I was hoping you could explain about the proteins in beans and legumes. I've heard some vegetarian friends say you have to have a grain with your beans to make a complete protein out of the nutrients. It just doesn't jive. If the nutritional content is 9g protein per serving, isn't that what's there? Thanks!
Great question! And here's the answer, from Sally Fallon Morell in Nourishing Traditions:
“Proteins are the building blocks of the animal kingdom. The human body assembles and utilizes about 50,000 different proteins to form organs, nerves, muscles, and flesh. Enzymes — the mangers and catalysts of all our biochemical processes — are specialized proteins. So are antibodies.
All proteins are combinations of just 22 amino acids, eight of which are “essential” nutrients for humans, meaning that the human body cannot make them. When the essential amino acids are present in the diet, the body can usually build the other “nonessential” amino acids; but if just one essential amino acid is low or missing, the body is unable to synthesize the other proteins it needs, even when overall protein intake is high.
Just as animal fats are our only sources of vitamins A and D and other bodybuilding factors, so also animal protein is our only source of complete protein. All of the essential amino acids, and many considered “nonessential,” are present in animal products. Sources of protein from the vegetable kingdom contain only incomplete protein; that is they are low in one or more essential amino acids, even when overall protein content is high. The body must ingest all the essential amino acids in order to use any of them.
The two best sources of protein in the vegetable kingdom are legumes and cereal grains, but all plant foods are low in tryptophan, cystine and threonine [2 essential and 1 non-essential]. Legumes, such as beans, peanuts and cashews are high in the amino acid lysine [essential] but low in methionine [essential]. Cereal grains have the opposite profile.
In order to obtain the best possible protein combination from vegetable sources, pulses and grains should be eaten together and combined with at least a small amount of animal protein. Most grain-based cuisines instinctively incorporate this principle. For example, animal products plus corn and beans are staple fare in Mexican cuisines, as are chickpeas and whole wheat in Middle East and rice and soybean products in Asia.”
So, there you have it. Grains and beans don't contain all the essential amino acids alone. But combined they can, although some combinations might still be low in certain essential amino acids – making a small amount of animal protein eaten alongside such a meal a tremendous benefit. Also, as Sally Fallon Morell points out here and elsewhere, grains and beans lack essential fat-soluble vitamins, such as A & D, and protein should always be eaten with fat for best assimilation.
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