The Origin of Obesity: Proportional Influence of Metabolic Factors, Dietary Choices, and Physical Activity

Abstract

Three primary factors contribute to the regulation of body weight: metabolic factors, dietary habits, and physical activity, all of which are influenced to varying degrees by genetic traits. Despite recent advancements in our understanding of these factors, the prevalence of obesity in Westernized societies continues to rise. In contrast to instances seen in monogenic animal models and rare genetic syndromes in humans, the predisposition to common forms of obesity likely involves numerous susceptibility genes. These genes contribute to variations in energy requirements, fuel utilization, muscle metabolism, and taste preferences. While recent increases in obesity rates cannot be attributed to changes in the genetic makeup of populations, it is plausible that previously unnoticed genetic variations now play permissive roles in the context of modern societies.

Available data indicates that variations in resting energy expenditure, the thermic effect of food, and fuel utilization exist but are unlikely, by themselves, to fully account for the onset of obesity. As for dietary patterns, the best available trend data suggests that fat and overall energy intake have decreased, not only in this region but in other Westernized countries as well. Paradoxically, the simultaneous trends of declining energy intake and increasing body weight point toward reduced physical activity as the most significant current factor contributing to the escalating prevalence of obesity. Modern existence necessitates a radical departure from previously beneficial energy-conserving dietary and exercise practices.

Recognizing the inherent challenges in adhering to energy-restricted diets within an environment replete with fast food options and social indulgences, it is unlikely that the current trajectory of rising body weight can be reversed solely through recommendations for further reductions in energy intake. Rather, a substantial increase in physical activity levels is likely required in response to an environment that now encourages a more sedentary lifestyle.