A Look at the Role of Protein and New Recommended Intakes
There seems to be a lot of buzz around consuming protein. Those advocating for increasing muscle mass are huge enthusiasts of increasing protein and I see protein EVERYTHING when I scroll through instagram. But protein isn’t praised just by those interested in growing muscle mass, there seems to be a growing consensus that increasing protein intakes is helpful for overall health.
I thought it would be helpful to dive into what the science says regarding protein intake and what actual literature suggests rather than just taking people’s word for it (even people I highly respect).
Protein and its role in the body
So what is protein and what is it used for? Proteins are molecules made up of individual amino acids in varying configurations (depending on the protein). There are roughly 500 amino acids found in nature, but our bodies only use 20 of them. The 20 amino acids used by our body can be divided into two categories—essential and non-essential. The eleven non-essential amino acids can be made in the body from other amino acids and therefore don’t have to be consumed in our diet. Our bodies lack the enzymes necessary to make the other nine essential amino acids so they MUST be consumed through the diet (hence the term “essential”). The amounts of these essential amino acids in our diet and in our body are the limiting factor for protein synthesis (if our body needs to make a protein requiring one of these essential amino acids and it doesn’t have it, our body simply won’t be able to make the protein needed). In general, animal sources of protein are complete proteins, meaning they have all 9 essential amino acids, along with non-essential amino acids. There are a few plant sources of complete proteins (soy, quinoa, chia seed, etc), but for the most part, plant sources of protein will contain only some of the essential amino acids. This is why it is important to use multiple plant protein sources so that they can complement one another and provide the missing essential amino acids (such as combining beans with legumes).
Protein is used for MANY processes in the body. Lean muscle mass is probably the most recognized use for protein since muscle mass is made up of proteins. But protein plays a role in our immune system, gene expression, and hormones; and makes up cellular structures, hair, skin, and enzymes, which carry out every chemical reaction in our cells. Protein is a pretty big deal! If our intake of protein is inadequate to our needs, or is lacking in essential amino acids, our body’s processes will be halted. I also want to note the importance of eating enough overall calories. If we are not consuming enough energy, our bodies will utilize protein as a source of energy rather than using it as building blocks for the necessary structures/enzymes/hormones. We also know that protein takes longer to digest (compared to carbohydrates) and leads to increased fullness and satiety and can help with slowing down the digestion and absorption of carbohydrates, helping with blood sugar stabilization.
The role of protein in muscle growth
At all times, the body is tearing proteins down and building up new ones. We call this muscle protein breakdown and muscle protein synthesis. In order to build muscle mass (or “lean mass”), our net protein synthesis has to be greater than our protein breakdown. The ONLY way to have protein synthesis greater than breakdown is to supply adequate dietary protein. You can’t build something if you don’t have the necessary building materials. Strength training significantly stimulates muscle protein synthesis AND increases sensitivity to amino acid uptake, which is why fueling after a workout is so important (utilize that increased synthesis!)
You can see why those promoting building muscle mass also promote eating large amounts of protein. But here’s the deal, there’s a limit to how much your body can utilize and incorporate into muscle synthesis. A study by Stokes et al. suggests that muscle protein synthesis is a saturable process and that there is no benefit to having a higher intake of amino acids than the muscles can use.(1) The authors reported that muscle synthesis was negligibly increased above 20 g protein after a workout, with no difference at 40 g protein (compared to 20 g). Our bodies only use about 10% of the amino acids consumed after a workout (2.2 g of 20 g protein bolus in this case), meaning that it is important to be consuming protein regularly throughout the day in order to build muscle mass. Eating one large meal of protein after a workout won’t be as effective as eating more moderate protein meals/snacks throughout the day since the remainder of the protein would be used for energy rather than muscle synthesis or body protein needs. It’s also important to note that the body sends amino acids to the muscles AFTER the gut cells and liver have used what they need. If you are not consuming enough protein regularly throughout the day, the gut and liver are preferentially going to use the amino acids rather than sending them to your muscles.
