The Nutrition Debate #170: Your instinctive “appetite for protein”

A new study from the University of Sydney’s Charles Perkins Centre, published online in Obesity Reviews, “shows the overriding drive for dietary protein could be a key factor in the global obesity epidemic,” the release said. It hypothesizes that, “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.”

The study “…collated the results of 38 published experimental trials measuring the unrestricted energy intake of people on different diets, also taking into account a broad spectrum of age ranges, BMIs, and diet durations,” the release said.

“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 than you should,” said Dr. Alison Gosby, lead author. “As diets shift toward an increased proportion of foods that are higher in carbohydrates or fat, available protein is reduced and energy intake necessarily increases.” This is reminiscent for me of a theory propounded by the Jaminets in their Perfect Health Diet. It is in Chapter 17, “Nutrient Hunger: A Key to Weight Loss,” starting on page 174 of their very good book.

Two more quotes: “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,” Dr. Gosby said (emphasis mine).

So the hypothesis is, “does your metabolic drive for protein cause you to eat too much “energy”? To explore that question, we first need to define “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 because, unfortunately, the body has no way to store it.

 Carbohydrates and fat are the body’s main sources of energy. The body is designed to use carbohydrates first, both in the form of glucose stored primarily in the liver and muscles as glycogen, and from the carbohydrates we eat, both sugars and starches, which digest to glucose and are circulated and burned directly for energy. So long as the body has carbs available, either stored or from food, it will use carbs for energy and store any excess carbs as glycogen or fat and any fat eaten as 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 craves more by making us feel “hungry.” Carbs, by design, are the body’s first source of energy. The body’s metabolic mechanism wants to save stored energy for when carbs are not available, as while we sleep (if we’re ketogenic), or for days or weeks or months when food sources are (or rather were) scarce or non-existent. Unfortunately, or rather fortunately from a survival perspective, in our world today, scarcity of carbohydrates is a virtually unknown phenomenon.

But, when glycogen energy stores are used up, and we eat very few carbohydrates, the body naturally transitions to using fat for energy. It will do this in combination with a low carb intake, or even without any ingested carbohydrates at all, making the very limited amount of glucose the body needs for cells that don’t have mitochondria. Glucose is so essential, in these small amounts, that the body has devised multiple ways to make glucose in the absence of eating carbs or having stored glycogen. Among the ways are gluconeogenesis, a process whereby the liver makes glucose from excess amino acids from digested protein that have been stored there. Another way is by combining the glycerol molecules freed up when a triglyceride, circulating in the blood or stored as a fat cell, is catabolized (broken down) and oxidized (burned) for energy. The body also makes ketone bodies as a byproduct of fat breakdown, and ketone bodies are ideal food for the brain.

Thus, both protein and fat, either ingested as food, or stored in muscle, liver or fat, can be used to make glucose. That’s how important glucose is to the body. If you don’t eat carbohydrates, which break down to glucose, the body will make glucose. I’m not saying you shouldn’t eat carbs. I’m just saying the body is designed to make glucose if you don’t.

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

That’s not only natural, it desirable. Both you, who want to lose weight without hunger, and your body, which needs energy and is happy to be burning fat for energy when carbs are all used up or not available, will be in homeostatic balance so long as you have body fat reserves to use, and you don’t eat too much fat so it needs to go to your fat reserves for energy.

So, what amount of protein (percent, not grams) will satisfy our instinctive appetite for protein? This is essential to know if that percent protein is the driver for overeating either carbohydrates or fat. The answer is revealed in my next post, #171.