There seem to be two major camps in the diet wars: low fat and low carb. In the former people go out of their way to buy skinless chicken and fat-free dairy and their omelets are made from egg whites only. In the latter people are adding heaping spoonfuls of butter and coconut oil to their coffee or tea in an effort to eat more fat. The macronutrient that gets ignored—with powerful yet underappreciated effects—is protein. Patients who restrict calories throughout the day and then find themselves diving head-first into a half gallon of ice cream late at night or who try to fill up on foods that ultimately offer little satiety—lettuce rice cakes granola bars carrot sticks—and who beat themselves up for their seemingly out-of-control junkfood cravings might benefit from learning about the protein leverage hypothesis.

Stated most simply “the protein leverage hypothesis (PLH) predicts that humans prioritize protein when regulating food intake.” In plain English protein leverage speculates that we are driven to consume food until we meet our minimum protein or amino acid needs. The real-world implication is that if we don’t consume adequate protein we will overconsume foods high in carbohydrates and/or fats in a subconscious effort to obtain those critical amino acids. As one nutritionist and science writer put it “the amount of protein you eat could determine the total energy consumption since the appetite for protein is so strong that we keep eating until we get to our target protein intake. If we eat an unbalanced diet that contains a low percentage of protein we increase the total energy ingestion in order to get to our target protein intake.” (Is this why it’s so easy for some of us to polish off an economy-sized bag of chips or cookies in one sitting but if we’ve had an enormous steak or pork chop we don’t exactly want to scarf down three or four more?)

The word “percentage” is particularly important with regard to protein. Recommendations for protein intake on various diets tend to be given as percentages—for example 15% of total calories or 30% of total calories (the latter as called for in the popular “Zone” diet.) However going by percentages may lead people to unintentionally underconsume protein. Guidelines for protein intake should ideally be based on an individual’s lean mass and be given in absolute grams rather than as a percentage of total energy intake. Or if we do continue to refer to percentages many healthy hunter-gatherer populations consumed diets of 19-35% protein “at the expense of carbohydrates” at about 22-40% of total calories—putting their protein intake substantially higher and their carbohydrate intake substantially lower than what many people in North America consume today. (High protein diets with a low carbohydrate content reduce hunger and total energy intake more than high protein diets with a medium carbohydrate content at least in the short term.) 

Recommendations employing absolute grams are typically in the range of 0.8-1.0 grams of protein per kilogram of body weight per day. But some researchers who specialize in protein metabolism muscle tissue dynamics and physical activity believe that current protein guidelines fall short for many people—older individuals in particular. It should be emphasized that 0.8-1.0 grams per kilogram is perhaps a minimum based on nitrogen balance studies. It is not intended to provide an optimal protein intake for all individuals. Some may find they fare better—in overall physical and psychological health and wellbeing as well as regarding body composition—with significantly more dietary protein.

According to the Food and Nutrition Board of the Institute of Medicine of the US National Academies of Sciences the acceptable range for protein intake as a percentage of total calories for adults is 10-35%. The upper range is quite a bit higher than the 12-15% of calories so often recommended. Researcher Stuart Phillips PhD wrote that this acceptable macronutrient distribution range for protein “is a tacit endorsement that protein intakes at levels higher (much higher) than the RDA are associated with good health.” He cites data indicating “that even minimal protein requirements for healthy young men (and presumably women) should be 1.0 g/kg/day and as high as 1.2 g/kg/day.” And remember those are minimums. Optimal intake could well be higher as Don Layman PhD stated the case for in an insightful lecture. Other researchers concur “that protein requirements have been significantly underestimated.”

If it’s true that humans (and other animals) will continue to ingest energy until they’ve met their protein/amino acid requirements this could be a major contributor to obesity and other sequelae from metabolic dysregulation. The following abstract from a paper by David Raubenheimer and Stephen Simpson—who coined the term “protein leverage”—is telling:

“The obesity epidemic is among the greatest public health challenges facing the modern world. Regarding dietary causes most emphasis has been on changing patterns of fat and carbohydrate consumption. In contrast the role of protein has largely been ignored because (i) it typically comprises only approximately 15% of dietary energy and (ii) protein intake has remained near constant within and across populations throughout the development of the obesity epidemic. We show that paradoxically these are precisely the two conditions that potentially provide protein with the leverage both to drive the obesity epidemic through its effects on food intake and perhaps to assuage it.”

Ignatius Brady MD wrote a fascinating popular article on protein leverage where the following gems can be found: 

• “The idea of ‘leverage’ is used to explain the fact that small changes in protein availability can trigger large changes in animal behavior. When protein becomes less available fruit flies will hold off on mating humans will overeat and crickets will become cannibals.”
• “If we don’t consciously seek out protein and instead eat freely from the available food supply we are in essence forced to over-consume fat and carbohydrate calories to reach our protein goal.”
• “Because protein has been diluted by carbohydrate in the modern food supply we must eat more carbohydrate to gain limited protein. Because food is so easy to obtain for most of us we’ve made the switch to these lower protein foods at the expense of a couple hundred extra calories a day without noticing much has changed... except of course our weight which we’ve sort been puzzled about but not too puzzled to stop seeking the nutrients we need.” 

In terms of total energy intake consuming protein-rich foods gives us more protein than if we were to try and get the same amount of protein from a protein-dilute food. In an effort to simply meet our metabolic and physiologic needs we might consume potentially hundreds of extra calories without intending to. We can only white-knuckle cravings and fight our innate drives for so long. In the end biology always wins. Perhaps the next time a patient mentions that he or she can’t stop snacking late at night—or maybe all throughout the day—ask them to think about how much protein they’ve had. If they’ve been skimping on this critical macronutrient they might find their appetite and cravings are tamed if they make a deliberate effort to eat more protein.