Retrospective #170: Your “instinctive appetite” for protein

Some time ago, I saw an interesting study from the University of Sydney’s Charles Perkins Centre, published in Obesity Reviews. The press release said, the study “shows the overriding drive for dietary protein could be a key factor in the global obesity epidemic.” Further, “Human’s instinctive appetite is so powerful that we are driven to continue eating until we get the right amount of protein, even if it means consuming far more energy than we need.” (bold added)

“We found that regardless of your age or BMI, your appetite for protein is so strong that you will keep eating until you get enough protein, which could mean you are eating much more [non-protein, i.e., carbs and fat] than you should,” the lead author said. “As diets shift toward an increased proportion of foods that are higher in carbohydrates or fat, available protein is reduced and energy intake [from carbs and fat] necessarily increases.”

Two more: “The strength of your nutritional drive for protein is frightening within our nutritional environment, where there are a large number of low-protein foods consumed on a regular basis.” And, “We have shown that when people are trying to lose weight, they need to look at macronutrient composition, not just calories. If you cut your calories but don’t consider protein intake, you’re going to be hungry and your diet won’t be successful.”

So, the hypothesis is, “Your metabolic drive for protein causes you to eat too much “energy”? To explore that question, we first need to clarify “energy” in the context of food. Of the three macronutrients that supply nutrition – carbohydrates, fat and protein – only carbohydrates and fat provide “energy.” Dietary protein is not a source of energy, per se; it breaks down to 21 amino acids, some of which the body can’t make and which are therefore called “essential.” Amino acids are the basic machinery of all cells. We need to eat protein every day.

Carbohydrates and fat are the body’s main sources of energy. The body is designed to use carbohydrates first, both from the carbohydrates we eat and from glycogen, which is glucose stored primarily in the liver and muscles. When carbs, both sugars and starches, are digested, they are converted by the liver to glucose and burned for energy. The excess is stored as glycogen, or if the liver is full of glycogen, convert it to fat. To repeat: So long as the body has glucose available, either from food or stored, it will use it for energy first and store any excess as glycogen or fat.

That is why we have always had such a hard time losing weight when we eat carbs for energy. The body sensibly uses carbs, and signals “hunger” because it can’t access stored fat. The body wants to save stored fat for when carbs, as glucose or glycogen, are not available, as while we sleep (if we’re ketogenic).

But, when glucose and glycogen energy stores are used up, and we eat very few carbohydrates, the body naturally transitions to using fat for energy. When it does this, it continues to make the very limited amount of glucose the body needs for cells that don’t have mitochondria. Glucose is so essential (in small amounts) that the body has devised a couple of ways to do it in the absence of eating carbs or having stored glycogen. One is gluconeogenesis, a process whereby the liver makes glucose from excess amino acids from digested but unused protein stored there. Another is from glycerol molecules freed up when a triglyceride (fat cell) is broken down and used for energy. The body makes ketone bodies as an end product of this breakdown, and ketone bodies are ideal food for the brain.

So, if you don’t eat carbs for energy, the body must rely on fat, both dietary and stored, for energy. That’s good, if you’re trying to lose weight. When your body is burning fat for energy, won’t feel “starved” or “hungry.” You will not get the “craving” message, because your body has transitioned from being a “sugar burner” to a “fat burner.”

That’s not only natural, it’s what you want. You want to lose weight without hunger, and your body wants to be in energy balance. So, providing you don’t eat too much fat, your body will go to your fat reserves for energy.

So, what amount of protein will satisfy our “instinctive appetite”? This is essential to know if protein is the driver for overeating either carbohydrates and/or fat. The answer is revealed in my next post, Retrospective #171.