Abstract

Introduction

Data on food intake (FI) assessed with Food Frequency Questionnaires (FFQ) are usually collected at a particular time. Information bias could occur if the reference period for the information about FI includes the 12 previous months. As an example, if the FFQ is applied during summer, interviewees could involuntarily overestimate the foods typically consumed at this time of the year, to the detriment of foods consumed during winter. On the other hand, if the FFQ include a shorter period of time, such as three months, the information could be affected by the actual variation in the seasonal FI. This fact has been well documented and it has received significant attention in the literature¹1. Capita R, Alonso-Calleja C. Differences in reported winter and summer dietary intakes in young adults in Spain.Int J Food Sci Nutr2005; 56(6): 431-43. ^{, 2}2. Ma Y, Olendzki BC, Li W, Hafner AR, Chiriboga D, Hebert JR et al. Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population.Eur J Clin Nutr2006; 60(4): 519-28.. Similarly, this could occur when other FI assessment instruments are applied, such as the dietary record or 24-hour dietary recall (24hR). The latter can be more or less affected by the seasons, depending on the number of assessments throughout the year.

There are controversies about the seasonal effect on FI. Some studies suggest that, as an example, the daily energy intake (EI) varies significantly according to the season of the year¹1. Capita R, Alonso-Calleja C. Differences in reported winter and summer dietary intakes in young adults in Spain.Int J Food Sci Nutr2005; 56(6): 431-43. ^{, 2}2. Ma Y, Olendzki BC, Li W, Hafner AR, Chiriboga D, Hebert JR et al. Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population.Eur J Clin Nutr2006; 60(4): 519-28.. Others did not find such variation in EI³3. Subar AF, Frey CM, Harlan LC, Kahle L. Differences in reported food frequency by season of questionnaire administration: The 1987 National Health Interview Survey.Source Epidemiol1994; 5(2): 226-33. ^{, 4}4. Shahar DR, Froom P, Harari G, Yerushalmi N, Lubin F. Changes in dietary intake account for seasonal changes in cardiovascular disease rizk factors.Eur J Clin Nutr1999; 53: 395-400., but identified differences in the eating pattern between seasons⁵. However, the majority of seasonal differences in the FI is found in regions where seasons are well defined, thus influencing the availability of certain foods throughout the year¹1. Capita R, Alonso-Calleja C. Differences in reported winter and summer dietary intakes in young adults in Spain.Int J Food Sci Nutr2005; 56(6): 431-43. ^{, 6}6. Fowke JH, Schlundt D, Gong Y, Jin F, Shu X, Wen W et al., Impact of Season of Food Frequency Questionnaire Administration on Dietary Reporting.Ann Epidemiol2004; 14: 778-85. ^{, 7}7. Westerterp KR, Plasqui G, Goris AHC. Water loss as a function of energy intake, physical activity and season.Br J Nutr2005; 93: 199-203..

Considering the previously mentioned aspects, the present study aimed to assess the seasonal effect on the energy and macro- and micronutrient intakes of a sample of adults of the city of Niterói, RJ, Southeastern Brazil, where the climate is tropical.

Methods

The present study used a prospective cohort originated from the research project entitled “Construction and Validation of an Instrument to Assess the Food Intake of a Population”*, aimed at constructing and validating a FFQ⁸8. Anjos LA, Wahrlich V, Vasconcellos MTL, Souza DR, Olinto MTA, Waissmann W et al., Development of a food frequency questionnaire in a probabilistic sample of adults from Niterói, Rio de Janeiro, Brazil.Cad Saúde Pública2010; 26(11): 2196-204.. The sample comprised of 150 adult individuals who lived in the city of Niterói, RJ, Brazil. Individuals were contacted by telephone, according to a list of participants of a household survey conducted in a probabilistic sample of adults living in the city of Niterói⁹9. Souza DR, Anjos LA, Wahrlich V, Vasconcellos MTL, Machado JM. Ingestão alimentar e balanço energético da população adulta de Niterói, Rio de Janeiro, Brasil: resultados da Pesquisa de Nutrição, Atividade Física e Saúde (PNAFS).Cad Saude Publica 2010; 26(5): 879-90., based on the following criteria: being aged between 20 and 69 years; having completed at least ten years of school in the three lowest income strata or four years in the remaining income strata; not being obese or underweight, a criterion assessed with a body mass index (BMI) higher than or equal to 30 kg.m^-2and lower than 18.5 kg.m^-2, respectively; reporting not having or not being undergoing treatment for diabetes mellitus, kidney diseases, cardiovascular diseases (CVD), gastrointestinal diseases, thyroid disorders or any other diseases that could interfere with the eating pattern; not being pregnant or breast-feeding; and not being on a diet.

