Abstract:

The study aimed to compare biomarkers in groups of adolescents classified simultaneously according to body mass index (BMI) and body fat percentage measured by air displacement plethysmography. This was a cross-sectional study with 533 adolescents 18 to 19 years of age in São Luís, Maranhão, Brazil. BMI was classified as adequate (< 25kg/m²) versus excess weight (≥ 25kg/m²). High body fat percentage was defined as ≥ 25% for males and ≥ 30% for females. The adolescents were classified in four groups: “normal weight” (adequate BMI and body fat percentage), “normal weight obese” (adequate BMI with high body fat percentage), “excess weight with adequate body fat percentage”, and “excess weight with high body fat percentage”. Girls showed higher proportions of “normal weight obesity” (15.6%) and “excess weight with high body fat percentage” (17.1%). “Normal weight obese” adolescents exhibited higher mean values for total cholesterol (172.5mg/dL) and LDL-cholesterol (103.5mg/dL). Those with “excess weight and high body fat percentage” showed lower mean HDL-cholesterol (43.2mg/dL) compared to the other groups, higher mean interleukin-6 (2.7pg/mL) than “normal weight” and “excess weight and adequate body fat percentage” adolescents, and higher median triglycerides (114.0mg/dL) and C-reactive protein (0.14ng/mL) than “normal weight” and “normal weight obese” adolescents. Those with “excess weight and adequate body fat percentage” exhibited the same C-reactive protein levels as those with “excess weight and high body fat percentage”. Assessment of nutritional status by BMI alone is limited, since 6.8% of the adolescents presented high body fat percentage despite normal BMI, and those who were “normal weight obese” had two biomarkers that were worse than for adolescents with “excess weight and high body fat percentage”.

Keywords:
Body Mass Index; Adiposity; Biomarkers; Interleukin-6

Introduction

Body mass index (BMI) has been the most widely used indicator for assessing nutritional status and was established as the basis for classification of obesity, defined as excess adiposity. Although BMI is capable of identifying excess body weight, it fails to distinguish between fat mass and fat-free mass. BMI thus significantly underestimates obesity prevalence ¹1. Shah NR, Braverman ER. Measuring adiposity in patients: the utility of body mass index (BMI), percent body fat, and leptin. PLoS One 2012; 7:e33308..

Due to this limitation, individuals with adequate BMI may present high body fat percentage, and are thus called normal weight obese ²2. De Lorenzo A, Martinoli R, Vaia F, Di Renzo L. Normal weight obese (NWO) women: an evaluation of a candidate new syndrome. Nutr Metab Cardiovasc Dis 2006; 16:513-23.. There is a significant prevalence of individuals misclassified as healthy, simply because their BMI falls within the normal range, leaving a high percentage of false-negatives. Likewise, individuals with preserved or increased lean mass and adequate adiposity may be misclassified in the excess weight category according to BMI (although this percentage of false-positives is low) ³3. Berg CM, Strandhagen E, Mehlig K, Subramoney S, Lissner L, Björck L. Normal weight adiposity in a Swedish population: how well is cardiovascular risk associated with excess body fat captured by BMI? Obes Sci Pract 2015; 1:50-8..

Studies have reported an association between high body fat percentage and increased risk of dyslipidemias, diabetes, metabolic syndrome, and cardiovascular mortality, even in individuals with adequate BMI ³3. Berg CM, Strandhagen E, Mehlig K, Subramoney S, Lissner L, Björck L. Normal weight adiposity in a Swedish population: how well is cardiovascular risk associated with excess body fat captured by BMI? Obes Sci Pract 2015; 1:50-8.^,44. Martinez KE, Tucker LA, Bailey BW, LeCheminant JD. Expanded normal weight obesity and insulin resistance in US adults of the National Health and Nutrition Examination Survey. J Diabetes Res 2017; 2017:9502643.. Serrano et al. ⁵5. Serrano HMS, Carvalho GQ, Pereira PF, Peluzio MCG, Franceschini SCC, Priore SE. Composição corpórea, alterações bioquímicas e clínicas de adolescentes com excesso de adiposidade. Arq Bras Cardiol 2010; 95:464-72. found that female adolescents who were normal weight obese measured by bioelectrical impedance presented altered blood pressure and low-density lipoprotein cholesterol (LDL), similar to adolescents with excess weight.

