TL;DR: “Protein” is a macronutrient made up of amino acids. There are several amino acids that our bodies can’t make in-house and we have to get them from our diets for our bodies to function correctly. Not getting enough protein encourages over-eating, slows growth and healing, and promotes weight gain. (about 10 min read)

Metabolic tips for eating enough protein:

• Aim for 0.34-0.55g of protein per lb body weight (0.75-1.2g/kg BW) each day. If you’re doing strenuous exercise, recovering from an injury or illness, or are pregnant, aim for ~1g protein/lb BW.

• Spread your protein out over 3-4 meals to maximize how much your body actually uses for muscle growth/recovery.

• Eating too much protein if you aren’t moving around, or if you are dehydrated, can be stressful on your body. Context matters!

What is “protein” and how is it used in our body? When people use the word “protein”, they may be talking about different things. Scientists will say “protein” when they mean the macromolecule made up of amino acids joined together by a peptide bond (the actual definition of “protein”). Some menus will list “protein source” (especially for salad add-ons) when they really mean “dead animal muscle”. I’ve overheard people at gyms talk about whether or not they should add amino acid supplements in addition to their protein powders. (This secretly-not-so-secretly kills me because proteins ARE amino acids! Yes okay sometimes I am listening to a podcast in the rogue rack and sometimes I am listening to bros get biochemistry wrong and that shit STICKS IN MY BRAIN.)

Proteins are macromolecules made up of amino acids. A macromolecule is just a science term for “big molecule”. You’ve probably heard of “macronutrients” and “micronutrients”. A macronutrient is a macromolecule that we eat. The main macronutrients we eat (aka “macros”) are protein, fats, carbohydrates, alcohol, and nucleic acids. Micronutrients are vitamins and minerals that we need to eat for our enzymes to function correctly. Enzymes are a type of protein that does some chemical reaction. The sum of all the chemical reactions, and how they are regulated by our hydration, hormones, and neural signals, is “metabolism”.

Our bodies can only use a certain amount of protein for new cell growth and repair. The rest gets converted to other macromolecules. The amount of protein we need in a day has a lower limit determined by the essential amino acids that we must get from our diet. For the average person (aka, someone not doing strenuous athletic stuff daily), that’s usually 0.34-0.55g protein per lb body weight (or, 0.75-1.2g protein/kg BW). A lot of exercise nutrition and physiology studies will use “kg body weight”, so remember that 1 kg is roughly 2.2 lb if you’re using the English system (which, in America, we are). So a 150 lb person should be eating ~51-83g of protein a day. A 200 lb person should be eating ~68-110g of protein a day. You can do the math for your body weight.

The amount of protein we need also has an upper limit determined by how much our bodies can absorb and incorporate into new cells (eg, muscle cells or healing). This upper limit will be influenced by how much strenuous exercise we’re doing or if we’re healing from something, lost blood recently, or are pregnant. Under these conditions, we can absorb and use about 1g protein per lb body weight a day* (or 2.2g/kg BW/day).

Can we eat all of our daily protein in one meal? No. Your body can only use so much protein at once and the rest is then used in other metabolic pathways. You can’t store amino acids themselves (nitrogen balance, it’s a thing) so you can only use the protein you eat to make new cells. The rest of the protein will be broken down into two parts: (1) an amino group that gets turned into uric acid (a precursor to urine) and (2) a carboxyl group that is used to make carbohydrates (gluconeogenesis, if blood glucose levels (BGL) are low, or glycogen, if BGLs are fine and your body still has room to store glycogen). You should spread your protein out between all of your 3-4 meals (second breakfast is a real meal).

Do you need extra protein in your diet if you are doing strenuous exercise? Does this change when in the day you should eat protein? Yes. Your body still has to balance nitrogen levels and you can’t really use more than 1g protein/lb body weight/day. However, just like with carbohydrate metabolism, the amount and intensity of your movement will determine how much and what type of fuel your body needs. Eat protein and simple carbs before (30-90 min) and after (30-90 min) workouts to maintain energy levels, improve performance, stimulate muscle growth, and speed up recovery/prevent injuries. The amount of protein and simple carbs you need to eat depends on what exercise(s) you’re doing and what your goals are. Talk to a metabolic coach to figure out these nuances and design a diet that’s right for you.

Extra protein that we eat is less likely to be stored as fat than extra carbohydrates that we eat. It is technically possible for extra protein to get converted to glucose, and then for that glucose to get converted to fat, but it would take a whole other set of biochemical processes and use more energy to do this, so turning protein into fat doesn’t really happen in our bodies. Before you start thinking “OH OKAY, if I just eat protein I won’t store fat!”, remember that we never consume one macronutrient in isolation. I don’t care if you only snort whey powder for your meals, eating excess protein is not a magic bullet to fat loss.

Dietary protein still causes an increase in insulin, even if it doesn’t raise blood glucose levels. Eating proteins does cause a rise in insulin. It also causes a rise in another hormone, glucagon, which blocks insulin action (similar to cortisol). Insulin is saying “take glucose out of the bloodstream” and glucagon is saying “ignore insulin”. WTF? Doesn’t this mean that protein causes your body to send two contradictory signals at once? Yes. Yes, it does. Isn’t this metabolic imbalance the very definition of stress?!? Welp. Just when you thought you didn’t need a Ph.D. in metabolism…

High protein diets can be stressful on your body if you aren’t moving around. Your body REALLY wants to keep stable blood glucose levels. So it prepares for two, somewhat opposing situations at once: (1) when you start moving, your body will also release cortisol, which stimulates your liver to put more glucose in the bloodstream by breaking down glycogen or by making new glucose via gluconeogenesis. Some of that protein will be made into new glucose that gets released into your blood to feed your muscles as they move. Both cortisol and glucagon will inhibit other tissues from responding to insulin so that almost all of the glucose made from protein can be used by your muscles. You’re moving a lot, after all, and your muscles need it!

BUT what if you actually aren’t moving and you’re just drinking a soylent at your desk during a mid-afternoon conference call? Now your body is going to be prepared for the second situation: (2) your blood glucose levels are about to rise and your muscles are not going to use that glucose. The rest of your body needs to help take glucose out of the bloodstream to maintain healthy BGLs. Since protein also causes a rise in glucagon, and glucagon messes with insulin signaling, you will have to put out more insulin to get BGLs stable than if there was no glucagon around. Your body is basically hedging its bets that you probably will move, and preparing for that first, but releasing insulin just in case you don’t.

It is important to maintain metabolic balance with dietary protein. Even if excess dietary protein isn’t going to get converted to fat directly, it can create an environment that makes it easier for your body to store carbs as fat and harder to break down fat into energy. Too much cortisol, insulin, protein intake, and/or glucose in the bloodstream are all stressful and lead to inflammation. Which increases the number of growth factors in your system and makes it harder to build muscle or lose weight. Balance is important and context matters!

Metabolic tips for eating enough protein:

• Aim for 0.34-0.55g of protein per lb body weight (0.75-1.2g/kg BW) each day. If you’re doing strenuous exercise, recovering from an injury or illness, or are pregnant, aim for ~1g protein/lb BW.

• Spread your protein out over 3-4 meals to maximize how much your body actually uses for muscle growth/recovery.

• Eating too much protein if you aren’t moving around, or if you are dehydrated, can be stressful on your body. Context matters!

Shoenfeld, BJ and A Aragon, (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. J International Society of Sports Nutrition.

Reitman, A et al., (2014). High dietary protein intake, reducing or eliciting insulin resistance? European J Clinical Nutrition.