Individuals who agreed to participate in the study were invited to be present at the LANUFF (Nutritional and Functional Assessment Laboratory of the Fluminense Federal University) on a particular morning while fasting. They were given detailed explanations about their participation and subsequently signed an informed consent form. Socio-demographic data were obtained with a standard questionnaire, aiming to categorize socioeconomic classes¹⁰10. Associação Brasileira de Empresas de Pesquisa (ABEP).Critério de Classificação Econômica Brasil. Disponível em http://www.abep.org/codigosguias/ABEP_CCEB.pdf. (Acessado em 07 de outubro de 2008).
http://www.abep.org/codigosguias/ABEP_CC... . Body mass and stature measurements were obtained while individuals were wearing standard clothes, following the methods described by Lohman et al . ¹¹. With these measurements, BMI was calculated and participants' nutritional status was classified as either normal (18.5 ≤ BMI < 25 kg.m^-2) or overweight (25 ≤ BMI < 30 kg.m^-2)¹²12. World Health Organization.Obesity: preventing and managing the global epidemic. Geneva: World Health Organization; 2000. (WHO Technical Report Series, 824).

After these measurements were obtained, a 24hR was performed with the use of a photo album especially designed for this research project, which was provided for individuals to take home. On this occasion, three non-consecutive days were set up through telephone calls to perform this 24hR (two weekdays and one weekend day). Six months after the first dietary recall was performed, individuals were contacted again and the procedures used to obtain three more 24hR were repeated. Data collection was performed between the summer of 2007 and 2008 (January through April) and winter of 2007 (July through October).

The nutrient content of these dietary recalls were primarily obtained from the Brazilian Food Composition Table (TACO)¹³13. Universidade Estadual de Campinas.Tabela Brasileira de Composição de Alimentos, Versão II. 2. ed. Campinas: Unicamp; 2006.. Foods that were not present in the TACO were obtained from other sources⁸8. Anjos LA, Wahrlich V, Vasconcellos MTL, Souza DR, Olinto MTA, Waissmann W et al., Development of a food frequency questionnaire in a probabilistic sample of adults from Niterói, Rio de Janeiro, Brazil.Cad Saúde Pública2010; 26(11): 2196-204.: the USDA National Nutrient Database for Standard Reference – Release 20¹⁴14. United States Department of Agriculture (USDA), Agricultural Research Service.USDA National Nutrient Database for Standard Reference, Release 20; 2007.; Eating Pattern Assessment Table in Cooking Measures¹⁵15. Benzecry EH, Pinheiro ABV, Lacerda EMA, Gomes MCS, da Costa VM.Tabela para Avaliação de Consumo Alimentar em Medidas Caseiras. 5aed. São Paulo: Editora Atheneu; 2005.; and, lastly, in very specific cases (such as nutritional supplements and fast-food restaurant preparations), the nutrition facts from food labels.

