Author: Maria Fischer • Fact checked by: Tara D. Thies • Oct. 20, 2020
We all know that getting an adequate amount of protein is necessary for staying in shape and achieving fitness goals like building muscle mass and losing weight — but why? How exactly does protein help you build and maintain muscle?
Protein plays an important role in the creation and maintenance of every cell in our bodies. When you eat protein, your body breaks the protein down into amino acids. Those amino acids, often referred to as the building blocks of protein, are then used to repair and grow new muscle fibers.
Amino acids are categorized as essential amino acids, conditionally essential amino acids or non-essential amino acids. Their classification depends primarily on to what degree the body is able to synthesize them. A non-essential amino acid is an amino acid that our bodies can produce, even if we do not get it from the food we eat. An example of a non-essential amino acid is alanine. The amino acids that cannot be made by the body are essential acids. As a result, essential acids must come from food.
(Conditionally essential amino acids are amino acids that only become essential in certain situations depending on a person’s metabolic state. For example, amino acids like arginine and histidine may be considered conditionally essential because the body cannot synthesize them in sufficient quantities during certain physiological periods of growth, such as pregnancy or adolescent growth.)
There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. They all play different, but equally important, roles in maintaining the body’s vital processes. Some amino acids, such as histidine, phenylalanine and tryptophan, produce neurotransmitters that regulate immune response, appetite, digestion, mood, sexual function and sleep-wake cycles. Others, like threonine, lysine and methionine, are important for the skin’s collagen and elastin production and the body’s metabolism and detoxification.
But for promoting muscle growth, three amino acids — known collectively as branched-chain amino acids (BCAAS) — are key.
The three BCAAs are leucine, isoleucine and valine. These essential amino acids are used by the body to alleviate fatigue, improve athletic performance and stimulate muscle recovery after exercise. In fact, a recent review of eight studies determined that supplementing with BCAAs was even superior to rest in promoting muscle recovery and reducing soreness after intense exercise.
A 2017 study published in the peer-reviewed journal Applied Physiology, Nutrition, and Metabolism looked further into the effects of BCAA supplementation on recovery from exercise-induced muscle damage. For the study, researchers randomly assigned 16 experienced, resistance-trained athletes to a BCAA group or a placebo group. The BCAAs were administered at a dosage of 0.087 g/kg body mass, with a 2:1:1 ratio of leucine, isoleucine and valine. The participants performed six sets of 10 full-squats at 70% one-repetition maximum to induce muscle damage, and all participants were diet-controlled across the study. Perceived muscle soreness and countermovement jump height were measured pre-workout, as well as one hour, 24 hours and 48 hours post-workout. The study found that supplementation of BCAAs improved performance and increased the rate of recovery in perceived muscle soreness compared with the placebo.
The study mentioned above followed experienced athletes, but BCAAs have been shown to boost strength performance and muscle recovery in non-athletes as well. The results of a controlled clinical trial published in The International Journal of Sports Physiology and Performance show leucine supplementation can also enhance strength performance in untrained athletes. For a 12-week resistance training program, 13 initially-untrained male participants ingested 4 g/d of leucine, while 13 others in a placebo group ingested a corresponding amount of lactose. All participants trained under supervision twice per week, following a prescribed resistance training program using eight standard exercise machines. Testing took place at baseline and at the end of the supplementation period. At the end of the 12 weeks, the leucine group demonstrated significantly higher gains in total strength, suggesting essential amino acids like leucine help prevent fatigue, improve athletic performance and stimulate muscle recovery after exercise in all types of people, not just bodybuilders or athletes.
While it’s clear from numerous studies that BCAAs are important for strength building and muscle recovery, your muscles still benefit from a mix of amino acids — even the ones that aren’t BCAAs. Together, the nine essential amino acids help prevent muscle loss — especially in older adults. A 10-day study published in the Clinical Nutrition journal followed 22 older adults on bed rest showed that participants who received 15 grams of mixed essential amino acids maintained muscle protein synthesis, while the process decreased by 30% in the placebo group.
