Is obesity the next step in evolution through brain changes?

Obesity is a disease of complex and multifactorial nature characterized by the interplay of genetic and environmental factors. The prevailing consensus suggests that obesity arises from an imbalance in energy homeostasis, largely driven by excessive consumption of a high-caloric diet and insufficient physical activity. Over time, therapeutic interventions have traditionally focused on addressing this energy imbalance, as well as the medicalization of all types of obesity. However, there is an alarming increase in the prevalence of obesity, reaching pandemic proportions, with significant consequences for the health of a substantial part of the global population, undoubtedly necessitating a change in strategy. Our purpose is to analyze the obesity pandemic from an evolutionary perspective, and review how its social and cultural causes interact with its pathophysiological determinants. Thus, the culture-brain co-evolution hypothesis is proposed as a compelling framework within niche construction theory that acts as an evolutionary driver for brain expansion and physiological changes in the human species. Some cultural innovations as the invention of tools, and the adoption of processed and cooked foods, have enabled greater energy intake and improved nutrient quality for human diets. These behavioral changes results in the expansion and growth of the human brain, while simultaneously reconditioning the digestive apparatus, leading to a shortening in the time dedicated to foraging and food digestion. These adaptations may have been favored by natural selection, promoting the survival and reproductive success of individuals carrying genetic variants conducive to brain growth and to shape our evolutionary trajectory. In the 20th and 21st centuries, the obesogenic environments were placed in our lifestyles, characterized by extreme sedentary behaviors and the spread of highly processed and high-energy diets. These evolutionary mechanisms may inevitably contribute to the emergence of a new niche that, in addition to explaining the obesity pandemic, could ultimately lead to the "normalization" of phenotypes and genomes associated with obesity. This phenomenon represents a predictable outcome that derives from our biological predispositions developed over countless generations. Addressing this global challenge necessitates the creation of non-obesogenic environments that promote healthy lifestyles to reduce the prevalence of obesity. The failure to take action could perpetuate the current evolutionary trajectory toward a human species characterized by obesity-related genotypes and phenotypes.