Ask a Nutritionist: Are Plant Proteins Complete?

Many sources claim that certain plant proteins need to be combined very specifically at every meal in order for the human body to utilize them as well as animal proteins. This theory is not exactly true.

All proteins are made up of different amino acids, some of which are essential — meaning the body cannot manufacture them on its own and they need to come from food sources. Different protein sources have varying amounts of each of the amino acids. For example, wheat proteins are typically lower in an amino acid called lysine and higher in the amino acid methionine. Beans are the opposite; they are a bit lower in methionine and higher in lysine. It stands to reason that eating the two in combination will then result in a “complete protein” that the body can effectively utilize.

While this is true in theory, the good news is that these “complementary” proteins do not need to be eaten in the same meal. Recent research has actually shown that an assortment of plant foods eaten throughout the day can provide a more than adequate quantity of protein. These foods will provide all of the amino acids in adequate quantities without having to carefully plan the consumption of complementary proteins at every meal. This is because our bodies contain an amino acid pool that acts as short-term storage for these different amino acids that can be drawn upon as necessary. Meaning, amino acids consumed earlier in the day will eventually be combined with those eaten later in the day to a proper amount of protein.

A recent meta-analysis found no significant difference in protein needs due to a protein source, whether it be plant- or animal-based, suggesting plant proteins are utilized just as effectively as animal proteins. In other words, a varied and appropriately planned vegetarian or vegan diet is nutritionally sufficient when it comes to protein. In fact, almost all Americans, including vegetarians and vegans, consume more protein than is actually needed.

This post was originally written by Colleen McConnell, MS Candidate in Nutrition at NYU and James J Peters VA Medical Center Dietetic Intern, and published by the Natural Gourmet Institute. Learn more about today's Natural Gourmet Center.

References:
Completing The Limiting Essential Amino Acid Picture (2013)
Position of the American Dietetic Association: Vegetarian Diets (2009)
Plant proteins in relation to human protein and amino acid nutrition (Young 1994)
Protein Requirements in Healthy Adults: A Meta-analysis of Nitrogen Balance Studies (2014)