Individuals with high body fat percentage may also present higher production and secretion of proinflammatory cytokines such as interleukin-6 and tumor necrosis factor alpha (TNF-α), a condition associated with the development of cardiovascular diseases, insulin resistance, and atherosclerotic processes. Thus, elevated rates of these cytokines can be considered indicators of cardiovascular risk and metabolic syndrome in obese individuals with normal weight ²2. De Lorenzo A, Martinoli R, Vaia F, Di Renzo L. Normal weight obese (NWO) women: an evaluation of a candidate new syndrome. Nutr Metab Cardiovasc Dis 2006; 16:513-23..

To ensure greater validity in nutritional diagnosis, it is necessary to use biomarkers and methods capable of valid estimation of body composition ⁵5. Serrano HMS, Carvalho GQ, Pereira PF, Peluzio MCG, Franceschini SCC, Priore SE. Composição corpórea, alterações bioquímicas e clínicas de adolescentes com excesso de adiposidade. Arq Bras Cardiol 2010; 95:464-72.. The available methods feature air displacement plethysmography (ADP), which is valid in different populations, and whose estimate of body composition does not differ from that of hydrostatic weighing, considered the gold standard ⁶6. Mello MT, Dâmaso AR, Antunes HK, Siqueira KO, Castro ML, Bertolino SV, et al. Avaliação da composição corporal em adolescentes obesos: o uso de dois diferentes métodos. Rev Bras Med Esporte 2005; 11:267-70.. The current study thus proposes to compare biomarkers in four groups of adolescents from the RPS Cohort in São Luís, Maranhão, Brazil, classified simultaneously by BMI and body fat percentage assessed by ADP.

Methods

Study design

This was a cross-sectional study whose data source was a birth cohort in São Luís, and entitled Lifetime Determinants of Obesity, Precursors of Chronic Diseases, Human Capital, and Mental Health: A Contribution from the São Luís Birth Cohorts to the Brazilian Unified National Health System - SUS. This study is part of the RPS Consortium, which includes other studies performed in the cities of Ribeirão Preto (São Paulo State) and Pelotas (Rio Grande do Sul State).

This São Luís birth cohort included live hospital births to mothers living in the municipality, from March 1997 to February 1998. Participants in this cohort were assessed in three life phases: birth, childhood (7 to 9 years), and adolescence (18 to 19 years). The current study used data from the third phase.

Participants

The birth cohort was conducted in ten public and private hospitals providing obstetric care. Systematic sampling was used with stratification proportional to the number of births in each hospital. One out of seven births were recruited in each hospital, covering 2,542 births in this phase of the cohort. The target population covered 96.3% of all births in São Luís (20,092) in the year 1996. With the exclusion of twins and stillbirths, the final sample in this first phase totaled 2,443 live births ⁷7. Cardoso VC, Simões VMF, Barbieri MA, Silva AAM, Bettiol H, Alves MTSSB, et al. Profile of three Brazilian birth cohort studies in Ribeirão Preto, SP and São Luís, MA. Braz J Med Biol Res 2007; 40:1165-76..

In the third phase of the cohort, participants were located through searches in school and university enrollment lists, at the addresses and telephone contacts recorded during the first and second phases of the cohort, on the military enlistment rosters for boys, and on social media. A total of 659 adolescents were identified and agreed to participate and appeared for the data collection. The current study considered data from 533 participants, since 106 did not have their biomarkers measured, while 20 lacked anthropometric data (Figure 1).

Data collection and study variables

The data were collected by trained health professionals. The information was recorded in the online program Research Electronic Data Capture (REDcap. https://www.project-redcap.org/) ⁸8. Harris PA, Taylor R, Thielke R, Payne J, Gonzalez N, Conde JG. Research electronic data capture (REDcap): a metadata-driven methodology and workflow process for providing translational research informatics support. J Biomed Inform 2009; 42:377-81.. The variables sex (male and female) and age (years) were collected with a questionnaire.

