More than just calories: how our bodies prioritize one key nutrient.

In science, the journey from a theory to a well-understood fact isn’t always straightforward. It often starts with a hunch – something scientists have noticed but just don’t fully understand yet. That hunch is tested from every angle, again and again. Sometimes for years, sometimes for centuries, until it becomes a model for what’s actually going on. 

For doctors who treat obesity, one of these ever-evolving theories is the “protein leverage hypothesis” or “protein leverage model.” Basically, it argues that appetite isn’t just determined by how much we eat, but by what we eat. We’re hard-wired for protein, and our body doesn’t want to turn that appetite off until it gets enough of it. In other words, when we eat less protein, we tend to eat more of everything else. 

This wasn’t a problem for most of human history. If we didn’t get enough protein, we made up for it with larger quantities of vegetables and grains. But since the 1970s, those protein substitutes have been steadily replaced with over-processed foods high in sugar, carbohydrates, and fats. Not only that, but protein is relatively expensive, while processed foods are not. So in developing areas, this issue can be compounded by poverty. 

To what extent protein leverage has contributed to the obesity epidemic is still unclear. There’s some evidence proving elements of the hypothesis, but nothing that conclusively shows it’s a leading cause. One of the reasons some scientists are skeptical is that the overall percentage of protein in our food supply has risen over the last century. So we’re eating more protein than ever, right?

Kind of. While the overall protein content in our diet has risen, the actual percentage of calories from protein has decreased by 1% due to the even greater rise in available carbohydrates and fats. Researcher Kevin D. Hall recently showed that the 1% decrease actually raises our overall calorie intake significantly. I won’t go into the math here, but his work seems to show that protein leverage may have contributed to as much as a third of the average adult weight gain over recent decades. Of course, it’s not the only contributor. Lifestyle and environment changes play their roles as well. 

What does protein leverage mean for the average person trying to lose weight? Well, it reinforces a fundamental idea: that we should be more mindful of the things we eat. By understanding the sources of our nutrition – especially protein – we may be able to control appetite more effectively. When developing a strategy with your doctor, make sure that healthy sources of protein take center stage. 

As we study the protein leverage model more closely, we’ll understand obesity better. But more importantly, we’ll be able to develop treatment plans that work with our bodies’ natural priorities. By listening to what our bodies tell us, the road to weight loss can be just a little bit easier.