In a study published in this issue of the Journal, Buckley et al. (1) develop a computerized task to measure macronutrient valuation that they define as the “value that humans place on a calorie derived from fat, carbohydrate, and protein.” In the same paper, they then use the new method to explore how protein valuation correlates with body composition in a separate sample of community-dwelling elderly. The authors suggest that macronutrient valuation is a driver for food preference that might contribute to explaining food choices. According to this framework, preference for highly palatable and sweet foods might for instance result from a higher valuation of carbohydrates and fats, whereas higher protein valuation might explain preference for foods that are rich in protein. Studying protein valuation from this point of view is of particular interest: although our capacity to choose high-protein containing foods is essential for health, we cannot rely on a consciously perceptible sensory stimulus, as is the case with texture for fat (2) or sweet taste for sugars. Indeed, despite evidence about the red color (3) or umami taste (4) being markers of dietary protein, there is no specific sensory characteristic that is shared among all high-protein containing foods. Therefore, it is more likely that our ability to choose dietary protein sources is based on conditioning that occurs throughout our life when we experience association between consumption of specific foods (here, sources of dietary protein) and beneficial nutritional outcome (here, suppression of amino acid depletion). Although precise mechanisms that lead to such conditioning remain to be discovered, studies in rodents and humans demonstrate that animals compose their diet in a way to ensure sufficient protein intakes, and a diet that is depleted in protein or essential amino acids provokes aversion and lower intakes as a result of experienced metabolic distress (5). In a natural setting, measure of protein valuation could thus be a useful method to explore how humans choose dietary sources of protein for their diet.