Anthropometric and body composition assessments were performed. Height was measured in centimeters with a stadiometer (Alturexata, Belo Horizonte, Brazil). Total body mass was obtained in kilograms with a Filizola scale (São Paulo, Brazil). BMI was calculated as weight in kilograms divided by height in meters squared, and was classified as adequate versus excess weight (overweight and obesity) according to World Health Organization (WHO) guidelines (≥ 25kg/m²) ⁹9. World Health Organization. physical status: the use and interpretation of anthropometry. Geneva: World Health Organziation; 1995.. Waist circumference (in centimeters) was obtained with the Dimensional Photonic Scanner - 3DPS ([TC] ² Labs, Cary, United States), which produces a 3D image of the body.

The adolescents had their body fat percentage assessed with ADP (Bod Pod Gold Standard, COSMED - Rome, Italy). Based on the body volume measured by ADP and body mass, the equipment calculated the body density, which was used in the Siri equation to determine the adolescents’ fat mass ¹⁰10. Siri WE. Body composition from fluid spaces and density: analysis of methods 1961. Nutrition 1993; 9:480-91.. The adolescents wore a cap to hold down their hair and light clothing to minimize the potential error from isothermal air that can be trapped in the clothing and hair. They were barefoot, with no earrings, rings, dental prostheses, or other types of metallic materials. The equipment was calibrated daily with a known volume of 50 liters. Body fat percentage was classified according to the Williams criteria ¹¹11. Williams DP, Going SB, Lohman TG, Harsha DW, Srinivasan SR, Webber LS, et al. Body fatness and risk for elevated blood pressure, total cholesterol, and serum lipoprotein ratios in children and adolescents. Am J Public Health 1992; 82:358-63 (1992) as normal (< 25% for males and < 30% for females) versus high (≥ 25% for males and ≥ 30% for females).

Muscle mass (in kilograms) was measured by dual-emission x-ray absorptiometry (DEXA) based on enCORE and the Lunar Prodigy model (GE Healthcare - Chicago, United States).

Level of physical activity was measured with the 24-Hour Physical Activity Survey, based on an adaptation of the Self-Administered Physical Activity Checklist (SAPAC) ¹²12. Sallis JF, Strikmiller PK, Harsha DW, Feldman HA, Ehlinger S, Stone EJ, et al. Validation of interviewer-and self-administered physical activity checklists for fifth grade students. Med Sci Sports Exerc 1996; 28:840-51.. Level of physical activity was calculated by the number of metabolic task equivalents (MTEs) per week, where the time spent on each activity was multiplied by the activity’s MTE and the number of days the adolescent practiced that activity. MTEs for each activity were obtained from the Compendium of Physical Activities (CPA) ¹³13. Ainsworth BE, Haskell WL, Leon AS, Jacobs DR, Montoye HJ, Sallis JF, et al. Compendium of physical activities: classification of energy costs of human physical activities. Med Sci Sports Exerc 1993; 25:71-80.. Classification of level of physical activity used the cutoff points from the International Physical Activity Questionnaire (IPAQ) in MTEs/week: sedentary (0), low (1 to < 600), moderate (600 to < 3,000), and high (≥ 3,000) ¹⁴14. Benedetti TRB, Antunes PC, Rodriguez-Añez CR, Mazo GZ, Petroski EL. Reprodutibilidade e validade do Questionário Internacional de Atividade Física (IPAQ) em homens idosos. Rev Bras Med Esporte 2007; 13:11-6..

