Date of this Version
As the global obesity epidemic spreads, scientists struggle to understand the biological, cultural, and evolutionary bases for modern fatness. Understanding the contributions of the interaction between physical activity and the endocrine system to regulating metabolism could potentially help people who are overweight or obese in losing weight and illustrate one of the evolutionary pathways that encourages modern obesity. This study used an innovative approach that integrated a lifestyle physical activity and diet questionnaire coupled with endocrine analysis (leptin, osteocalcin) and anthropometric measures in order to create baseline measurements of fit individuals. The mean osteocalcin level was 4201.46 pg/mL and the mean leptin level was 1791.87 pg/mL for participants in this study. For leptin, the levels were significantly lower than that of the general population, especially obese groups. The conclusions from this study contribute to the understanding of what physical fitness looks like from an endocrine perspective, which reinforce the current recommendation to treat obesity with diet and exercise.
The thrifty genotype hypothesis posits that although the modern environment is different from the evolutionary environment, the body is still adapted to a past where it was advantageous to store fat against future food insecurity. Regular physical activity with good nutrition causes a cascade effect for leptin, osteocalcin, and insulin that improves the body’s sensitivity to glucose management and efficacy in metabolic regulation. This study found several statistically significant relationships that corroborate existing paradigms and data. Amongst the most important were a positive relationship between osteocalcin and speed of sound (P = 0.038); a negative relationship between leptin and time spent strength training per year (P < 0.05, R = -0.204) and time spent swimming (P = 0.012, R = -0.263); and a positive relationship between time spent strength training and stiffness index (P = 0.039, R = 0.195) and t-score (P = 0.034, R = 0.202). Some relationships that were expected to be significant were not, possibly due to problems with the hormone assays or with statistical power. Future work remains to be done both on the biochemical front as well as for lifestyle data collection.
Advisor: Daniel Osborne