Unhappy meal: how our need to detect stress may have shaped our preferences for taste.

Conventional wisdom says that our preferences for particular tastes evolved to ensure an adequate instinctual intake of metabolic resources. Yet we discern scant taste in many vital dietary components, such as vitamins, minerals, co-factors, essential fatty acids and amino acids. We propose that taste preferences evolved to serve a secondary function--that of xenohormesis. Stress causes organisms to convert complex sugars to simple sugars, as seen during fruit ripening, and to increase the proportion of high-energy saturated fats relative to unsaturated fats, as seen among farmed livestock. The presence of dietary simple sugars, saturated fats, and salt within an organism may echo its stress experience--an experience assimilated by others when consumed. As each successive consumer in the food chain incorporates the stress phenotypes of its dietary components, cues for stress may accumulate in a game of "you-are-what-you-eat". Detection of environmental stress embedded in diet may promote adaptive phenotype remodeling such as caloric hoarding to contend with potential ecologic challenges. The phenotype remodeling may be the result of direct stress signaling properties of fats, sugars, and salt. Since food ecosystems typically exhibit seasonality in composition, early detection of cues of ecologic stress during autumn, such as dehydration, lowered ambient temperatures, and impending resource scarcity, likely confers advantages in fitness. Taste preferences may represent a form of "Darwinian rubbernecking. Much like paying attention to vignettes of violence and trauma, recognizing proxies of ecologic stress and adapting accordingly may yield fitness advantages. Many aspects of agricultural modernization may increase the level of stress embedded in the food chain, catering to pre-existing taste preferences in a form of illegitimate signaling. Globalization and technology have transformed the dietary experience of autumn--when the food chain undergoes stress and therefore tastes the best--into a year-round bacchanal. Instead of experiencing ecologic stress through their diet in a seasonal pattern, modern humans have become creatures of chronic stress. Many human conditions related to stress dysfunctions may partly arise from maladaptive consumption of stressed foods. We anticipate that low-stress and stress-free food may have therapeutic potential in the treatment of diseases and the promotion of health.