Blood samples (40 ml) were drawn aseptically from the cubital vein by a technician with experience in this procedure. The samples were stored in a freezer at adequate temperatures for each type of analysis (-20 or -80ºC) until tested. The blood analysis measured interferon gamma (IFN-γ) in pg/mL, interleukin-4 (IL-4) in pg/mL, interleukin-17 (IL-17) in pg/mL, vascular endothelial growth factor (VEGF) in pg/mL, C-reactive protein (CRP) in ng/mL, interleukin-6 (IL-6) in pg/mL, hepatocyte growth factor (HGF) in pg/mL, tumor necrosis factor alpha (TNF-α) in pg/mL, and regulated on activation, normal T-cell expressed and secreted (RANTES) in pg/mL. These biomarkers were analyzed with Milliplex MAP Human Cytokine Kit (Merck, Darmstadt, Germany) (Table 1).

A four-group classification was defined, using BMI and body fat percentage simultaneously: “normal weight” (adequate BMI and body fat percentage), “normal weight obese” (adequate BMI with high body fat percentage), “excess weight with adequate body fat percentage”, and “excess weight with high body fat percentage”.

Statistical analysis

Data were analyzed with the Stata software, version 14.0 (https://www.stata.com). Categorical variables were described by absolute and relative frequencies. Chi-square test was performed to verify whether there was a difference between the groups’ frequencies, gender, and level of physical activity. Normal distribution of the continuous variables was verified with the Shapiro-Wilk test and asymmetry and kurtosis coefficients. Continuous variables with normal distribution were presented by the mean and standard deviation and analyzed by the ANOVA test, and those without normal distribution were described by the median and interquartile range and analyzed by the Kruskal-Wallis test to verify differences in the measure of central tendency between the groups. We opted not to perform the analysis between groups and the biomarkers separated by sex, since there were only four boys with “normal weight obesity” and four girls with “excess weight and high body fat percentage”.

Ethical and legal aspects

The study was approved by the Institutional Review Board of the University Hospital, Federal University of Maranhão, protocol number 1.302.489. All participants signed a free and informed consent form.

Results

The study assessed 533 adolescents, 18 to 19 years of age, of whom 61.5% were boys. Boys showed a higher proportion of “excess weight and adequate body fat percentage” (8.3%) compared to girls, who had higher proportions of “normal weight obesity” (15.6%) and “excess weight with high body fat percentage” (17.1%) (Table 2).

Higher mean waist circumference was seen in adolescents with “excess weight and high body fat percentage” (96cm) compared to “normal weight” and “normal weight obese” individuals, besides higher mean body fat percentage in adolescents with “excess weight and high body fat percentage” (35.1%) and “normal weight obesity” (34.2%) compared to “normal weight” (14.4%) and “excess weight and adequate body fat percentage” (18.8%) individuals. Adolescents with “excess weight and adequate body fat percentage” exhibited higher mean muscle mass (54.5kg) and higher rates of high physical activity (32.2%) and moderate physical activity (35.5%). “Normal weight obese” adolescents were more sedentary (66.7%) (Table 3).

In relation to biomarkers, “normal weight obese” adolescents presented the highest mean total cholesterol (172.5mg/dL) and LDL-cholesterol (103.5mg/dL) among all the groups. Those with “excess weight and high body fat percentage” exhibited lower mean high-density lipoprotein cholesterol (HDL-cholesterol - 43.2mg/dL) than the other groups; higher mean IL-6 (2.7pg/mL) than the “normal weight” and “excess weight and adequate body fat percentage” adolescents; and higher median triglycerides (114.0mg/dL) and CRP (0.14ng/mL) compared to their “normal weight” and “normal weight obese” peers. Adolescents with “excess weight and adequate body fat percentage” presented CRP equal to those with “excess weight and high body fat percentage” (0.14ng/mL), but higher than the “normal weight” adolescents (0.06ng/mL) (Table 4).

Discussion

Adolescents in this study with “excess weight and high body fat percentage” presented four biomarkers with worse values (triglycerides, HDL-cholesterol, IL-6, and CRP), “normal weight obese” had two higher biomarkers (total cholesterol and LDL-cholesterol), and those with “excess weight and adequate body fat percentage” had one elevated biomarker (CRP) compared to their “normal weight” peers. The main result is that adolescents with “excess weight and high body fat percentage” had a worse lipid and inflammatory profile. Some adolescents also showed high body fat percentage despite normal BMI, or so-called “normal weight obese” individuals, with higher values for some lipid markers. Thus, the use of BMI alone has limited capacity to assess obesity and the risk of atherosclerotic and cardiovascular diseases in adolescents.

