Whenever I hear people talking about how nutritious a food is, I usually hear them talk about the amount and "quality" of the protein it contains. It's as if people really are getting sick from eating low-protein foods or foods with low-quality protein. They're not. In reality, it's practically impossible to avoid getting enough protein, including enough of all of the essential amino acids, as long as you are eating enough food to get enough calories.

To get a protein deficiency while getting enough calories, you'd have to eat nothing but a low-protein fruit (such as apples) or nothing but refined sugars and fats. If you eat enough of any sort of unrefined grains and vegetables, your protein requirements will be easily met.

What about the "quality" of the protein? People often talk about protein sources that are "high-quality" or "complete." They often warn that plant proteins are "incomplete." Although there are some important nutritional differences between plant proteins and animal proteins, you simply don't have to worry about the "completeness" of the protein in plant foods. The only "incomplete" protein that people are likely to find on their dinner plate is gelatin, which is extracted from animal bones.

Gelatin is incomplete because the caustic chemicals used in the extraction process break down some of the essential amino acids. You couldn't survive if gelatin were your only source of protein, but the proteins in plant foods are "complete" as far as human protein requirements go.

What is protein?

Proteins are huge molecules made up of smaller molecles called amino acids. The amino acids originally came from plants, which string them together to make their own proteins. When we digest a protein, we break it apart into individual amino acids again. Then our cells use the amino acids to make their own proteins.

Where protein comes from

Each of our genes is just a recipe that tells the cell which amino acids to use, and in what order, when making proteins. If there's a shortage of any of the amino acids, the cell can't make that protein. Although the recipes in our genes can call for up to 20 different amino acids, we need to get only 8 of them from our food. Our bodies can make the other ones, sometimes out of one of the other amino acids. Theoretically, if there's a shortage of any of the essential amino acids, it would be a limiting factor for an animal's growth.

How much protein do people need?

Scientists tended to follow one of three basic approaches to figuring out how much protein people need:

Each approach gives you a different answer, but only the third approach gives you a reliable answer.

People want more protein than they need

Carl von Voit was a 19th century German scientist who is considered to be the "father" of modern dietetics. From his clinical studies, Voit knew that men needed about 50 grams of protein per day. However, he based his recommendations for protein intake on the amount of meat that workingmen would like to eat, if they could afford as much as they wanted. So Voit came up with a recommendation of nearly 120 grams per day for men. Voit's recommendation was very popular, because it was based on what people wanted, not what was good for their health. When people eat as much meat as they want, they end up at risk for obesity, heart disease, and gout.

Why do people want to eat an unhealthy amount of protein? I think it's mainly because they like to eat an unhealthy amount of fat. When you analyze animal-based foods, you'll find that most of the calories come from fat. Fatty foods are a concentrated source of calories. Since starvation was the main dietary challenge that our species has always faced, it makes sense that we'd want to eat as much fatty food as we could get. Occasionally gorging on fat may have helped our ancestors survive long enough to reproduce, but continually gorging on fat is preventing a lot of people today from living long enough to get to know their grandchildren.

Rats need far more protein than people do

One of the main differences between people and rats is the rate of growth. People grow amazingly slowly, and rats grow unbelievably fast. If a woman and a rat conceive on the same day, the rat will probably give birth before the woman is even sure that she's pregnant. There are about 6 to 12 babies in a litter of rats, and the babies themselves can start breeding when they're about 65 days old. As long as the food supply holds out and there are no predators, the sheer weight of the rat population can grow explosively. It takes a lot of protein to produce all those pounds of rat bodies in so short a time.

You can stunt the growth of rats by feeding them plants instead of animal-based foods. That's because rats need so much protein. They also need a higher "quality" of protein than people need. Rats need to get adequate amounts of 10 different "essential" amino acids from the diet. The idea of combining different kinds of plant proteins to improve the "quality" of the protein came from studies of rats. These combinations are also important for other fast-growing animals, such as pigs and broiler chickens.

Although a high-protein diet and supplements of specific amino acids are useful for maximizing the growth of rats, pigs, and chickens, they are simply unnecessary for human beings. If you feed people any more protein than they really need, they just burn it for energy. So all those protein supplements are nothing but a dirty form of sugar. Ordinary unrefined starches and vegetables, such as rice or potatoes, provide all the protein that human beings need. We don't even need to combine different kinds of plant foods to get a "complete" protein. The only "incomplete" protein that human beings are likely to find on their plate is gelatin, which comes from animal bones.

It's practically impossible to get a protein deficiency

As long as you are eating any reasonable selection of unrefined plant foods, if you take care of the calories, the protein takes care of itself. The scientific evidence has been clear for over a century. In order to get a deficiency of protein, or any of the essential amino acids, you'd have to eat a bizarre diet. You'd have to eat nothing but apples, or nothing but extracted sugars and fats, or (as is much more likely) nothing but alcohol.