Within- and between-person variances were estimated according to the three 24hRs per season, as were the individual energy and macro- and micronutrient intakes deattenuated for within-person variability (WV) using the PC-SIDE software¹⁶16. Iowa State University.Software for intake distribution estimation version 1.0. Iowa City, IA, USA; 2003.. The PC-SIDE software predicts the transformation of dietary variables to enable the symmetry of distribution before the within- and between-person variances are calculated and provides individual deattenuated values for WV in the original scale¹⁷17. Nusser SM, Carriquiry AL, Dodd KW, Fuller WA. A semi parametric transformation approach to estimating usual intake distributions.J Am Stat Assoc1996; 91: 1440-9. ^{, 18}18. Nusser SM, Fuller WA, Guenther PM. Estimating usual dietary intake distributions: adjusting for measurement error and no normality in 24-hour food intake data. In: Lyberg L, Biemer P, Collins M, De Leeuw E, Dippo C, Schwarz N, Trewin D.Survey Measurement and Process Quality. New York: Wiley and Sons; 1997. p. 689-709..

Prior to deattenuation, the three summer 24hRs were compared to each other (non-normal distribution) and as there were no significant differences among them (Kruskal-Wallis H-test with p > 0.05), they were included in the same season of the year (summer). This procedure was also performed for the three winter 24hRs.

The WV deattenuated values were used to calculate the percentage of individuals who met the recommendations (% IAR) of FI. Energy recommendations were estimated by multiplying the basal metabolic rate (BMR) – calculated by the equations suggested by the Food and Agriculture Organization (FAO)¹⁹19. Food and Agriculture Organization.Human energy requirements. Report of a joint FAO/WHO/UNU expert consultation.Rome; 2004. (FAO Food and Nutrition Technical Report Series, 1).– according to the physical activity level of 1.4, as recommended for this population²⁰20. Anjos LA, Ferreira BCM, Vasconcellos MTL, Wahrlich V. Gasto energético em adultos do Município de Niterói, Rio de Janeiro: Resultados da Pesquisa de Nutrição, Atividade Física e Saúde – PNAFS.Cien Saude Colet2008; 13(6): 1775-84.. The acceptable macronutrient distribution range of the Dietary Reference Intakes (DRI)²¹21. Institute of Medicine.Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients).Washington, DC, National Academic Press; 2005.was used as recommendations for protein, carbohydrate and total fat intakes. The recommendations from the Brazilian Cardiology Society²²22. Sociedade Brasileira de Cardiologia (SBC), Departamento de aterosclerose.V Diretriz brasileira sobre dislipidemias e prevenção da aterosclerose; 2008.for saturated, mono- and polyunsaturated fats were used for these dietary components. The recommendations for fibers, calcium, manganese, sodium and potassium were based on adequate intake values, according to the DRI. The recommended dietary intake values for magnesium, phosphorus, iron, copper, zinc, retinol, thiamin, riboflavin, pyridoxine, niacin and vitamin C were used²¹21. Institute of Medicine.Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients).Washington, DC, National Academic Press; 2005. ^{, 23}23. Institute of Medicine.Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride.Washington, DC, National Academic Press; 1997.

24. Institute of Medicine.Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic acid, Biotin and Coline. Washington, DC, National Academic Press; 1998.

25. Institute of Medicine.Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC, National Academic Press; 2000a.

26. Institute of Medicine.Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc.Washington, DC, National Academic Press; 2000b. ^{- 27}27. Institute of Medicine.Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC, National Academic Press; 2004..

The intake of macro- and micronutrients, deattenuated for WV, was adjusted for EI, using the residue method²⁹29. SAS Institute Inc. SAS 9.1. Cary, NC, USA; 2002/2003.. The objective of the adjustment for EI was to remove possible confounding factors that could occur with the total EI and this is a requirement for studies on nutrient intake assessment²⁸28. Willett WC, Howe GR, Kushi LH. Adjustment for total energy intake in epidemiologic studies.Am J Clin Nutr1997; 65(S1): 1220-8..

The adjustment for EI did not lead to satisfactory results for the intake of retinol in women and men and that of copper and riboflavin in men. For this reason, these data were not shown.

