Not getting enough protein keeps you hungry, even if you have enough “calories for energy”. Here’s why.
TL;DR: We need to get “essential” amino acids from our diets in order to stay healthy and not feel hungry. Low-protein diets can leave us feeling hungry and eating more, leading to metabolic imbalance and storing extra fat. (about 8 min read)
Metabolic tips for getting enough protein to avoid over-eating:
Build your nutritional base with protein and fiber first to feel full and get enough vitamins/minerals.
Make sure to eat a variety of plant protein sources to ensure you’re getting all of the essential amino acids.
Stay hydrated and take short movement breaks so that the food you eat gets into your bloodstream and to your brain so your brain knows what nutrients you still need (and if you don’t need to eat more).
We eat in order to nourish our bodies. We feel hungry when we’re undernourished. Which is not necessarily the same thing as not eating enough calories. Our bodies need essential amino acids, fats, and micronutrients (vitamins, minerals) from our diets in order to function properly. If we don’t get enough of these nutrients, we can continue to feel hungry.
Amino acids are the “building blocks” of proteins. When we eat proteins, we break them down into amino acids and then our cells do something with those individual amino acids. All unprocessed foods have some amount of protein in them - yes, even plants! no, dead animal muscle is not the only source of protein!! - because the cells of living things need proteins to survive. Muscles and eggs (from animals) and seeds (beans, legumes, nuts from plants) have higher protein content than other foods that may be mostly fat or starch.
We need to eat dietary protein that contains essential amino acids. There are 20 amino acids used to make all the different proteins in our bodies just like the Roman alphabet has 26 letters that make up all of our words (some bacteria have one or two additional rare amino acids but they don’t really play a role in our life so I’m going to ignore them, if you want to learn more, study microbiology metabolism). Our bodies make about half of these amino acids in-house. We need to get the other half from our diets.
Sometimes foods are called “complete protein sources” because the food contains all the essential amino acids. “Incomplete protein sources” are lacking at least one essential amino acid, which would need to be obtained from another food source. Since other animals have similar protein composition in their muscles as us, their muscles are pretty obvious sources of “complete” protein. With the exception of soy, proteins from plant sources may be “incomplete” proteins. That doesn’t mean plant-based diets are inferior sources of protein! It just means that someone would need to be conscientious of which amino acids are present in which plants, and pair them together to have a “complete protein meal”.
Our bodies won’t function properly if we don’t eat enough essential amino acids. The essential amino acids are (in alphabetical order): histidine*, isoleucine, leucine, lysine, methionine*, phenylalanine, threonine, tryptophan, and valine. Not getting enough of the essential amino acids will stunt growth, impair immune function, slow healing, and contribute to feeling hungry (and possibly over-eating if we keep eating foods that don’t have enough of these essential amino acids).
Low-protein diets make us hungrier and can drive overeating. Our brains respond to signals from our other organs (especially the liver, pancreas, and fat cells) to help us decide if we have enough nutrients and enough energy, or if we need to eat more food. Our brains are great at sensing when something is missing and telling us that we need to eat. Our brains are not so great at telling us what to eat - consciously, we think “I’m hungry” and not “my methionine levels are low”. Since unprocessed foods have a variety of nutrients in them (eg., walnuts have protein, omega-3 fatty acids, AND fiber; chia seeds have protein, fiber, AND iron), a general “please eat more” signal from our brains isn’t really a problem.
Now that we have unprocessed foods that are nutrient-poor, or are fortified with one particular nutrient but are not a well-rounded source of multiple nutrients, a “please eat more” signal from the brain isn’t enough information for us to know if we need more simple carbs to recover from our long run, or if we need more protein to recover from our big lifts, or if we need more of some other nutrient. Because of this, low-protein diets keep our brains looking for those essential amino acids and, if we aren’t paying attention, we can keep eating low-protien foods that don’t satisfy our hunger. This leads to extra fat storage from the extra calories.
High-protein diets can cause stress (metabolic imbalance) in our kidneys if we are dehydrated. Our bodies can’t absorb more ~1g protein per pound body weight (BW) (2.2g protein/kg BW, if you’re using the metric system). Eating more protein than that will mean that your kidneys will have to clear extra nitrogen from your body to maintain nitrogen balance. We use nitrogen as part of proteins (the amino group in an amino acid) and as part of the nucleic acids, DNA and RNA. Excess nitrogens that aren’t part of protein, DNA, or RNA get turned into uric acid - which gets removed from your body as urine. Your kidneys do a lot of work to filter waste out of your blood AND to filter back in nutrients that you still need. For instance, your kidneys will push glucose back into your bloodstream so that you don’t have a drop in BGLs levels every time you pee (some type II diabetes prevention/treatment medications will stop glucose reabsorption to help BGLs fall when you pee). It is easiest for your kidneys to sort out what needs to be removed as waste (uric acid, extra salts, some other wastes) and what needs to stay in your blood (glucose, important proteins, other important micronutrients) when you’re properly hydrated. Being dehydrated stresses our kidneys out and leads to inflammation and reduced kidney function.
Too much dietary protein when we aren’t moving around can also cause metabolic imbalance. Because eating protein also causes insulin to be released into our blood by the pancreas, we can create a situation where there’s too much insulin around even if there’s not an obvious spike in blood glucose levels. Remember that metabolic imbalance is not just having too much glucose in our blood at once - it’s a problem with glucose spikes AND too much insulin creating confusing signals for your organs. A high-protein diet can raise insulin without causing a BGL spike. This is an important point when we’re trying to reduce stress and restore metabolic balance!
So how much protein do we actually need in our diets? We need about ~0.34-0.55g protein/lb body weight, unless we’re training vigorously, training to get big, healing from something, recently lost a lot of blood, and/or are pregnant. In those situations, we need closer to 1g protein/lb BW.
Metabolic tips for getting enough protein to avoid over-eating:
Build your nutritional base with protein and fiber first to feel full and get enough vitamins/minerals.
Make sure to eat a variety of plant protein sources to ensure you’re getting all of the essential amino acids.
Stay hydrated and take short movement breaks so that the food you eat gets into your bloodstream and to your brain so your brain knows what nutrients you still need (and if you don’t need to eat more).
*For my nerds: Methionine is always the first amino acid added when your cells build a new protein, so if we’re methionine-deficient, we can’t make ANY new proteins! There’s a whole system of regulation in your cells build specifically around sensing methionine levels. Histidine is used as both an amino acid incorporated into proteins AND as a signaling molecule used by immune cells! Histidine signaling is part of the allergy response, which is why anti-histamines are used to treat over-ambitious allergic reactions.
Grech, A et al., (2022) Macronutrient (im)balance drives energy intake in an obesogenic food environment: an ecological analysis. Obesity.
Ferraz-Bannitz, R et al., (2022) Dietary Protein Restriction Improves Metabolic Dysfunction in Patients with Metabolic Syndrome in a Randomized, Controlled Trial. Nutrients.
