynaert I, De Henauw S. Determinants of nutrition knowledge in young and middle-aged Belgian women and the association with their dietary behaviour. Appetite 2009; 52(3):788-792.^,4242. McLeod ER, Campbell KJ, Hesketh KD. Nutrition Knowledge: A Mediator between Socioeconomic Position and Diet Quality in Australian First-Time Mothers. J Am Diet Assoc 2011; 111(5):696-704.^,4343. Mirmiran P, Mohammadi-Nasrabadi F, Omidvar N, Hosseini-Esfahani F, Hamayeli-Mehrabani H, Mehrabi Y, Azizi F. Nutritional knowledge, attitude and practice of Tehranian adults and their relation to serum lipid and lipoproteins: Tehran lipid and glucose study. Ann Nutr Metab 2010; 56(3):233-240.. Nicastro et al.⁵⁸58. Nicastro H, Dattilo M, Santos TR, Padilha HVG, Zimberg IZ, Crispim CA, Stulbach TE. Aplicação da escala de conhecimento nutricional em atletas profissionais e amadores de atletismo. Rev Bras Med Esporte 2008; 14(3):205-208., Obayashi et al.⁵⁹59. Obayashi S, Bianchi LJ, Song WO. Reliability and validity of nutrition knowledge, social-psychological factors, and food label use scales from the 1995 Diet and Health Knowledge Survey. J Nutr Educ Behav 2003; 35(2):83-91., and Sapp and Jensen⁶⁰60. Sapp SG, Jensen HH. Reliability and Validity of Nutrition Knowledge and Diet-Health Awareness Tests Developed from the 1989-1991 Diet and Health Knowledge Surveys. J Nutr Educ Behav 1997; 29(2):63-72. also showed a positive association between educational level and the NK questionnaire score, which clearly shows that education is a basic tool for obtaining knowledge on nutrition. According to Zawila et al.³⁵35. Zawila LG, Steib C-SM, Hoogenboom B. The Female Collegiate Cross-Country Runner: Nutritional Knowledge and Attitudes. J Athl Train 2003; 38(1):67-74., the greater NK observed in females supports the hypothesis that women are more concerned with aesthetic aspects, which leads them to search more for food-related information.

The studies that investigated a possible association with anthropometric data (Chart 2) show different results regarding BMI, and do not suggest a protector effect against increased body mass. Even when the evidence shows that NK may influence food choices, promote the adoption of healthy food habits, and, consequently, prevent an increase in body mass¹³13. Scagliusi FB, Polacow VO, Cordás TA, Coelho D, Alvarenga M, Philippi ST, Lancha Júnior AH. Tradução, adaptação e avaliação psicométrica da Escala de Conhecimento Nutricional do National Health Interview Survey Cancer Epidemiology. Rev Nutr 2006; 19(4):425-436.^,3030. Castro NMG, Dáttilo M, Lopes LC. Avaliação do conhecimento nutricional de mulheres fisicamente ativas e sua associação com o estado nutricional. Rev Bras Ciênc Esporte 2010; 32(1):161-172., this association is not universal. It is not clear whether NK leads to healthy food habits¹³13. Scagliusi FB, Polacow VO, Cordás TA, Coelho D, Alvarenga M, Philippi ST, Lancha Júnior AH. Tradução, adaptação e avaliação psicométrica da Escala de Conhecimento Nutricional do National Health Interview Survey Cancer Epidemiology. Rev Nutr 2006; 19(4):425-436.. According to Dattilo et al.²⁷27. Dattilo M, Furlanetto P, Kuroda AP, Nicastro H, Coimbra PCFC, Simony RF. Conhecimento nutricional e sua associação com o índice de massa corporal. Nutrire Rev Soc Bras Aliment Nutr 2009; 34(1):75-84., the available literature on NK and the nutritional status of a population is very limited, and few studies have used dully validated methods.

Regarding dietary aspects, greater NK was generally associated with healthy food choices and habits. However, even if NK might be a factor that improves eating behaviour, it is not the only determinant factor. For example, according to Montero Bravo et al.⁶¹61. Montero Bravo A, Ubeda Martín N, García González A. Evaluation of dietary habits of a population of university students in relation with their nutritional knowledge. Nutr Hosp 2006; 21(4):466-473., a study performed on 105 college students studying health-related subjects (including nutrition) revealed that, even when students thought they had good NK, the NK was not compatible with their food habits. This study demonstrates the complex nature of this research area and explains why conclusions from similar studies are in apparent disagreement; finally, it shows that further studies are necessary to assess the relationship between NK and eating behaviour, particularly due to the limitations observed in some of the articles reviewed in this study.

Conclusion

Studies assessing the level of nutrition knowledge in adults remain rare and use different assessment tools and scores, in addition to different variables, objectives, and sample sizes, hampering the analysis of its determinant factors. There is a greater tendency to assess the relationship between NK and sociodemographic and economic variables than to assess the relationship between NK and anthropometric and dietary data, including food habits and choices. Most studies here reviewed present a methodological quality classified as B according to the STROBE criteria, and only few are classified as A, which is compatible with the observed profile.

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