Several studies have looked at the relationship between 25-hydroxyvitamin D [25(OH)D] levels and insulin resistance in the overweight and obese population, but the results have varied. Many studies found that low 25(OH)D levels in subjects affected by obesity were associated with insulin resistance or the presence of metabolic syndrome, but several studies have not found these associations. A retrospective chart review was conducted in outpatient medical records from the Nutrition and Weight Management Center at Boston Medical Center. Subjects (n=191) had an average BMI of 43. Results showed that 25(OH)D levels were inversely correlated with BMI, body weight, waist circumferences, and HbA1c levels but not with blood pressure, total cholesterol, high-density lipoprotein cholesterol, triglycerides, or low-density lipoprotein cholesterol. This suggests that vitamin D levels are related more to adiposity than other indicators of health status.

There have been many studies conducted on the effects of weight loss on energy expenditure, but little is known about the effects of overeating on energy expenditure. A study was conducted to examine the daily changes in activity during overfeeding with diets that differed in dietary protein because it has been previously observed that differences in adaptive thermogenesis exist among low- (five percent), normal- (15 percent) and high (25 percent) dietary protein intake. Results showed that activity-related energy expenditure (AREE) measured from doubly labeled water, percent activity, and spontaneous physical activity (SPA) in the metabolic chamber increased with overfeeding, but SPA was no longer significant after adjusting for changes in body composition. Change in AREE was positively correlated with weight gain but not protein intake. This study suggests that overeating causes an increase in physical activity, which supports the idea that adaptive thermogenesis occurs in response to weight gain.