Making sure your diet includes all the essential amino acids is one way you can help build muscle, prevent muscle breakdown and preserve lean muscle mass.
When it comes to amino acids, all proteins are not equal. According to a 2018 study published in the journal Amino Acids titled “Protein content and amino acid composition of commercially available plant-based protein isolates,” whey protein has the highest essential amino acid content at 43%, followed by casein protein (34%) and egg protein (32%).
Whey is the by-product of cheese production. During cheesemaking, special enzymes are added to heated milk. These enzymes cause the casein in milk to change to a solid state and separate from a liquid substance. That liquid substance is the whey protein, which is washed and dried into a powdered form that you can consume as a supplement. Even though whey protein goes through several processes before it’s ready for consumption, its amino acid profile is preserved. Whey features the highest biological value of any protein, which means the essential amino acids are absorbed and used more efficiently by your body compared to other sources of protein.
But even other animal proteins like casein and egg tend to be more easily digested by our bodies than plant protein. Your body is more likely to actually get (and then properly use!) the essential amino acids it needs when you consume an animal protein over a plant protein.
Several studies have verified that the amino acid contents are lower in plant-based protein: One 2019 study published in the peer-reviewed journal, Nutrients, compared the anabolic properties of plant protein to the anabolic properties of animal protein in an effort to determine the ability of these proteins to help maintain skeletal muscle mass in healthy people (particularly, healthy older people). Researchers confirmed that plant-based proteins have less of an anabolic effect than animal proteins due to their lower digestibility. Because a lower proportion of the amino acids in plants actually end up getting digested, they aren’t absorbed and utilized for things like muscle-building as efficiently. That means a person’s essential amino acid requirement would not be met if a plant protein (such as pea protein, soy protein and brown rice protein) is the only protein source consumed.
However, that doesn’t mean someone who is lactose intolerant or dairy free can’t get the amino acids they need. If you can’t supplement with whey or other animal protein because you are vegan or have dietary restrictions, such as lactose intolerance, you can try a protein combination that includes pea protein. Pea protein is a favored choice among plant proteins because pea protein contains all nine essential amino acids. Of the nine essential amino acids, pea protein also happens to be particularly high in BCAAs. Pea protein also has high amounts of iron and arginine, which promotes healthy blood flow and heart health.
Despite containing all nine essential amino acids, pea protein is not officially a complete protein, because it’s an inadequate source of methionine and cysteine. A complete protein provides at least 25 mg/g of methionine and cysteine, and pea protein only delivers around 11 mg/g. If you choose to supplement with pea protein over an animal protein like whey, you’ll still need to make sure you get proper amounts of methionine and cysteine from another non-dairy protein source, such as brown rice protein.
You don’t need additional amino acid supplements if you’re consuming the proper amount of protein. The protein in your diet will give all the BCAAs required — especially if you’re already supplementing with protein powder. Most people aim for the general target of nine grams of BCAAs per day for women and 12 grams per day for men. If you’re especially active, your body could require as much as 20 grams of BCAAs to maximize the benefits, but chances are, you’re getting all the BCAAs you need from a healthy diet and protein supplementation.
And if you’re worried about the opposite problem (getting too much BCAAS), rest assured: It’s pretty tough to take too much without really trying. A 2012 study published in the American Journal of Clinical Nutrition estimated that the upper limit of consumption for leucine, one of the three BCAAs, is about 35 grams per day (and that’s a conservative estimate, per the researchers). Since most BCAA supplements and BCAA powder are only partly made up of leucine, that means you’d have to consume more than 35 grams of BCAAs to reach the limit — an amount that most people are unlikely to reach, especially accidentally.
But if you’re still looking to get even more out of your protein, glutamine and protein supplementation are safe to take together (especially considering glutamine is one of the building blocks of protein).
Now you know all about EAAs, BCAAs... so how do you find the right protein for you to make sure your body is actually getting them?
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