The means (and standard deviations – SD) of the most adequate unit of measurement and the % IAR were estimated for the energy and macro- and micronutrient intakes in the summer and winter for both sexes. The mean intakes, deattenuated for WV only and deattenuated and adjusted for EI, were compared between sexes and seasons of the year. The difference between means was tested using the non-parametric test (Wilcoxon), as variables did not show a normal distribution. In all statistical tests, the value of α = 0.05 was used to determine the significance.

The data analysis was performed with the Statistical Analysis System (SAS) version 9.1, Software for Intake Distribution Estimation (PC-SIDE) version 1.0 and Statistical Package for the Social Sciences (SPSS) version 13.0¹⁶16. Iowa State University.Software for intake distribution estimation version 1.0. Iowa City, IA, USA; 2003. ^{, 29}29. SAS Institute Inc. SAS 9.1. Cary, NC, USA; 2002/2003. ^{, 30}30. SPSS Inc. SPSS 13.0 for Windows. Chicago, IL, USA; 2004..

The research project was approved by the Research Ethics Committee of the Medical School of the Fluminense Federal University under number 163/06. There were no conflicts of interest during the development of the study.

Results

A total of 102 individuals (69 women) completed the present study. Approximately 54% of the sample belonged to socioeconomic class B, the majority was aged between 40 and 49 years (25.5%) and had normal BMI (63.7%), and the prevalence of overweight was higher in men (51.5%) than women (29.0%) ( Table 1 ).

The majority of losses was due to individuals' refusal to participate in the second stage of the study and those who were lost to follow-up had similar characteristics to the ones who remained in the analysis: the majority were women (56.3%) and aged between 40 and 49 years (31.3%), belonged to socioeconomic class B (45.5%), and had a higher prevalence of overweight compared to men.

The intake of energy and of certain nutrients (protein, fat, carbohydrate and pyridoxine) was significantly different between men and women for the WV-deattenuated EI-adjusted values. In general, EI and nutrient intake were higher in men than in women. There were no differences between seasons of the year for the mean WV-deattenuated EI both in women and men (Tables 2 and 3).

Protein intake among men was higher during summer than winter ( Table 2 ). Among women, the highest intake occurred during winter, although only for proteins adjusted for EI ( Table 3 ). There were no differences in fat intake of men between seasons of the year; however, this intake adjusted for EI was different between summer and winter among women. EI-adjusted carbohydrate intake was greater during winter, compared to summer in men ( Table 2 ), whereas the intake of carbohydrates by women was not different between seasons of the year, both for WV-deattenuated values and those adjusted for EI ( Table 3 ).

Cholesterol intake was different between seasons of the year in men only and this intake was higher during summer ( Table 2 ), whereas the intake of saturated fats adjusted for EI was only different among women and it was higher during winter ( Table 3 ). With regard to monounsaturated fats, again there were only differences in intake among women, which was higher during winter ( Table 3 ). There were no differences in the intake of polyunsaturated fats in men between seasons ( Table 2 ). In contrast, among women, this difference occurred in both types of adjustment ( Table 3 ).

In general, both men and women had higher fiber intake adjusted for EI during winter, when compared to the summer. Concerning the differences in intake of minerals and vitamins between seasons, there was a higher intake of calcium, magnesium, phosphorus, copper, potassium, thiamin and pyridoxine during winter by women (Table 2 and 3).

The majority of women and men did not meet the recommendations of calcium, magnesium, potassium, retinol and polyunsaturated fats. In addition to these nutrients, a higher percentage of men did not meet the recommendations for protein (winter), pyridoxine (winter), monounsaturated fats (winter), thiamin (summer), fibers and vitamin C (both seasons) ( Figure 1a ). Among women, the corresponding nutrients were fibers (summer), monounsaturated fats (summer), iron and pyridoxine (both seasons) ( Figure 1b ).

Discussion

Several studies assessed possible sources of variability capable of interfering with the measurement of FI of populations, such as seasonality¹1. Capita R, Alonso-Calleja C. Differences in reported winter and summer dietary intakes in young adults in Spain.Int J Food Sci Nutr2005; 56(6): 431-43.