The study presents some limitations. Loss to follow-up of participants in the cohort was 20.9%. Information was also missing for 126 adolescents, further limiting the study sample. The small numbers of participants in the groups classified as “excess weight and normal body fat percentage” reduced the precision of some estimates. The dosing of inflammatory markers with Milliplex presents some limitations related to stability, specificity, and possible cross reactions between reagents. Since this was a cross-sectional study, it was not possible to establish a causal relationship between the study groups and their biomarkers.

The study’s strengths were the use of air displacement plethysmography, one of the most valid methods for measuring adiposity, and the use of various biomarkers to assess cardiovascular and inflammatory risk in adolescents, including biomarkers related to low-grade inflammation, such as IL-6, TNF-α, and CRP ¹⁵15. Pahwa R, Jialal I. Chronic inflammation. Treasure Island: StatPearls; 2018., and to more intense inflammatory processes, namely IFN-γ, IL-17, IL-4, and RANTES ¹⁶16. Chehimi M, Vidal H, Eljaafari A. Pathogenic role of IL-17-producing immune cells in obesity, and related inflammatory diseases. J Clin Med 2017; 6:68.^,1717. Mikolajczyk TP, Nosalski R, Szczepaniak P, Budzyn K, Osmenda G, Skiba D, et al. Role of chemokine RANTES in the regulation of perivascular inflammation, T-cell accumulation, and vascular dysfunction in hypertension. FASEB J 2016; 30:1987-99.^,1818. Asadikaram G, Ram M, Izadi A, Fathollahi MS, Nematollahi MH, Najafipour H, et al. The study of the serum level of IL4, TGF ß, IFN?, and IL6 in overweight patients with and without diabetes mellitus and hypertension. J Cell Biochem 2019; 120:4147-57. and cardiovascular diseases, such as VEGF and HFG ¹⁹19. Karaman S, Leppanen VM, Alitalo K. Vascular endothelial growth factor signaling in development and disease. Development 2018; 145:dev151019.^,2020. Visiedo F, Bugatto F, Carrasco-Fernandez C, Saez-Benito A, Mateos RM, Cozar-Castellano I, et al. Hepatocyte growth factor is elevated in amniotic fluid from obese women and regulates placental glucose and fatty acid metabolism. Placenta 2015; 36:381-8..

Few studies were identified that analyzed all the groups considered in the current study. Martinez et al. ⁴4. Martinez KE, Tucker LA, Bailey BW, LeCheminant JD. Expanded normal weight obesity and insulin resistance in US adults of the National Health and Nutrition Examination Survey. J Diabetes Res 2017; 2017:9502643., in 5,983 American adults 20 to 84 years of age, found the following prevalence rates: “normal weight obesity” 4.5%; “excess weight with adequate body fat percentage”, 18%; and “excess weight with high body fat percentage”, 45.5%. Berg et al. ³3. Berg CM, Strandhagen E, Mehlig K, Subramoney S, Lissner L, Björck L. Normal weight adiposity in a Swedish population: how well is cardiovascular risk associated with excess body fat captured by BMI? Obes Sci Pract 2015; 1:50-8., in 3,016 Swedes 25 to 74 years of age, observed the following prevalence rates for men and women, respectively: “normal weight obesity”, 10% and 8%; “excess weight with adequate body fat percentage”, 5% and 4%; and “excess weight with high body fat percentage”, 59% and 44%. In these two studies, the prevalence rates for “excess weight with high body fat percentage” were higher than in our study, which was expected since the populations in those studies were older. However, although our study was done in a younger population, the “normal weight obesity” levels were similar to the prevalence rates in studies done in adults and the elderly.

