The Brain, the Environment, and Human Obesity: An Evolutionary Perspective on the Difficulty with Maintaining Long-Term Weight Loss

The dramatic increase in obesity within one or two generations cannot possibly be due to a change in genetics. It is the processing, distribution, and availability of foods that have changed, not the brain. For most people, in the presence of pleasant tasting (high calorie) foods, the brain’s reward circuitry overwhelms the satiety signals. For 2 million years, overeating (on the occasional basis when that was possible) had adaptive value, and it has only been since the rise of an omnipresent obesogenic environment that such behavior has become maladaptive, resulting in widespread obesity. Long-term weight loss is, at minimum, a two-part process: (1) initial weight loss and (2) relapse prevention. All weight loss programs (diet, pharmacology, or surgical) work in the short run, but none used alone have proven widely effective in the long term. After initial weight loss, relapse is common because until recently interventions failed to consider our evolutionary history and thus have underestimated the sensory/reward aspects of feeding behavior. Strongly heritable behavioral characteristics that differentiate obesity-prone individuals from others (e.g., food cue responsiveness, satiety responsiveness) have now been identified and can potentially be targeted to help people learn how to better interact with an obesogenic environment