2. Ma Y, Olendzki BC, Li W, Hafner AR, Chiriboga D, Hebert JR et al. Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population.Eur J Clin Nutr2006; 60(4): 519-28.

3. Subar AF, Frey CM, Harlan LC, Kahle L. Differences in reported food frequency by season of questionnaire administration: The 1987 National Health Interview Survey.Source Epidemiol1994; 5(2): 226-33.

4. Shahar DR, Froom P, Harari G, Yerushalmi N, Lubin F. Changes in dietary intake account for seasonal changes in cardiovascular disease rizk factors.Eur J Clin Nutr1999; 53: 395-400.

5. Mitchikpe CES, Dossa RAM, Ategbo EAD, Van Raaij JMA, Kok Fj. Seasonal variation in food patern but not in energy and nutrient intakes of rural Beninese school-aged children.Public Health Nutr2009; 12(3): 414-22.

6. Fowke JH, Schlundt D, Gong Y, Jin F, Shu X, Wen W et al., Impact of Season of Food Frequency Questionnaire Administration on Dietary Reporting.Ann Epidemiol2004; 14: 778-85. ^{- 7}7. Westerterp KR, Plasqui G, Goris AHC. Water loss as a function of energy intake, physical activity and season.Br J Nutr2005; 93: 199-203.. The effect of seasonality on FI depends on cultural, ecological, geographic and meteorological factors and the industrialization level of a country³¹31. Willett WC.Nutritional Epidemiology. 2. ed. New York: Oxford University Press; 1998., apart from factors intrinsic to individuals (sex and age).

In the present study, the assessment of the energy and macro- and micronutrient intakes was obtained in two seasons of the year: summer and winter, using more than one statistical adjustment. The data shown here were corrected for WV, thus enabling the intake distribution to be exclusively influenced by the differences among indivi­duals. Fluctuations in individual daily intake can change the results and its adjustment allows the reduction in estimates of variability such as standard deviation and error³²32. Hoffman K, Boeing H, Dufour A, Volatier JL, Telman J, Virtanen M et al., Estimating the distribution of usual dietary intake by short-term measurements.Eur J Clin Nutr2002; 56(S2): 53-62. ^{, 33}33. Carriquiry A. Estimation of Usual Intake Distributions of Nutrients and Foods. J Nutr 2003; 133(S): 601-8.. Furthermore, these results were adjusted for EI, enabling the intake of women and men to be compared in both seasons of the year, without being influenced by the supply of energy³¹31. Willett WC.Nutritional Epidemiology. 2. ed. New York: Oxford University Press; 1998..

The EI was not different between seasons for the WV-deattenuated results for both sexes, showing that the EI remains the same in the sample of adults of the city of Niterói throughout the year. Consequently, the intake of different types of food will not change the EI in general, but that of certain micronutrients will, confirming that the quality of foods characterizing the dietary pattern of individuals is different throughout the year. This corroborates other studies that have used 24hRs²2. Ma Y, Olendzki BC, Li W, Hafner AR, Chiriboga D, Hebert JR et al. Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population.Eur J Clin Nutr2006; 60(4): 519-28.,³⁴34. Van Staveren WA, Deurenberg P, Burema J, De Groot LC, Hautvast JG. Seasonal variation in food intake, pattern of physical activity and change in body weight in a group of young adult Dutch women consuming self-selected diets. Int J Obes 1986; 10(2): 133-45.and FFQs²2. Ma Y, Olendzki BC, Li W, Hafner AR, Chiriboga D, Hebert JR et al. Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population.Eur J Clin Nutr2006; 60(4): 519-28. ^{, 35}35. Shahar DR, Yerushalmi N, Lubin F, Froom P, Shahar A, Kristal-Boneh E. Seasonal variations in dietary intake affect the consistency of dietary assessment.Eur J Clin Nutr2001; 17: 129-33..

