Nutrition researchers declared more than thirty years ago that plant foods can provide adequate protein. But “where do you get your protein?” is a question that most vegans have heard more times than they can count. Many of the questions about protein in plant-based diets stem from confusion over what it means for proteins to be “complete.”
Proteins are made of chains of twenty different amino acids. Some amino acids can be made by the body (generally from other amino acids) and therefore we don’t need a dietary source of them. Others— the essential amino acids (EAAs)—must be supplied by the diet.
Proteins in the human body tend to have a consistent ratio of EAAs. Because the percentage of EAAs in animal products and soybeans are a close match to those in the human body, proteins from these foods are considered “complete.” Plant foods like grains, beans and nuts have a lower percentage of at least one essential amino acid, making them “incomplete.” For example, beans (other than soybeans) are low in the EAA methionine, and grains are low in lysine. But when grains and beans are consumed together, their amino acid profiles complement each other and produce a mix that is “complete” and therefore a good match to the body’s needs.
Complete And Incomplete Proteins
In the early 1970s, the idea that vegetarian meals should contain these specific complementary pairings was popularized in Diet for a Small Planet by Frances Moore Lappe. Today we know that the theory about what happens when protein foods are combined in this way wasn’t wrong; it just turned out to be unnecessary. Newer research has shown that the body maintains its own storage supply of the essential amino acids. We need to keep replenishing that storage with all of the amino acids, and so it’s important to eat a variety of plant foods. But the old idea that certain combinations of plant foods—the complementary pairings—must be consumed together isn’t true.
While fruit is extremely low in protein, and oils don’t provide any, all other plant foods contain protein. One common misconception is that plant foods are completely without one or more amino acids. That’s not true. All plant sources of protein contain at least some of every essential amino acid. In fact, you could get enough protein and all of the essential amino acids by eating just one type of food like pinto beans. You’d need to eat a lot of them, though—about four cups per day. That’s not practical, partly because it would be boring, but also because all those beans are likely to displace foods that are needed to satisfy other nutrient requirements. So eating a variety of protein sources makes better nutritional sense.
Protein RDA For Vegans
Protein needs are calculated on the basis of healthy (or “ideal”) body weight—that is, what a person with a healthy amount of body fat weighs. Scientists use the metric system, so U.S. protein needs are determined using your healthy weight in kilograms.
The protein RDA for adults is 0.8 grams of protein per kilogram of ideal body weight, but along with most other vegan dietitians, we recommend a slightly higher protein intake for vegans. This is because plant proteins are not digested as well as animal proteins. Since both cooking and processing often improve protein digestibility, this may be less of an issue for vegans who consume more foods like tofu or veggie meats made from processed soy protein. For those who are depending on whole foods like legumes, nuts, and grains for most of their protein, the digestibility factor comes into play.
It’s not a big difference, but vegans should strive for a protein intake of 0.9 grams per kilogram of body weight. For ease of calculation, this translates to around 0.4 grams of protein per pound of healthy body weight. So a vegan whose healthy weight is 150 pounds would need 60 grams of protein (150 x 0.4) per day.
Since protein needs vary considerably among individuals, the RDA is designed to cover the needs of 97 percent of the population and is therefore more than what many people need. Without any way of knowing where you fall on the protein-need spectrum, and because recent research suggests that protein recommendations could be too low,5 it’s a good idea to play it safe and aim for the RDA.
For children and teens, we would use an RDA aimed at the needs of different age groups and calculated specifically for vegans.
Meeting Protein Needs On A Vegan Diet: The Importance Of Legumes
While the chart on page 19 shows that many plant foods are good protein sources, legumes are especially rich in protein. Legumes include beans, peas, lentils, soyfoods (like tofu, soymilk, and veggie meats), and peanuts. (Most people think of peanuts as nuts, but they are botani-cally legumes and, from a nutritional standpoint, they have more in common with pinto beans and lentils than walnuts and pecans.) Our food guide specifies at least three to four servings per day of these foods. A serving is pretty modest: V cup of cooked beans, V cup of tofu or tempeh, a one-ounce veggie burger, one cup of soymilk, or two tablespoons of peanut butter. Planning menus that include these foods isn’t difficult, and we give you several tips for doing so in other articles.
In addition to being protein-rich, these foods are the only good plant sources—with a few exceptions—of the essential amino acid lysine. A diet that gets most of its protein from grains, nuts, and vegetables is likely to be too low in lysine. And while some popular resources suggest that very low protein intakes—as little as 5 to 6 percent of total calories—can meet our nutritional needs, it’s actually difficult to get enough lysine (or total protein) on a diet that isn’t more protein-dense.
