You can get all the protein your body needs by eating plants if you want to avoid protein from animal sources (Scientific Reports, Aug 8, 2019;9(10345)). Researchers used sophisticated blood tests and muscle biopsies to show that healthy young males were able to grow the same amount of muscle after eating 30 grams of a blend combining wheat, corn, and pea protein as they did after eating the same amount of milk protein (The Journal of Nutrition, Dec 2022;152(12):2734–2743). Many other studies found the same results; as long as you eat a wide variety of different plants, you don’t need to eat protein from animals (Med Sci Sports Exerc, Sept 1, 2022;54(9):1572-1581; Sports Med, Sept 2021;51(Suppl 1):59-74).
The “Essential Amino Acids”
When you eat any source of protein, you do not absorb whole proteins; you absorb the single building blocks of protein called amino acids, and chains of amino acids. Roughly 500 amino acids have been identified in nature, but only 20 amino acids make up the proteins found in the human body. Of these 20 amino acids, you need to eat only nine (the “essential amino acids”), since your body can make the other 11 amino acids from the essential nine. Some people believe that protein from meat is better at building muscles than plant protein because meat contains all nine essential amino acids and individual plant foods usually contain fewer than all nine. However, we have overwhelming evidence that protein from plants builds muscles just as well as protein from animals. If you eat several different plant foods, you will easily get all nine of the essential amino acids and suffer no protein deficiency or slowdown in muscle growth. Researchers have demonstrated that compared to meat protein, plant-derived protein has lower levels of specific amino acids such as leucine, lysine, and/or methionine (Amino Acids, 2018;50(12):1685–95). However, this is irrelevant to building muscle as long as you eat a variety of different plants (Clin Nutr, 2013;32(3):412–9).
Combining different plant-derived proteins can provide all the amino acids you need to build large and strong muscles. For example, combining corn, hemp or brown rice protein (which have low lysine and high methionine content) with soy or pea protein (which have low methionine and high lysine content) will provide protein with adequate amounts of all amino acids necessary for muscle growth (Sports Med, 2021;51(S1):59–74). You don’t have to eat the different plants together at the same time. If you eat one amino acid food source in the morning and then eat another amino acid source in the evening, or even the next day, you will meet your needs for all nine essential amino acids.
A plant-based diet helps to prevent many diseases, so I recommend trying to get your protein from plants whenever possible. Good sources of protein from plants include:
• legumes (beans, peas, soybeans and soybean products such as tofu)
• whole grains (wheat, quinoa, rice, oats, wild rice, barley)
• nuts, peanuts and other seeds
However, plants do not contain vitamin B12 and lack of B12 can cause nerve damage and dementia. If you eat little or no animal products, get blood tests for vitamin B12 and take B12 pills if your level of B12 is below 300 pg/mL. Higher levels may be desirable; check with your doctor.