Appetites:
Malnutrition, which includes overnutrition, undernutrition, and imbalanced nutrition, affects at least a third of the earth’s population and is by far the greatest contributor to the global burden of disease. Information about the dynamics of human appetite systems is essential for understanding why we eat the amounts of nutrients and energy that we do. The main conclusion that it presents is by no means obvious: it suggests that humans will overeat fats and carbohydrates not because they have a particularly strong drive to eat these nutrients, but because of a strong appetite for protein. On the other hand, we should not interpret this to suggest that the human appetite is exclusively about protein. Rather, in circumstances where it is possible, the appetites for different macronutrients cooperate to select a balanced diet, but when limits on available foods prevent this, protein regulation overrides and fat and carbohydrate intakes follow more passively. Just as the macronutrients combine in specific proportions in foods, so too do foods combine into meals, meals into diets, and diets into dietary patterns. Although some foods are eaten directly, the greatest portion of the human diet is eaten as mixtures of foods, called meals. Meals, therefore, are important levels of focus for understanding human eating choices. And yet neither foods nor meals are the primary link between nutrition and health; for that we need to consider the long term cumulative intakes of foods and meals, namely, diets. To close the circle, diets impact health and disease principally via their primary components, the nutrients.
Protein:
There is now strong evidence that excess protein intakes are associated with negative cardiometabolic profiles and accelerated aging, especially when coupled with low carbohydrate intakes. Consistent with this is the observation that the healthiest dietary patterns, including the Mediterranean, traditional Okinawan, Kitavan Islanders, and Tsimane diets, are associated with low dietary protein densities and low protein intakes. This should caution against high-protein diets, such as the Atkins, high protein Paleo, and Sugar Busters diets, except as therapeutic interventions for weight loss. It also raises questions about the high end of the protein range sanctioned by the US AMDR. A combination of low protein (60g-ish) and high fiber actually has the double health benefits of limiting protein intake while avoiding energy overconsumption. Another advantage of building such a model is that it provides a context for identifying important aspects of our food environment that might influence the relationships within the model. For example, among the most salient and influential aspects of industrialized food environments is economics, giving rise to the question of whether the cost of foods might play a role in influencing the macronutrient composition of our diets. Results showed that the cost of supermarket foods is positively related to their protein content. In this way, protein leverage might help to explain the well-established association between lower socioeconomic status and obesity. We might likewise address the question of why the USDA AMDR spans such a wide range of dietary protein densities, encompassing both low-protein diets (10–15% protein), which our model suggests are likely to be associated with excess energy intake, and the high end (25–35%), associated with excess protein intake and premature aging. One possibility is that this reflects influence on research and government policy by the food industry, rather than health considerations. For example, the sugar and affiliated industries selectively sponsor research that casts doubt on recommended upper limits to sugar intake, and the meat, dairy, and egg industries do the same for protein. These industries also exert influence on dietary guidelines through political lobbying that emphasizes the importance of dietary balance. In closing, we emphasize that our main goal is not to suggest that we have solved the problem of energy overconsumption, obesity, and related diseases, but rather to introduce a biologically inspired approach that can help to structure nutrition research. Beyond the macronutrients and their different types and constituents, other dietary components such as fiber and micronutrients clearly are relevant to the problem, and likewise, many nutrient combinations are important for various other aspects of health. We suggest, however, that these relationships are best examined in a framework that is guided by biological theory and which examines the interactions among nutrients rather than considering them separately.
