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Abstract
Fat gain in our United States (US) environment of over-abundant, convenient, and palatable food is associated with hypertension, cardiovascular disease, diabetes, and increased mortality. Fuller understanding of physiological and environmental challenges to healthy weight maintenance could help prevent these morbidities. Human physiological limitations that permit development of obesity include a predilection to overeat palatable diets, inability to directly detect energy eaten or expended, a large capacity for fat storage, and the difficulty of losing body fat. Innate defenses resisting fat loss include reduced resting metabolism, increased hunger, and high insulin sensitivity, promoting a regain of fat, glycogen, and lean mass. Environmental challenges include readily available and heavily advertised palatable foods, policies and practices that make them abundant, less-than-ideal recommendations regarding national dietary macronutrient intake, and a frequently sedentary lifestyle. After gaining excess fat, some metabolic burdens can be mitigated though thoughtful selection of nutrients. Reduced dietary salt helps lower hypertension, less dietary sugar lowers risk of cardiovascular disease and obesity, and reducing proportion of dietary carbohydrates lowers post-meal insulin secretion and insulin resistance. Food intake and exercise should also be considered thoughtfully, as exercise in a fasted state and before the meals raises glucose intolerance, while exercising shortly after eating lowers it. In summary, we cannot directly detect energy eaten or expended, we have a genetic predisposition to eat palatable diets even when not hungry, and we have a large capacity for fat storage and a difficult time permanently losing excess fat. Understanding this empowers individuals to avoid overeating and helps them avoid obesity.
Highlights
This review examines human physiological predisposition to overeat, the mechanism thwarting weight loss, and social and environmental factors that led to the sustained rise of obesity and associated metabolic morbidities worldwide, with a particular focus on the United States of America (USA)
Human evolutionary burdens include a large capacity for fat storage compared to non-human primates, a predilection to overeat palatable diets even when not hungry, a strong preference for sweet and lightly salty foods, and an inability to consciously detect energy eaten or expended
As they gain fat in an environment of over-abundant and convenient “supermarket” food, humans are burdened by the complications of obesity: hypertension, atherosclerosis, hypercoagulability of blood, endothelial dysfunction, coronary vascular issues, kidney and heart disease, and stroke
Summary
This review examines human physiological predisposition to overeat, the mechanism thwarting weight loss, and social and environmental factors that led to the sustained rise of obesity and associated metabolic morbidities worldwide, with a particular focus on the United States of America (USA). The central thesis is presented in a series of five arguments: (1) obesity has serious health and economic consequences and is predominantly driven by overconsumption of food rather than by inadequate contribution of energy expenditure through physical activity; (2) overeating is primarily based on human predisposition for overconsumption of palatable foods, aided by governmental food-supply policies, less-than-ideal institutional recommendations for macronutrient intake, and commercial pressures for the sale of palatable food; (3) the key problem facilitating overeating is human physiological inability to directly detect energy eaten or expended through physical activity; (4) human evolution endowed humans, as opposed to non-human primates, with an impressive capacity for fat storage, and human physiology provides strong metabolic, endocrine, and psychophysical defenses against losses of body mass and stored energy regardless of the starting level of fatness; and (5) an understanding of human physiological limitations permissive to overeating, and of difficulties against reducing body fat levels, exacerbated by societal pressures that facilitate overeating, represent a solution toward prudent selection of quantity and quality of nutrients to prevent obesity or mitigate some of its adverse effects
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