In Brazil, studies that assess the seasonal variations in FI are rare. In general, the sources of variation in the FI of Brazilians studied are limited to methodological variations intrinsic to individuals. There were two studies³⁶36. Pasqua, IC.Comportamento alimentar e estado nutricional de trabalhadores em turnos: uma abordagem cronobiológica[dissertação de mestrado]. São Paulo: Universidade de São Paulo, Faculdade de Saúde Pública; 2003. ^{, 37}37. Rossato SL, Olinto MTA, Henn R, Anjos LA, Bressan A, Wahrlich V. Seasonal Effect on Nutrient Intake in Adults Living in Southern Brasil.Cad Saude Publica2010; 26(11): 2177-87.that showed results associating seasonality and FI in Brazil. In the first one, a variation was found in the eating behavior of workers with fixed shifts in the city of São Paulo between summer and winter by applying dietary recalls for three days. The diet of workers had a higher amount of energy, carbohydrates and fats during winter, showing the influence of seasonality on the FI of the sample of men.

Rossato et al.³⁷37. Rossato SL, Olinto MTA, Henn R, Anjos LA, Bressan A, Wahrlich V. Seasonal Effect on Nutrient Intake in Adults Living in Southern Brasil.Cad Saude Publica2010; 26(11): 2177-87.analyzed the seasonal variation in FI of healthy adults living in the state of Rio Grande do Sul, Southern Brazil, using six 24hRs throughout the year. The intake of carbohydrates adjusted for EI was higher during summer, compared to other seasons, contrary to what was observed for fats, whose intake was higher during winter. According to the present study, there were no differences in EI in both sexes between seasons, strengthening the hypothesis that what changes throughout the year is in fact the dietary pattern.

However, in international studies, different EI values were found throughout the year. When the FI of American women aged between 51and 86 years was assessed with a questionnaire of assessment of seasonal dietary patterns, Lee et al.³⁸38. Lee CJ, Lawler GS, Panemangalore M, Street D. Nutritional status of middle-aged and elderly females in Kentucky in two seasons: Part 1. Body weight and related factors.J Am Coll Nutr1897; 6(3): 209-15.found higher EI during winter than summer. Based on data from a cohort study conducted in Shanghai, China, Fowke et al.⁶6. Fowke JH, Schlundt D, Gong Y, Jin F, Shu X, Wen W et al., Impact of Season of Food Frequency Questionnaire Administration on Dietary Reporting.Ann Epidemiol2004; 14: 778-85.found higher EI during winter than summer in healthy women, using a FFQ. Likewise, Westerterp et al.⁷7. Westerterp KR, Plasqui G, Goris AHC. Water loss as a function of energy intake, physical activity and season.Br J Nutr2005; 93: 199-203. found higher EI by Dutch adults during winter than summer, as assessed with a seven-day dietary recall. Nonetheless, Kuhnlein et al.³⁹39. Kuhnlein HV, Soueida R, Receveur O. Dietary nutrient profiles of Canadian Baffin Island Inuit differ by food source, season, and age. J Am Diet Assoc 1996; 96: 155-62. did not find differences in EI originated from industrially processed foods, known as “market foods”, when compared to traditional unprocessed foods in Canadian women aged between 40 and 70 years, assessed during six moments of the year.

Important seasonal differences were found for the intake of nutrients associated with nutritional diseases (iron-deficiency anemia) and non-communicable chronic diseases (hypercholesterolemia, CVD and osteoporosis) in the present sample of adults of Niterói. The intake of iron and cholesterol by men was higher during summer, whereas that of calcium by women was higher during winter. This fact should be emphasized, as the need for the regular intake of such nutrients throughout the year is known, so as to guarantee a high level of health.

