Body Mass Index, Adipose Tissue, and Resting Metabolic Rate Could Be Affected by Age at Onset of Obesity in Overweight and Obese Adult Women

Background: Obesity is introduced as one of the chronic diseases in most of the countries. In fact, 75 to 80% of obese youngsters will remain obese in adulthood. This study as a novel one was conducted to evaluate the possible association between the age at onset of obesity and body composition as well as Resting Metabolic Rate (RMR) in overweight and obese adult women. Methods: A total of 295 overweight and obese women aged 18-50 years were enrolled in this cross-sectional study. Over the past year, dietary intake and nutritional status were evaluated using a semi-quantitative Food Frequency Questionnaire (FFQ) including a list of 147 food items. An impedance fat analyzer (InBody 720, Korea) was used to obtain the body composition and an indirect calorimeter was applied to assess the RMR. T-test was used to compare the means of two groups at onset of obesity for quantitative variables, while multiple linear regression was used to assess the relationship between the age at onset of obesity with body composition and RMR. Results: The results of our study showed that subjects in the upper age group at onset of obesity had lower RMR (p=0.02) and age (p≤0.001) than those in the lower age group. The outcomes showed that an earlier onset of obesity was significantly associated with higher body weight (Beta: -0.11, CI: -0.30 to -0.00, p=0.005) and fat mass (Beta: -0.13, CI: -0.23 to -0.01, p=0.02). After adjustment for confounders including age, physical activities, and total energy intake, those differences still remained significant. Furthermore, RMR per body weight became significant too (Beta: 0.16, CI: 0.00 to 0.11, p=0.03). Conclusion: The results of the present study demonstrated a direct association between the age at onset of obesity and RMR per body weight, but it was inversely related to body weight and fat mass. Prospective studies are needed to confirm these findings.