On nutrition: Questions about incomplete proteins

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Reader Ann F. writes, “I remember learning a little about incomplete protein a long time ago, and that if you combined, say, beans with corn, you had a complete protein, kind of like you had eaten eggs or meat or cottage cheese, I always thought they should be eaten at the same meal.

“But I wonder, suppose you have an incomplete one for breakfast and the other for lunch – or for dinner – or maybe even the next day? I looked online, but I don’t learned nothing about timing.”

“So I would be interested in your views on that, and also on quantities – should the portions be of equal size, or, for example, should a spoonful of corn with a large serving of beans , or vice versa, would work just fine?”

“And I wonder if some combinations are better than others. A peanut butter sandwich (whole wheat bread), for example, is it better or worse than beans and corn? Or is it just a good idea to eat a wide variety of foods?”

Great questions, Ann, because advice on this has changed over the years. According to the most recent position paper on vegetarian diets from the Academy of Nutrition and Dietetics (eatright.org), protein from a variety of plant foods eaten throughout the day provides enough essential amino acids to meet your protein needs. (Amino acids are needed to “build” over 100,000 different proteins in the human body.)

Experts say the best balance of plant protein comes from eating grain foods (which are limited in lysine, an essential amino acid, but contain a good amount of methionine and cysteine) as well as legumes (which contain enough of lysine, but are lower in methionine and cysteine).

So a diet that includes grains such as wheat, oats, rice, and corn (corn is considered a grain as well as a vegetable) in addition to legumes like beans and peas can provide all the building blocks your body needs to make complete proteins.

Soy is also a legume, and here is its claim to fame: because it contains all the essential amino acids we need, it is considered a complete vegetable protein.

To use your examples, then, corn and beans in normal portions would fill each other’s protein “gaps”, whether you were then eating at the same time…or not. Similarly, peanut butter (peanuts are legumes) and bread (cereals) are also complementary.

And yes, the more varied foods you eat on a vegetarian diet, the better, experts say. Besides legumes and grain combinations such as bean burritos or lentils and rice, remember that most vegetables also contain small amounts of protein to contribute.

Choose these foods throughout the day to ensure your body is getting all the ingredients it needs to keep you strong!


Quinn on Nutrition: Incomplete Protein


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