So how much should we be consuming? New recommendations
When I was in school, I was taught that the average person needs 0.8 g/kg/day (0.36g/lb/day) in order to meet body protein needs. This was determined using the nitrogen balance method. New advances in technology suggest that the indicator amino acid oxidation (IAAO) method may be a more accurate test for determining protein needs. It takes into account essential amino acids being a limiting factor to amino acid utilization in the body (remember, if your body lacks the essential amino acid it needs for building, it won’t build that protein and instead will just use the amino acids for energy production). This new IAAO method suggests that previous protein recommendations were far too low. (2)
I found multiple studies suggesting new increased protein recommendations based on the IAAO method. They ranged from 0.91-0.99 (0.41g-0.45 g/lb/day) to 1.5-2.2g/kg/day (0.68-1g/lb/day) for general health and wellbeing (2,3,4). Additionally, the study by Stokes et. al recommends intakes for those wanting to build muscle mass to be 0.73-1 g/lb/day. (1) I know that's a lot of numbers!! 🤪 Just know that we need more protein than previously thought. I have seen a lot of recommendations online for calculating protein needs starting at 1 g/lb (gram per pound) and going beyond. And although the recommendations are higher than before, I found no literature that supported benefit over 1 g/lb (except for in extremely low calorie diet trials, which I don’t support and isn’t relevant to this article). The previous recommendations were 0.7 g -1.2 (even all the way to 1.5) grams of protein per kilogram and I’m curious if people saw those recommendations and thought they were per pound. Hence the common recommendations of over 1 gram of protein per pound. Just speculation!
In the past, I believed that too much protein was hard on the kidneys , but it seems there is now no evidence to support that claim in the general, healthy population (I’m constantly have to learn new information too!)(4). So eating above that 1 g/lb isn’t likely to cause any harm, but I would argue that eating more than that (or more than 35% total calories from protein) would be at the expense of eating other necessary food groups. Is it really beneficial/helpful to be stuffing protein, but then be too full to consume adequate fruits, vegetables, and other plants? Additionally, consuming that much protein can be difficult and unenjoyable/unappetizing. I’m a firm believer that a healthy way of eating and interacting with food is one that is full of enjoyment and satisfaction. Eating at the higher end of the recommendations and above may simply be unsustainable or set you up for bingeing because of feeling unsatisfied. So yes, maybe try increasing your protein intake or increasing awareness of how much you’re taking in, but not at the expense of your relationship with food. ☺️
So as a recap:
Dietary protein is important for stabilizing blood sugar, providing satiety, providing the building blocks for many structures/processes in our body, and building muscle mass.
Protein synthesis in the body is limited by the essential amino acids. It is important to be consuming adequate complete proteins or a combination of incomplete proteins to ensure the body can use amino acids for protein synthesis instead of energy production.
For general health, aim anywhere from 0.45-1g/lb/day. (150 pound individual would aim for 59-150 grams of protein/day). I’d aim for the middle range if increasing muscle mass isn’t your goal.
If you’re wanting to build muscle mass, aim for 0.73-1g/lb/day (150 pound individual would aim for 110-150 grams of protein/day)
There isn’t evidence to suggest that eating too much protein is harmful for the kidneys for the general population, but it could be at the expense of other important food groups/nutrients (like fiber or phytonutrients)
Keep in mind enjoyment and satisfaction. .
If you are needing help learning how to incorporate more protein rich foods into your diet or wanting to increase muscle mass, but are having difficulty, reach out and we can talk about working together to accomplish your goals.
I’d love to hear any thoughts you have in the comments!
References:
1 Stokes T, Hector AJ, Morton RW, McGlory C, Phillips SM. Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients. 2018;10(2):180. Published 2018 Feb 7. doi:10.3390/nu10020180.
2 Elango, R., Ball, R. O., & Pencharz, P. B. (2012). Recent advances in determining protein and amino acid requirements in humans. British Journal of Nutrition, 108(S2). https://doi.org/10.1017/s0007114512002504
3 Paul B. Pencharz, Rajavel Elango, and Robert R. Wolfe. Recent developments in understanding protein needs – How much and what kind should we eat?. Applied Physiology, Nutrition, and Metabolism. 41(5): 577-580. https://doi.org/10.1139/apnm-2015-0549
4 Stuart M. Phillips, Stéphanie Chevalier, and Heather J. Leidy. Protein “requirements” beyond the RDA: implications for optimizing health. Applied Physiology, Nutrition, and Metabolism. 41(5): 565-572. https://doi.org/10.1139/apnm-2015-0550