In my early-70s Cambridge commune, dinner table debates frequently and endlessly focused on what exactly you needed to eat to get enough protein – in our case, from a vegetarian menu. We read “Diet for a Small Planet,” bandied about terms like “complete protein” and “complementarity,” and usually came to the same conclusion: beans must be eaten with rice; curried veggies need yogurt, etc. So years later when I heard a tomato being touted for its good protein, I guffawed; next came egg whites! Could these be true protein?
Proteins are called “the building blocks of life.” Well-run bodies rely on 20 amino acids, 13 of which our bodies produce. The remaining nine “essential amino acids” we get when we digest protein — which involves breaking it down into its component amino acids and then reassembling them to create hormones, enzymes, neurotransmitters, etc.
One amino acid that we must get from food is tryptophan, featured in a recent Washington Post article, “The Turkey is not to Blame…” Tryptophan is used to produce the brain chemical serotonin, which makes you feel relaxed and sleepy. When consumed in a complete protein like turkey, however, other amino acids compete for the same transporter proteins that carry them to your brain, with the result that eating complete protein actually blunts the production of serotonin. Thanksgiving Day side dishes and desserts, like sweet potatoes and pecan pie, on the other hand, are rich in carbohydrates, which “clear the path for [serotonin] to get to the brain fast,” according to the Post article, which quotes Judith Wurtman, author of “The Serotonin Power Diet:” “Carbohydrates soothe and tranquilize.”
The label “complete protein” can be applied only to foods that contain all nine amino acids: meat, poultry, fish, dairy products and eggs, with a few other controversial possibilities including quinoa, hempseed, buckwheat, soy. Foods that are “incomplete proteins” – most nuts, seeds, vegetables, grains – are missing or low in one or more amino acids, and thus must be combined with other foods to meet the body’s needs. Combinations such as red beans and rice, or spinach salad with sesame seed and almond dressing provide high amounts of all the essential amino acids. These combinations do not need not be consumed together or at the same meal as long as all nine bases are covered throughout the day.
Another variable in evaluating foods for protein content is the PDCAAS (protein digestibility corrected amino acid score), which measures the “quality” or absorbability of proteins. Because animal protein, including meat and dairy, is more easily absorbed than that in buckwheat, for example, and in incomplete-protein foods like beans, you need to eat less of it to get the desired amino acid combination.
As for how much protein you should eat, the Recommended Daily Allowance for adults is .36 grams/pound of body weight, or about 45-50 grams/day for a 136-pound woman. Alternatively, a 1,600/day-calorie diet should include 10-35 percent protein or 40-140 grams of protein.
In general, though, such parameters should not be considered too rigorously. “Eating for complete protein isn’t a scientific system of food combining [but] a natural traditional way of eating,” according to Dr. Linda Posch in the Savvy Vegetarian.
As for tomatoes and egg whites, one tomato contains one gram of protein, which, while not providing complete protein, is considered to make an important contribution to a “complete protein day.” In the same way, an avocado contributes three grams of protein; and a potato with skin, four grams. Egg whites, along with the whey in milk, are themselves complete proteins.