I’ve talked with three different reporters this past month, all with questions about vegetarian diets. All three asked, of course, which nutrients require special attention in vegetarian diets. And each expressed surprise that I didn’t mention protein. They also asked about soy—and whether it was true that it’s the only plant food that is a “complete protein”—ie, the only one that contains all 9 of the essential amino acids.
The answer is no. All plant foods that contain protein—which would be all grains, beans, nuts, seeds and vegetables—provide all 9 of the essential amino acids. So they are all “complete proteins.”
It’s true, though, that certain plant proteins are lower in quality. They are still “complete,” but some of their amino acids are a little on the low side. You would need to eat more of these foods to meet amino acid needs if they were the sole source of protein in your diet. In fact, you would have to exceed the total requirement for protein in order to meet needs for each of the essential amino acids.
So it’s true that if you wanted to meet protein needs from one plant food alone, soy protein would be your best bet. But it’s kind of irrelevant because if you ate only one source of protein, your diet would be deficient in other nutrients. Not to mention the fact that it would be impossibly boring. So people—whether they eat animal foods or not, get protein from a variety of foods. And when vegans consume a variety of protein sources—bread, rice, pasta, veggies, peanut butter, tofu, baked beans, etc—these foods work together to provide the full complement of essential amino acids.
In fact, if you eat a variety of foods from all the vegan food groups and you get enough calories, it is virtually impossible to fall short on protein. So why worry about whether one plant food is more complete than another? There is no single food that you have to eat (including soy!) and you don’t need to eat careful combinations of foods at meals.
The only people who might need to take care to boost protein intake a little bit are those on very low calorie diets. If you are weight watching, you might want to include a few servings of higher-protein foods like tofu or tempeh in your daily diet to make sure you are meeting protein needs.
Otherwise, eat a good variety of whole foods—and don’t worry about protein!