You can get a rough idea of how much lysine you need by multiplying your weight (in pounds) by 19. This calculation includes a small factor that makes up for the slightly lower digestibility of protein from whole plant foods. For example, a person weighing 140 pounds would need 2,660 milligrams of lysine per day. The chart on page 21 shows that the best sources of lysine are legumes, quinoa, pistachios, and cashews.
If you follow our recommendations to consume at least three to four servings of legumes per day, you’ll meet lysine needs with ease. That doesn’t mean that beans, peanuts, and soyfoods are absolutely essential in vegan diets. While it is difficult to meet protein and lysine needs without them, it’s possible.
Vegan Protein: Meals That Deliver
It’s easy to build meals that pack a substantial protein punch. Each of these meals provides at least 20 grams of protein.
Easy Oatmeal Breakfast
► 1 cup of oatmeal with V cup soymilk
► 1 slice whole-wheat bread with 2 tablespoons almond butter
■ Total protein: 20.5 grams
Indonesian Tempeh With Peanut Sauce
► 1 cup of rice
► V cup tempeh
► VV cup sesame tahini sauce
► 1V cups steamed broccoli
■ Total protein: 35 grams
Bean And Beef Taco Dinner
► 2 taco shells
► V cup refried beans
► V cup veggie “ground beef” cooked in tomato sauce
► Chopped tomatoes and lettuce
► 1 cup steamed spinach
■ Total protein: 20 grams
► 1 cup pasta
► V cup garbanzo beans
► 2 tablespoons pine nuts
► 1 cup chopped broccoli
► V cup roasted red pepper strips
■ Total protein: 23 grams
Lunch On The Go
► Instant lentil soup with 2 tablespoons pumpkin seeds
► 1 slice whole-wheat bread with mashed avocado
■ Total protein: 21 grams
Overt protein deficiency is rare among Americans and occurs in other parts of the world where people don’t have enough food. Many vegan advocates point out that people don’t end up in hospitals because of a protein deficiency. It’s true that in countries where food is abundant, acute deficiency of protein doesn’t occur. But diets that are marginal in protein—not quite deficient, but not quite optimal—can result in loss of muscle mass, poor bone health, and compromised immunity. And those kinds of problems do occur in the United States.
We’d like to say that vegans never need to worry about protein, but that isn’t entirely true. There are a few situations where vegans may fall short on meeting their protein needs.
Vegan diets that are low in protein-rich foods like legumes are likely to be too low in protein. And because low-calorie diets raise protein requirements, people who are dieting or simply not eating enough for other reasons (like chronic illness) may need to boost their intake of protein-rich foods like legumes or soyfoods.
Obviously, junk-food vegan diets—those based on potato chips, French fries, and soft drinks—can be too low in protein (and too low in just about everything else that you need to be healthy).
And extreme versions of vegan diets, such as raw foods or fruitarian regimens, are often low (or completely lacking) in the higher-protein plant foods like legumes and soyfoods and can lead to a marginal protein intake. That’s one reason these types of diets are not recommended for children.
Do Vegans Get Adequate Tryptophan?
One common belief, often voiced by critics of vegan diets, is that plant foods don’t provide adequate tryptophan. This essential amino acid is needed to make the neurotransmitter serotonin, and low levels of serotonin are linked to depression. Meat is higher in tryptophan than plants, but a well-balanced vegan diet is almost guaranteed to provide more than enough of this amino acid. The FNB recommends 5 milligrams of tryptophan for every kilogram of healthy body weight. Adding in a factor for plant protein digestion, this translates to a vegan RDA of 5.5 milligrams per kilogram of body weight or 2.5 milligrams of tryptophan per pound.
For example, a vegan who weighs 130 pounds would need 325 milligrams of tryptophan, which is easily provided on a vegan diet. A diet that includes one cup of black beans, V cup of tofu and one cup of brown rice would provide nearly 400 milligrams of tryptophan.
In fact, eating foods that are very high in protein, like meat, doesn’t necessarily increase the amount of tryptophan in the brain. That’s because high levels of other amino acids in these foods block absorption of tryptophan from the blood into the brain. Eating foods like legumes that provide both protein and carbohydrates can actually enhance the passage of tryptophan into the brain.
Tips For Meeting Vegan Protein Needs
- Consume adequate calories to maintain a healthful weight. If your calorie intake is low because you are dieting or for any other reason, you may need to add a few additional protein-rich foods to your menus.
- Eat a variety of plant foods every day.
- Aim for at least three to four servings of legumes in your daily menu. A serving is 1/2 cup cooked beans, 1/2cup tofu or tempeh, 1/4 cup peanuts, one cup soymilk, or 2 tablespoons peanut butter.
- If beans give you discomfort from gas production, choose more lentils and split peas (they’re less gassy) and include some veggie meats, tofu, or tempeh in your menus.
- If you include plant milks in your diet, choose soymilk at least some of the time. Milks made from almonds, hempseed, and rice are low in protein.