The front page of The Daily Targum from Nov. 20 hailed the availability of JUST Egg, an egg substitute made from mung beans, in the dining halls.
As the world is realizing the advantages of plant-derived foods, it is important to remember that JUST Egg is still just mung beans. Most vegans and vegetarians are aware that all dietary proteins are not equal. While JUST Egg contains the same amount of protein as a conventional hen’s egg, it does not have the same protein quality.
Proteins are made of 20 individual amino acids of which at least nine are considered essential (or non-dispensable) in our diets. It is also important that we eat foods that contain these essential amino acids and also to consume them in appropriate ratios to each other. This is the definition of protein quality.
Animal proteins such as eggs, meats, milk, etc. are considered good sources both of protein quantity and quality since they usually contain a near-perfect balance of the essential amino acids. Very few plant proteins can match this. Exceptions are soy beans, a limited number of other legumes and a few seeds such as quinoa.
Mung beans, though, are notoriously deficient in the sulfur containing amino acids, methionine and cysteine. This means that consuming JUST Egg in place of a conventional egg could potentially lead to deficiencies of these essential amino acids. Luckily this problem can be easily avoided by the simultaneous consumption of a different food with abundant sulfur amino acids such as grains and seeds.
In vegetarian societies where a mixture of complementary foods is always consumed, witness the ubiquitous rice and beans. Beans are low in sulfur amino acids but have sufficient lysine. Rice (and other grains) has sufficient sulfur amino acids but are deficient in lysine.
I contacted JUST Egg and asked about the protein quality of its product. Unfortunately, its response did not provide any direct indication of protein quality although it did state that, at this time, it is not supplementing the product with additional amino acids.
So while we should welcome the availability of JUST Egg and other plant-based foods, it is important to remember that they still reflect the plants that they were made from. To obtain the best nutrition from such products, always consume them with the appropriate complementary protein source.
As an endnote, the Impossible Burger, which contains considerable soy protein, claims to have a protein quality equal to that of beef!
Dr. Malcolm Watford is a professor in the Department of Nutritional Sciences.