Tokudome et al.⁴⁰40. Tokudome Y, Imaeda N, Nagaya T, Ikeda M, Fujiwara N, Sato J et al., Daily, Weekly, Seasonal, Within- and Between-individual Variation in Nutrient Intake According to Four Season Consecutive 7 Day Weighed Diet Records in Japanese Female Dietitians.J Epidemiol2002; 12: 85-92. found results similar to those found in the present study, using dietary recalls with weighing during seven consecutive days, associated with the intake of potassium, calcium, magnesium, copper and saturated, mono- and polyunsaturated fats in Japanese women, which was significantly higher during winter. In Spain, Capita & Alonso-Calleja¹1. Capita R, Alonso-Calleja C. Differences in reported winter and summer dietary intakes in young adults in Spain.Int J Food Sci Nutr2005; 56(6): 431-43.also found higher intake of carbohydrate and fiber by men during winter and that of protein, fiber and polyunsaturated fats by women, using dietary records applied throughout one year.

The results of the present study showed a high percentage of adults that did not meet the recommendations for certain nutrients, including differences according to sex and seasons of the year and suggesting the need for distinct interventions in this population. The low iron intake by women was highly significant, while there was a low intake of fiber, niacin and vitamin C among men. The low iron intake of women could be associated with the occurrence of iron-deficiency anemia, a situation found in several studies conducted in samples of Brazilians⁴¹41. Lopes MCS, Ferreira LOC, Batista-Filho M. Uso diário e semanal de sulfato ferroso no tratamento de anemia em mulheres no período reprodutivo.Cad Saude Publica1999; 15(4): 799-808.

42. Nascimento SF.Estado nutricional e anemia em adolescentes do sexo feminino no Estado de Pernambuco, 1997[dissertação de mestrado]. Recife: Universidade Federal de Pernambuco, Centro de Ciências da Saúde, Departamento de Nutrição; 2000.

43. Olinto MTA, da Costa JSD, Gigante DP, Menezes AMB, Macedo S, Schwengber R et al., Prevalência de anemia em mulheres em idade reprodutiva no Sul do Brasil.Bol Saude2003; 17(1): 135-44. ^{- 44}44. Fabian C, Olinto MTA, da Costa JSD, Bairros F, Nácul L. Prevalência de anemia e fatores associados em mulheres adultas residentes em São Leopoldo, Rio Grande do Sul, Brasil.Cad Saude Publica2007; 23(5): 1199-205., emphasizing the need for interventions in this group.

A higher percentage of men did not meet the recommendations of proteins and monounsaturated fats during winter. Among women, a higher percentage did not meet the recommendations for fiber and monounsaturated fats during summer. In this sample, a high percentage of women and men did not meet the recommendations of calcium, retinol and saturated fats in both seasons of the year, which could be associated with osteoporosis⁴⁵, hypovitaminosis A⁴⁶46. Diniz AS, Santos LMP. Epidemiologia da hipovitamino A e xeroftalmia. In: Kac G, Sichieri R, Gigante D. (Eds).Epidemiologia Nutricional. Rio de Janeiro: Fiocruz/Atheneu; 2007. p. 325-46.and CVD, respectively²²22. Sociedade Brasileira de Cardiologia (SBC), Departamento de aterosclerose.V Diretriz brasileira sobre dislipidemias e prevenção da aterosclerose; 2008..

On the other hand, the intake of sodium, cholesterol and saturated fats, well above the recommendations for women and men in both seasons of the year, can increase the risk of CVD, such as arterial hypertension and atherosclerosis, both highly prevalent in the Brazilian population²²22. Sociedade Brasileira de Cardiologia (SBC), Departamento de aterosclerose.V Diretriz brasileira sobre dislipidemias e prevenção da aterosclerose; 2008. ^{, 47}47. Gimeno SGA, Ferreira SRG. Fatores da dieta nas doenças cardiovasculares. In: Kac G, Sichieri R, Gigante D. (Eds). Epidemiologia Nutricional. Rio de Janeiro: Fiocruz/Atheneu; 2007. p. 371-87.. Furthermore, the high percentage of men and women with higher than recommended EI should be emphasized. This finding is alarming, considering the high indices of overweight and obesity in the Brazilian population²⁰20. Anjos LA, Ferreira BCM, Vasconcellos MTL, Wahrlich V. Gasto energético em adultos do Município de Niterói, Rio de Janeiro: Resultados da Pesquisa de Nutrição, Atividade Física e Saúde – PNAFS.Cien Saude Colet2008; 13(6): 1775-84. ^{, 22}22. Sociedade Brasileira de Cardiologia (SBC), Departamento de aterosclerose.V Diretriz brasileira sobre dislipidemias e prevenção da aterosclerose; 2008..

