Why can't we control our food intake? The downside of dietary variety on learned satiety responses.

A striking feature of the modern food environment is the sheer amount of dietary choice available to the individual. In addition to an endless variety of highly palatable and energy dense foods, efforts to combat obesity have resulted in the production of several low- and reduced-calorie versions of these foods that are marketed to consumers. As a result, we are now confronted with a staggering amount of 'dietary variability'-the same food item can be obtained in a variety of different energy densities. This is a concern because evidence in rodents suggests that this kind of dietary variability can compromise one of the major cognitive determinants of food intake among non-human animals-flavor-nutrient satiety learning. Flavor-nutrient satiety learning enables animals to learn about the energy content or satiating quality of the foods they consume and adjust their intake to fit their energy needs. Notably, evidence suggests that dietary variability can disrupt this kind of learning, leading to overeating and weight gain. Here, I discuss the utility of flavor-nutrient satiety learning in human dietary behavior, highlighting certain features of the modern environment that can be disruptive to the acquisition of this kind of learning in humans. Special emphasis is placed on dietary variability, however I also highlight other aspects of the environment that can undermine this kind of learning, such as competition from other satiety-relevant cues (i.e., food labels), detrimental effects of Western diets on food-related cognitive processing, and the abundance of macronutrients that are inadequate at supporting learned satiety responses. The goal of this work is to highlight novel ways in which the environment may disrupt food-relevant learning and energy intake, and to provide some explanation for the elusive nature of flavor-nutrient learning in humans.