Study explores how biological and environmental systems regulate body weight

Pennington Biomedical researchers recently investigated the systems of the body that regulate weight, exploring whether our bodies defend an established weight target or if our bodies operate within a broader range of tolerance before biological mechanisms are activated. The paper, titled "Body weight regulation models in humans: insights for testing their validity," which was recently published in Nature Reviews Endocrinology, examined competing body weight regulation models and analyzed how energy intake and expenditure interact to maintain or disrupt weight stability. 

The biological mechanisms of body weight regulation are not completely understood, so the researchers evaluated the theories behind the interaction of these mechanisms within the environment, as it ultimately determines body weight. The standard "set point" theory states that each person has a biologically determined weight and that the body reacts strongly when weight changes go above or below that point. 

The new theory – the "dual-intervention point" – states that instead of a singular body "set point," each person has a lower and upper limit, and that the body only reacts when body weight drops below the lower limit or increases above the upper limit. This model states that between these limits, weight is mostly influenced by lifestyle and environment, rather than the body defending against excessive increases or decreases in weight. 

"Human body weight appears to be regulated by biological mechanisms we still do not fully understand," said Dr. Eric Ravussin, LSU Boyd Professor and Douglas L. Gordon Chair in Diabetes and Metabolism at Pennington Biomedical. "Our analysis highlights the need to rigorously test state-of-the-art technology whether humans defend a single biologically determined set point or whether they operate within upper and lower intervention boundaries. In response to prolonged fasting or overfeeding, these models predict different metabolic and compensatory responses in people with a low body weight compared to those with a higher body weight." 

The importance of evaluating these set point and dual-intervention theories may help to explain why losing weight is so difficult for some people and not others, why some people remain underweight even in today's food-rich environments, and why body weight slowly but steadily increases for adults as they age. The underlying purpose of the study is to understand how weight is regulated, which will influence strategies for preventing and treating obesity. 

In the set point model, a fixed body weight defense point is assumed, with deviations triggering compensatory responses, like changes in appetite or energy expenditure. The dual-intervention point model splits responses into three categories: a strong biological defense against weight loss, a defense against weight gain, and a mid-range response that factors in external influences like behavior or environment. This theory also states that the upper boundary has drifted upward over human evolution. 

The dual-intervention theory proposes that the body likely has biological systems designed to maintain weight within a certain range. It is still unknown what the body intends to preserve by maintaining weight, such as body fat, muscle mass, stored carbohydrates or even the energy status of cells. 

"This analysis offers a useful framework for examining how biological and environmental factors interact to influence body weight," said Dr. Jennifer Rood, Interim Senior Vice Chancellor and Executive Director of Pennington Biomedical. "By comparing set point and dual-intervention models, the research contributes to a clearer understanding of weight stability and weight change. The work by Dr. Ravussin and his colleagues reflects Pennington Biomedical's continued commitment to advancing thoughtful, evidence-based approaches that can inform future clinical research in obesity."