This finding is worrisome, since “normal weight obese” adolescents presented lower mean muscle mass and were more sedentary. Jean et al. ²¹21. Jean N, Somers VK, Sochor O, Medina-Inojosa J, Llano EM, Lopez-Jimenez F. Normal-weight obesity: implications for cardiovascular health. Curr Atheroscler Rep 2014; 16:464. state that “normal weight obesity” is related to reduced muscle mass, leading to lower energy expenditure since there is less metabolically active tissue, besides involving metabolic deregulation and worse aerobic conditioning.

A comparison of our data with the results reported by Berg et al. ³3. Berg CM, Strandhagen E, Mehlig K, Subramoney S, Lissner L, Björck L. Normal weight adiposity in a Swedish population: how well is cardiovascular risk associated with excess body fat captured by BMI? Obes Sci Pract 2015; 1:50-8. shows that girls presented a higher percentage of “normal weight obesity”, while boys had more “excess weight with adequate body fat percentage”. Girls tend to exhibit higher body fat percentage due to genetic and hormonal factors ²²22. He Z, Rankinen T, Leon AS, Skinner JS, Tchernof A, Bouchard C. Plasma steroids, body composition, and fat distribution: effects of age, sex, and exercise training. Int J Obes 2018; 42:1366-77.. Meanwhile, boys tend to show a higher proportion of “excess weight with adequate body fat percentage”, possibly since they have more muscle mass and practice more physical activity on average ²³23. Schorr M, Dichtel LE, Gerweck AV, Valera RD, Torriani M, Miller KK, et al. Sex differences in body composition and association with cardiometabolic risk. Biol Sex Differ 2018; 9:28..

Another relevant result was that “normal weight obese” adolescents showed higher total cholesterol and LDL-cholesterol, and those with “excess weight and high body fat percentage” had worse values for triglycerides and HDL-cholesterol. These findings may be due to excess body fat percentage and the fact that the mean values were similar in the groups with “normal weight obesity” and “excess weight with high body fat percentage”. Serrano et al. ⁵5. Serrano HMS, Carvalho GQ, Pereira PF, Peluzio MCG, Franceschini SCC, Priore SE. Composição corpórea, alterações bioquímicas e clínicas de adolescentes com excesso de adiposidade. Arq Bras Cardiol 2010; 95:464-72. studied 113 female schoolchildren 14 to 18 years of age in Minas Gerais, Brazil, and found that adolescents with “normal weight obesity” and “excess weight with high body fat percentage” had a worse lipid profile than their “normal weight” peers. The authors expressed their concern that the pathogenesis of atherosclerosis correlates with lipid levels in this life phase. They further warned that even with adequate BMI, high body fat percentage can contribute to the development of chronic noncommunicable diseases which, if present since adolescence, can be exacerbated in adulthood.

High body fat percentage is also implicated in chronic low-grade inflammation involving an increase in inflammatory cytokines and acute-phase proteins, such as IL-6, TNF-α, and CRP, which are classic inflammatory mediators ²⁴24. Engin A. The pathogenesis of obesity-associated adipose tissue inflammation. In: Engin AB, Engin A, editors. Obesity and lipotoxicity. Cham: Springer; 2017. p. 221-45..

The current study found a difference between groups in IL-6 and CRP levels, but no difference in TNF-α values. The adolescents did not show differences in IL-6 concentrations between the groups with “excess weight and high body fat percentage” or “normal weight obesity”. However, IL-6 was higher in these two groups when compared to “normal weight” individuals, indicating that IL-6 was more related to high body fat percentage. Schlecht et al. ²⁵25. Schlecht I, Fischer B, Behrens G, Leitzmann MF. Relations of visceral and abdominal subcutaneous adipose tissue, body mass index, and waist circumference to serum concentrations of parameters of chronic inflammation. Obes Facts 2016; 9:144-57., in 97 Germans 22 to 69 years of age, observed that the associations between visceral adipose tissue and IL-6 were stronger than between BMI and IL-6, indicating that adipose tissue can furnish metabolic information captured by IL-6 that is not captured by BMI.

