If you’ve ever watched Sesame Street, you may remember the song about categories: “One of these things is not like the others. One of these things just doesn’t belong.” That song ran through my head when I looked at the USDA’s My Plate food group system, which features vegetables, fruits, grains, dairy, and protein. One of the foods groups isn’t like the others and just doesn’t belong. Can you guess which one?
Most diet-conscious people today think of potatoes as “a starch.” They think that if you are having potatoes for dinner, you still have to add “a protein” to your meal. Yet potatoes are an excellent source of protein. Scientists have known that since the 1920s because of an interesting experiment that was done in Poland in 1925 and published in 1928 in Biochemical Journal. Thanks to the Internet, you can read the original article for yourself.
The researchers knew that populations that subsisted on a diet based heavily on potatoes seemed to be healthy and remarkably free of scurvy, beriberi, and pellagra—diseases that were known to result from vitamin deficiency. Some earlier work had suggested that potatoes can provide enough protein for human nutrition, and this study was intended to confirm those results.
For 167 days, the researchers fed a healthy young man and a healthy young woman a diet whose only significant source of protein was potatoes. Besides potatoes, the subjects ate fat and salt and a few apples and pears. They could also have the occasional cup of black coffee or tea with sugar.
The subjects thrived on this limited diet. Their health remained good and their weight remained stable, except that the man started losing weight toward the end of the study as he got more serious with his athletic training. Nitrogen balance studies confirmed that they weren’t having any trouble with protein deficiency. Most surprisingly, they didn’t get bored with their monotonous diet! To show that these results weren’t some sort of fluke, look at what happened when someone from the Washington State Potato Commission ate nothing but potatoes for 60 days.
At the end of the article, the authors thanked Dr. Casimir Funk, who directed the experiment. Funk was a superstar in the history of nutrition. In 1912, he published a landmark article describing how he had isolated thiamine, the chemical that is responsible for preventing and curing the deficiency disease called beriberi. That same year, he wrote another landmark article, which suggested that several epidemic diseases were actually the result of a deficiency of some vital chemical that was needed in only tiny amounts. He guessed that, like thiamine, the other chemicals would be amines, so he coined the term “vitamines.” After it turned out that some of these vital chemicals aren’t amines, the “e” was dropped, and they became vitamins.
As this study showed, potatoes contain plenty of protein. So the next time that you think you need to add “a protein” to your meal, eat a potato!
A recent article in the New York Times argued that gorillas stay slim because they eat a high-protein diet. While I’m glad to see someone else point out that a plant-based diet provides adequate amounts of protein, I’m annoyed to see scientists and journalists misunderstand and misrepresent the real significance of this fact. It’s as if they haven’t read the basic literature on nutrition and can’t understand arithmetic.
Yes, the gorilla’s natural diet is high in protein, as a percentage of calories. However, the gorillas’ natural food tends to be low in calories, because the calories are diluted by water and fiber. Gorillas have to eat an enormous amount of food every day to get enough calories. When human volunteers tried to eat a gorilla-style diet for a short period of time to see how it would affect their cholesterol levels, they had to spend more than 8 hours a day eating, just to get enough calories to keep from losing weight during the trial. Gorillas stay slim because of the high fiber content and low fat content of their food, not because of the balance of protein to carbohydrate in their food!
The biggest dietary challenge for a gorilla, as for any leaf-eater, is to get enough calories. When they eat a relatively high-protein diet, they just end up converting the excess protein to sugar and burning it for energy. Unfortunately, protein is “dirty sugar.” Burning protein for energy produces waste products such as urea and sulfuric acid.
People can stay very slim on a high-carbohydrate diet, if it is also high in fiber and low in fat. For example, when Chris Voigt of the Washington State Potato Commission decided to go on a potato-only diet as a publicity stunt, he figured that he had to eat 20 potatoes a day. In practice, he found it really hard to eat his entire potato ration, because potatoes are so filling. As a result, he lost a lot of weight. Even when he made an effort to eat his entire potato ration every day, he continued to lose weight. That’s because a starchy diet improves insulin sensitivity and thus revs up your metabolism. People who eat starchy diets burn more calories than people on fatty diets. Voigt lost 21 pounds during his 60-day potato diet. His cholesterol levels, triglyceride levels, and even his blood sugar levels decreased!
According to the New York Times, Dr. Raubenheimer claimed that modern societies “are diluting the concentration of protein in the modern diet. But we eat to get the same amount of proteins we needed before, and in so doing, we’re overeating.” What nonsense!
Nutrition scientists have known for more than 100 years that human protein needs are modest and are easily met by any reasonable plant-based diet. Also, the societies with the biggest problem with obesity are also the ones with the highest protein intake! Modern societies are consuming too much fat and too little fiber. Animal foods are a big offender, because they contain fat but no fiber and usually no digestible carbohydrate. Refined foods are also a big offender, because they represent the concentrated calories from plants–with the fiber and other wholesome things stripped out.
The take-home lesson from the gorilla story shouldn’t have been that people need to eat more protein. It’s that people need to eat plants. If people don’t want to spend 8 hours a day eating leafy vegetables, they can eat some nice, filling potatoes or other starchy staples along with plenty of vegetables and fruit.
Vitamin D Comes From Sunshine, Vitamin B12 From Bacteria
How can a diet consisting mainly of leaves give gorillas enough protein to grow big and strong? It’s because leaves contain protein. Leaves are low in calories, but a lot of their calories come from protein. In fact, most ordinary plant foods contain more than enough protein to meet human nutritional needs. Nutrition scientists have known for nearly a hundred years that as long as you are eating any reasonable plant-based diet, if you take care of the calories, the protein takes care of itself.
It’s hard even to design a plant-based diet that would be deficient in protein while providing enough calories. You’d have to include nothing but some low-protein fruit, such as apples. Or you could cheat and use sugars and fats that have been extracted from plants, leaving the protein and other nutrients behind.
Not only do plants provide enough protein for human nutrition, the proteins they contain are nutritionally “complete,” as far as human protein needs go. That means that they contain enough of all of the different amino acid “building blocks” that human bodies need.
The only “incomplete” protein you are likely to find on your dinner plate is gelatin, which comes from animal bones. Gelatin is incomplete because tryptophan is destroyed in the manufacturing process. You’d get very sick if you tried to use gelatin as your sole source of protein.
Plant foods also contain the minerals that are essential for human nutrition. Plants absorb these minerals, such as calcium and iron, from the soil. After all, where did the cows get the calcium that goes into their milk? Where did they get the iron that goes into their flesh?
Plants also provide nearly all of the vitamins that are essential in human nutrition. The exceptions are vitamin B12, which is made by bacteria, and vitamin D, which your body can make for itself if you go outside in the sunshine. People who eat a purely plant-based diet are generally advised to take a vitamin B12 supplement. Whether you need a vitamin D supplement depends on how dark your skin is and where you live. Your doctor can do a simple blood test to see whether you have enough of both of these vitamins.