To understand the difference between complete and incomplete proteins, you first need to get to know amino acids. These are the molecular building blocks that combine to form every gram of protein you eat. When you eat protein-rich foods, your body breaks those proteins back down into amino acids, explains Marie Spano, RD, CSCS, the Atlanta-based lead author of Nutrition for Sport, Exercise, and Health. Your body then uses those amino acids to build muscle, repair tissues, support metabolism, and help along other processes in the body. Of the roughly 20 amino acids, 9 are essential, meaning the body can’t make them. They include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine, according to the National Institutes of Health (NIH). The only way to get these amino acids is through food. Foods that contain all of them, and in amounts similar to those required by the body, are called complete proteins or complete protein sources, Spano explains. Meanwhile, those that do not contain enough of one or more essential amino acids is incomplete. RELATED: 15 Best Sources of Lean Protein
Complete vs. Incomplete Protein Foods
According to Harvard Health Publishing, all animal-based foods, including meat, dairy, and eggs, contain complete protein. The majority of plant-based protein sources, such as whole grains, legumes, seeds and nuts, spinach, broccoli, and mushrooms, are incomplete. However, some plant-based foods, such as soy, quinoa, buckwheat, and algae, are complete. While it’s commonly believed that incomplete protein sources have zero of at least one of the nine essential amino acids, that’s not actually the case, explains Abbie Smith-Ryan, PhD, CSCS, director of the University of North Carolina in Chapel Hill’s Applied Physiology Laboratory. Many incomplete protein sources have some of every single essential amino acid, just not in levels high enough for that protein to accomplish everything you want, she says. Leucine, which is a main driver of muscle building, tends to be relatively low in most incomplete sources of protein, says Constance Brown-Riggs, RD, CDCES, who’s based in Massapequa Park, New York. RELATED: What to Eat Before and After You Exercise
How to Get All of the Amino Acids You Need
If you regularly consume meat or a lot of animal products, you’re getting enough of all of the essential amino acids you need. (Most Americans are, according to Harvard University.) The current recommended daily allowance for protein is 0.8 gram (g) per kilogram of body mass. However, many recent studies, including an article published in July 2015 in Applied Physiology, Nutrition, and Metabolism, suggest more, up to double that amount, is necessary for optimal muscle health, especially in older adults and those trying to lose weight or build muscle. But what if you don’t eat meats or animal products or are trying to cut down on how much of them you eat to focus on a more plant-based diet? After all, filling up on plant-based protein sources is associated with better overall health and longevity, according to an August 2016 study published in JAMA Internal Medicine. (Researchers explain this may be due to the fact that high-protein plants also tend to be brimming with fiber, vitamins, minerals, and antioxidants.) The good news: Experts all agree that by eating a wide variety of plant-based protein sources you can get all of the amino acids you need on a vegetarian or vegan diet. That said, how complicated this is is up for debate. RELATED: 9 Scientific Benefits of Following a Plant-Based Diet For example, a February 2017 study published in The American Journal of Clinical Nutrition found that there’s no significant differences in muscle mass or strength in the general population based on what foods people eat to get their protein. But other studies, including a March 2017 article in Nutrition in Clinical Practice, suggest that vegetarians and vegans, especially older ones, may need slightly more total daily protein compared with omnivores to enjoy the same protein benefits. This may be due to the body being able more easily to digest, absorb, and use incomplete proteins, according to the March 2017 article. Meanwhile, some experts say that to make incomplete proteins complete, you need to consume multiple and specific complementary proteins within the same meal. But as you can imagine, memorizing which plant-based foods have which essential amino acids and in what quantities — and then using that intel to craft every meal for the rest of your life — may not be realistic, Brown-Riggs says. “Will this make a difference in the end? It may depend on several factors,” Spano says. “I think the only true way to know is to do a crossover longitudinal trial with all meals provided. That’s one expensive study!” It’s likely that for adults eating a plant-based diet, getting protein from multiple sources throughout the day is sufficient, but it might not be ideal. “For someone who wants the most muscle and to maximally build structures in their body, I would try to combine proteins in each meal,” she says. Fortunately, whether you try to pair protein at each meal or do so throughout the day, you don’t have to worry about memorizing each amino acid. Just focus on variety, Smith-Ryan urges. Check off whole grains, legumes or protein-rich vegetables, and then a seed or nut, and you’ll be in a pretty good place with protein. RELATED: Why Are Healthy Eating Habits Important?