Adolescents with “excess weight and high body fat percentage” and “excess weight and adequate BFP” showed the same concentrations of CRP, and these concentrations were higher than in “normal weight” individuals. Thus, higher concentrations of CRP in this study were related to obesity indicated by BMI and not to high body fat percentage. Different results appeared in a study of 3,483 individuals 22 years of age in Pelotas in which obese individuals (both according to BMI and high body fat percentage) had higher IL-6 and CRP values ²⁶26. Menezes AMB, Oliveira PD, Wehrmeister FC. Association between interleukin-6, C-reactive protein and adiponectin with adiposity: findings from the 1993 Pelotas (Brazil) birth cohort at 18 and 22 years. Cytokine 2018; 110:44-51..

Studies have reported a positive correlation between IL-6 and CRP and high body fat percentage. When adipocytes increased, their secretory properties are altered, elevating the levels of circulating CRP and IL-6. These cytokines are associated with worse cardiovascular outcomes and play an important role in all stages of atherosclerosis, from onset of progression to the rupture of atherosclerotic plaques ²⁵25. Schlecht I, Fischer B, Behrens G, Leitzmann MF. Relations of visceral and abdominal subcutaneous adipose tissue, body mass index, and waist circumference to serum concentrations of parameters of chronic inflammation. Obes Facts 2016; 9:144-57..

“Normal weight obese” adolescents showed higher IL-6 levels, but not higher CRP. IL-6 is the principal interleukin that stimulates the CRP release in the liver, which does not rule out the future possibility of higher CRP values in “normal weight obese” adolescents if the same exposure characteristics are maintained, since altered IL-6 occurs first, followed later by altered CRP ²⁷27. Eklund CM. Proinflammatory cytokines in CRP baseline regulation. Adv Clin Chem 2009; 48:111-36..

One intriguing finding was the similar CRP value between adolescents with “excess weight and adequate body fat percentage” and “excess weight and high body fat percentage”. The fact that CRP in this study was related to obesity measured by BMI and not by elevated body fat percentage in these two groups may be because these adolescents presented other risk factors for elevated CRP, such as stress, smoking, medications, alcohol abuse, and inadequate diet, and not necessarily increased adipose tissue ²⁸28. Wensley F, Gao P, Burgess S, Kaptoge S, Di Angelantonio E, Shah T, et al. Association between C reactive protein and coronary heart disease: Mendelian randomisation analysis based on individual participant data. BMJ 2011; 342:d548..

Adolescents with “excess weight and adequate body fat percentage” were also those with the highest muscle mass values and the highest rates of moderate and high physical activity. Kasapis & Thompson ²⁹29. Kasapis C, Thompson PD. The effects of physical activity on serum C-reactive protein and inflammatory markers: a systematic review. J Am Coll Cardiol 2005; 45:1563-9. reported that immediate and short-term physical exercise produces an inflammatory response, since exercise-induced muscle injury causes a repair response, stimulating higher production of CRP. Thus, adolescents with “excess weight and adequate body fat percentage” may have been starting some physical activity program when the data were collected.

This study did not find significant differences between the groups for IFN-γ, IL-17, IL-4, VEGF, HFG, and RANTES. Besides the classic cytokines mediating the inflammatory process in obesity, IFN-γ, IL-17, IL-4, and RANTES also participate in the inflammatory process. However, they have been studied less frequently as possible inflammatory markers of obesity, and generally in older populations. Sumarac-Dumanovic et al. ³⁰30. Sumarac Dumanovic M, Stevanovic D, Ljubic A, Jorga J, Simic M, Stamenkovic Pejkovic D, et al. Increased activity of interleukin 23/interleukin 17 proinflammatory axis in obese women. Int J Obes 2009;33:151-6. studied 46 women 20 to 52 years of age in Serbia, and in keeping with our findings, they did not find higher IFN-γ levels in obese women according to BMI when compared to “normal weight” women. Still, these same authors found that IL-17 concentrations were higher in obese women, independently of the increase in abdominal adiposity, insulin resistance, and leptin.