There are certain limitations when determining whether the recommendations have been met in population studies. The insufficient intake of calcium and fiber could be partly explained by the high nutritional recommendations proposed. The intake of other nutrients such as retinol and polyunsaturated fats could be underestimated, due to their high concentration in few foods. A high percentage of individuals who did not meet the recommendations could also be associated with the limitations of food composition tables, where foods and their nutritional values are insufficiently described, leading to the use of several sources and information about food preparations⁴⁸48. Anjos LA, de Souza DR, Rossato SL. Desafios na medição da ingestão alimentar quantitativa de populações.Rev Nutr2009; 22(1): 151-61..

The present study had some limitations. The data were based on a convenient sample, not representative of the population studied, although sufficient to achieve the objective (validation of a FFQ) of the research project from which it originated. Additionally, there was a higher percentage of adults of the socioeconomic class A in the sample studied (17.7%), compared to the 5.1% estimated for the population of the metropolitan area of the city of Rio de Janeiro¹⁰10. Associação Brasileira de Empresas de Pesquisa (ABEP).Critério de Classificação Econômica Brasil. Disponível em http://www.abep.org/codigosguias/ABEP_CCEB.pdf. (Acessado em 07 de outubro de 2008).
http://www.abep.org/codigosguias/ABEP_CC... . On the other hand, the majority of the population of the present study had a normal BMI, based on the inclusion criteria proposed, thus reducing the chances of underreporting of FI due to overweight and obesity⁴⁸48. Anjos LA, de Souza DR, Rossato SL. Desafios na medição da ingestão alimentar quantitativa de populações.Rev Nutr2009; 22(1): 151-61.. Despite these limitations, the importance of seasonality in the measurement of FI of the population studied became clear.

To replicate the number of 24hRs used during different periods of the year and to include non-consecutive weekdays and weekend days, both of which were successfully achieved in the present study, are essential to plan dietary surveys, thus reducing possible sources of random errors. Measurement errors caused by seasonality can be equally diluted among individuals in the case of large samples; in contrast, lack of distortion cannot be guaranteed in the results of FI due to seasonality²2. Ma Y, Olendzki BC, Li W, Hafner AR, Chiriboga D, Hebert JR et al. Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population.Eur J Clin Nutr2006; 60(4): 519-28. ^{, 49}49. Joachim G. The influence of time on dietary data: differences in reported summer and winter food consumption.Nutr Health1997; 12(1): 33-43.. Additionally, although the city of Niterói does not have well defined seasons due to its tropical location, significant differences in FI were found in the present study.

In conclusion, although the majority of national and international studies have not included seasonality, the results shown here indicate that this source of variation should be taken into consideration, even in tropical regions.

Authors' contributions: LA Anjos, MTA Olinto and W Waissmann were responsible for planning the original research. AF Costa, LA Anjos and V Wahrlich supervised the field data collection. EM Yokoo and RL Henn helped with data analysis and manuscript writing. AF Costa analyzed the data, discussed the results and wrote the first version of the manuscript, which was subsequently reviewed and approved by all authors.

Acknowledgements:

AF Costa was granted a scholarship by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES – Coordination for the Improvement of Higher Education Personnel). This research project was funded by the CAPES in the National Academic Cooperation Program (PROCAD; process 0257052). LA Anjos (process 311801/2006-4 and 308489/2009-8) and MTA Olinto (process 308833/2006-6) were granted research productivity scholarships by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – National Council for Scientific and Technological Development).

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