I’m a vegetarian – do I need to combine proteins in one meal?

The question: I'm a vegetarian. I've heard I need to combine certain proteins in the same meal. Is this true?

The answer: No, this isn't true. The notion of protein combining – eating certain plant foods together in the same meal (e.g. grains with beans) – was introduced in the 1970s as a way to consume the perfect mix of amino acids at each meal. (Amino acids are the building blocks of protein.) Protein-rich foods supply your body with 20 amino acids, all of which are needed for good health. Eleven of these can be manufactured by your body and are called non-essential amino acids. The remaining nine, however, must come from your diet because your body cannot synthesize them on its own. They're called, as you may have guessed, essential amino acids.

Animal and plant proteins have different amino acid profiles. Animal protein foods contain all nine essential amino acids in sufficient quantities to support growth and repair and maintenance of body tissues. That's why you might have heard animal proteins such as meat, dairy and eggs referred to as "complete" proteins. Plant proteins, on the other hand, are low in one or more essential amino acids. The proteins from plant foods are considered "incomplete" proteins for this reason.

It was once thought that strict vegetarians needed to combine a plant food low in one essential amino acid with another containing large amounts. For example, legumes, which are low in an amino acid called methionine, could be eaten with nuts or seeds, which are a good source of methionine. Beans could be combined with grains to provide the amino acids missing from them. By combining foods in this way vegetarians would be able to consume all nine essential amino acids.

If this sounds complicated, that's because it is! The good news is that today we know it isn't necessary to combine proteins at meals. As long as you eat a variety of plant foods throughout the day, your body will get all the amino acids it needs. If you eat only a few foods and your diet lacks variety, however, you probably won't get enough essential amino acids.

Send dietitian Leslie Beck your questions at dietitian@globeandmail.com. He will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail website. Your name will not be published if your question is chosen.

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