RANTES is a chemokine related mainly to atherogenesis ³¹31. Versteylen MO, Manca M, Joosen IA, Schmidt DE, Das M, Hofstra L, et al. CC chemokine ligands in patients presenting with stable chest pain: association with atherosclerosis and future cardiovascular events. Neth Hear J 2016; 24:722-9.. Koh et al. ³²32. Koh SJ, Kim JY, Hyun YJ, Park SH, Chae JS, Park S, et al. Association of serum RANTES concentrations with established cardiovascular risk markers in middle-aged subjects. Int J Cardiol 2009; 132:102-8. observed an association between serum RANTES concentrations and cardiovascular risk markers in a case-control study in 302 men 40 to 65 years of age. Records show that this chemokine’s concentrations are elevated in the presence of obesity ³³33. Saukkonen T, Mutt SJ, Jokelainen J, Saukkonen AM, Raza GS, Karhu T, et al. Adipokines and inflammatory markers in elderly subjects with high risk of type 2 diabetes and cardiovascular disease. Sci Rep 2018; 8:12816..

Our study did not find a difference between the groups’ VEGF and HFG, which are growth factors secreted by adipose tissue. Contrary to our findings, some epidemiological studies suggest that increased VEGF levels are associated with obesity ³⁴34. Makey KL, Patterson SG, Robinson J, Loftin M, Waddell DE, Miele L, et al. Increased plasma levels of soluble vascular endothelial growth factor receptor 1 (sFlt-1) in women by moderate exercise and increased plasma levels of vascular endothelial growth factor in overweight/obese women. Eur J Cancer Prev 2013; 22:83-9.. However, a study by Azizian et al. ³⁵35. Azizian M, Mahdipour E, Mirhafez SR, Shoeibi S, Nematy M, Esmaily H, et al. Cytokine profiles in overweight and obese subjects and normal weight individuals matched for age and gender. Ann Clin Biochem 2016; 53:663-8. (2016) with 242 Iranians did not find a significant difference in VEGF levels between obese and non-obese individuals according to BMI. Rehman et al. ³⁶36. Rehman J, Considine RV, Bovenkerk JE, Li J, Slavens CA, Jones RM, et al. Obesity is associated with increased levels of circulating hepatocyte growth factor. J Am Coll Cardiol 2003; 41:1408-13. found that circulating levels of HGF, but not of VEGF, were significantly correlated with BMI in 65 persons 32 to 41 years of age in Indiana, USA. Bell et al. ³⁷37. Bell LN, Ward JL, Degawa-Yamauchi M, Bovenkerk JE, Jones R, Cacucci BM, et al. Adipose tissue production of hepatocyte growth factor contributes to elevated serum HGF in obesity. Am J Physiol Endocrinol Metab 2006; 291:E843-8. observed that increased HGF secretion may result from post-transcriptional events, possibly related to the size of adipocytes and elevated TNF-α stimulus in the adipose tissue in 29 obese individuals 45 to 49 years of age.

The absence of differences between this study’s groups for TNF-α, IFN-γ, IL-17, IL-4, VEGF, HFG, and RANTES may be due to the fact that these biomarkers are not as sensitive to the origins of inflammatory problems, when compared to IL-6 and CRP, as well as to the fact that this study’s population consisted of young people (18-19 years), while the studies assessing the other biomarkers were performed in older populations.

This study found that adolescents with “excess weight and high body fat percentage” had worse lipid and inflammatory profiles. Some adolescents also had high body fat percentage despite normal BMI, with higher levels for some lipid profile parameters. BMI thus exhibits important limitations as a method for assessing obesity status, since it does not distinguish between body compartments, and the use of this indicator alone is insufficient for assessing obesity in adolescents. It is thus pertinent to perform a more precise assessment, including biomarkers, mainly IL-6 and CRP, and considering body fat in order to adequately monitor individuals for health risks or problems related to high body fat percentage and with increased risk of developing inflammatory, atherosclerotic, and cardiovascular diseases.

Acknowledgments

The authors wish to acknowledge the Department of Science and Technology of the Brazilian Ministry of Health (DECIT) and the Brazilian National Council for Scientific and Technological Development (CNPq) for their financial support.

References

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