If you aren't getting enough calories, you will burn protein for energy. Protein supplements will do a starving person little good unless you give them enough calories that they stop having to burn up protein for energy. Since human beings grow so slowly, they can get by with a surprisingly low-protein diet. This fact is reflected in the relatively low protein content of human breast milk.

About 20 years ago, while I was editing the manuscript of a nutrition textbook, I learned that protein deficiency is a myth. As long as people get enough calories from any reasonable diet, they automatically get enough protein. The only people in the United States who were getting a protein deficiency despite eating enough calories were people who were getting nothing but glucose IVs, or babies who were being fed some bizarre substitute for breast milk, or alcoholics who were getting too many of their calories from booze. To see if that story had changed, I did a search on MEDLINE, which is an enormous database of medical and scientific journal articles. It includes just about any article of any importance and stretches back to the mid 1960s.

Sure enough, when I searched for "protein deficiency," I found that most of the articles dealt with pigs and chickens. When I limited the search to articles on human beings, I found that most of the "hits" were for articles about people who weren't getting enough calories either, or people who were losing protein through their damaged kidneys, or people who couldn't digest their food properly because there was something wrong with their pancreas or some other part of the digestive system. I found lots of articles about alcoholics. But I didn't find any articles that supported the idea that protein deficiency is something for vegetarians or even vegans to worry about. Even when I looked up the adverse effects of vegetarian diets, I found articles about vitamin B12 deficiency, but nothing about people getting sick from protein deficiency.

Nor was I able to find any articles about people who had trouble from eating "incomplete" plant proteins. I found reports of people dying from a fad diet whose sole protein source was gelatin. However, gelatin is a processed food that comes from animals.

The Great Protein Fiasco

The scientific evidence has shown since the early 20th century that human protein needs are small and easily met by ordinary plant-based foods. Unfortunately, the people who made nutrition policy got confused by a disease from Africa called kwashiorkor. It was a form of starvation that tended to strike neglected children in very poor populations. Instead of being simply scrawny, these poor children were horribly swollen and their skin was peeling off like flaky paint. The British-trained Jamaican pediatrician who first described this condition suspected that it might be due to a deficiency of protein or one of the amino acids. Today, we still aren't sure what causes kwashiorkor, but the theory that it results from protein deficiency in people who are getting enough calories has fallen out of favor. The people with kwashiorkor aren't getting enough calories, either.

In the late 1950s, the experts at the United Nation's World Health Organization and Food and Agriculture Organization mistakenly concluded that protein deficiency was the single most important nutrient deficiency in the developing world. Their overestimation of the amount of protein people need created an imaginary "protein gap" in the Third World, thus launching what later was called the Great Protein Fiasco. Researchers worked hard to figure out ways to increase people's intake of animal protein in poor countries. This was an economic and environmental and nutritional disaster, for several reasons.

First, the focus on an imaginary protein gap obscured the real problem, which was a shortage of food and thus a shortage of calories and other nutrients. The malnourished people in poor countries are malnourished because they can't afford to eat enough food, not because the foods the local people normally eat is too low in protein. Poor people also tend to depend too heavily on a single staple food, which meant that they are at greater risk for vitamin and mineral deficiencies. Because of poor sanitation, the people in poor countries are also at high risk for parasite infections, which could drain nutrients from their body, thus causing anemia and other problems. None of these problems are caused by protein deficiency, and none of them can be solved by protein supplements.

The attempt to provide protein supplements or to encourage people to grow and eat more meat didn't solve these problems. Instead, they tended to make them worse. The protein supplements tended to be more expensive than people's normal food, so the people would end up being able to afford even fewer calories. Since the problem was lack of calories, the people would be worse off than before. The same thing would happen if people were encouraged to grow and eat more meat. It would be far more efficient to eat grain yourself than to feed it to animals and then eat the animals.

Diet for a small planet

One response to the Great Protein Fiasco of the 1960s and early 1970s was a bestselling book, Diet for a Small Planet. Its author, France Moore Lappe, was concerned about the problem of world hunger. She argued, correctly, that it is far more efficient to eat grains and soybeans ourselves than to feed them to animals and then eat the bodies, milk, and eggs of the animals. However, she was untrained in nutrition and was unaware how easily human beings can get enough of all of the essential amino acids from plant foods.

Lappe came up with a system by which people could combine different plant foods within the same meal, so that together they would provide a higher "quality" of protein. For example, grains such as corn are relatively low in lysine but have relatively large amounts of methionine. beans contain lots of lysine but are relatively little methionine. Theoretically, you could get a better balance of amino acids if you ate beans and corn together in the same meal.

Since Lappe's book became a bestseller, many vegetarians in the United States have worried about "combining their proteins" in order to get a "complete" protein. In reality, corn contains enough lysine and beans enough methionine to meet human nutritional needs. You don't have to eat both of them. And you certainly don't have to worry about eating them in the same meal. In fact, if you work hard to combine plant proteins so that they have the same amino acid balance as animal proteins, you end up with some of the same drawbacks as animal proteins, especially a higher risk for cancer promotion.