Why Do Chimpanzees Eat Meat?

Chimpanzees eat meat for two simple reasons: they can catch it and they like it. Chimpanzees are particularly likely to eat meat during the dry season, when shortages of the foods that normally make up the bulk of theirdiet cause them to lose weight. Although the meat may be a useful source of calories during the dry season, wild chimpanzees don’t need to include meat or any other animal-based food in their diet to fulfill their needs for protein or any of the amino acids. In fact, plants provide all of the nutrients that are known to be essential for a chimpanzee, except for vitamin D (which they get from the abundant sunshine in Africa) and vitamin B12 (which comes from bacteria).

Many people think that I am silly for asking where gorillas get their protein. They tell me that I should talk about chimpanzees instead. Often, they inform me that chimpanzees are far more similar to human beings than gorillas are, as if I couldn’t tell that just by looking. These people are missing my point: gorillas are the largest and most powerful living primate and yet are the closest to following what human beings would consider a vegan diet. Chimpanzees and human beings don’t need to eat meat to grow up big and strong because gorillas grow up to be far bigger and stronger without it. Lawyers may recognize this as an a fortiori argument.

If a male gorilla, whose digestive system is practically identical to a human being’s, can get enough protein from vegetables to grow to weigh more than 400 pounds and be ten times as strong as a man, why shouldn’t I expect that a relatively puny human Olympic weightlifter could also get enough protein from a plant-based diet? My intent is to ridicule the Four Food Groups dogma that I was taught in sixth grade.

Gorillas don’t hunt or fish, and they don’t keep cows or chickens. As a result, they don’t eat meat or fish, dairy products or eggs. The only animal-source food they eat is “the other, other white meat”: termites, slugs, and other creepy-crawlies. These foods would make an insignificant contribution to the gorillas’ protein intake, which is already high because protein accounts for a high percentage of the calories in leaves.

Bugs and slugs could be a useful source of vitamin B12, a micronutrient that is made by bacteria in their intestines. Vitamin B12 is also produced by bacteria in a primate’s gastrointestinal tract. However, the vitamin may be produced so far along in the intestinal tract that it isn’t absorbed efficiently. No plants make vitamin B12, but gorillas and chimpanzees can probably get enough vitamin B12 from the bacteria in the bugs they eat and in the dirt that clings to their food. Plus, apes are not meticulous about washing their hands, if you get my drift. If you are worried about getting enough vitamin B12, you don’t have to eat dirt or bugs. You can get it in a nice, clean tablet instead.

I don’t ask where chimpanzees get their protein because chimpanzees do eat some meat. Chimpanzees probably eat less meat than just about any human population other than Buddhist monks. Nevertheless, many people want to use chimpanzees’ meat consumption as an excuse for humans to eat meat.

The fact that chimpanzees’ meat consumption is largely seasonal goes far toward explaining why human beings have always eaten meat. Chimpanzees are most likely to eat meat during the time of year when they are losing weight because their usual foods are in relatively short supply. People think of meat as a source of protein, but it’s mainly a source of calories, especially from fat. Meat is also a good source of sodium, which is in relatively short supply in the chimpanzees’ fruit and vegetable diet.

The fact that chimpanzees eat the most meat during times of food shortages suggests that their food choices follow a pattern that biologists call optimal foraging theory. Animals try to get the most calories for the least effort and without getting hurt. Optimal foraging theory explains why chimpanzees eat meat but gorillas don’t, and why chimpanzees eat more meat during times of food shortage.

Chimpanzees are mainly fruit eaters, but they also eat a lot of vegetables. The problem with fruit is that it’s seasonal. Worse yet, a fruit tree represents a rich enough source of calories that animals will fight over it. When fruit is scarce, chimpanzees can use the skills they developed in fighting over the fruit to engage in predatory behavior. Also, chimpanzees are small enough and fast enough that they are reasonably good hunters.

Gorillas, on the other hand, mainly eat leaves. There are generally plenty of leaves to go around, and a leafy plant is generally so poor in calories that it’s not worth fighting to protect. To subsist on leaves, however, you have to eat an enormous volume of food. Since leaves are so low in calories, leaf-eaters have to be good at conserving their energy. That’s why gorillas have such a placid disposition. For a gorilla, hunting is simply not worth the effort. They are too big and slow to catch very much, and they’re large enough that they’d risk injury if they got too reckless.

Chimpanzees use twigs to fish for termites, and gorillas don’t. Some people think that this fact means that chimpanzees are smarter than gorillas. I don’t. If you are a juvenile gorilla or a pregnant or nursing female gorilla, you don’t need to mess around with a little bitty twig to get a few termites. All you have to do is wait for the silverback to knock over a rotting tree. Then all of you can eat as many termites as you’d like.

Some people have argued that the balance between animal and plant foods in a hunter-gatherer society’s diet represents the optimal balance for human nutrition. I think that’s idiotic. Hunter-gatherer peoples (or should I say, gatherer-hunter peoples) tend to follow optimal foraging theory just like any other opportunistic feeder. Their goal is to survive in the short term, not to avoid breast or prostate cancer in middle or old age. The main threat to their short-term survival is starvation.

Meat represents a concentrated source of calories. The fact that a relatively high percentage of these calories comes from protein is actually a disadvantage. Hunting peoples prefer the fattiest foods. People who end up having to subsist on extremely low-fat meat, such as rabbit, are prone to a problem called fat-hunger or rabbit starvation. This problem probably results from a diet that has too much protein and not enough carbohydrate or fat. On a low-carb diet and during starvation, the body has to make its sugar supply out of protein. Perhaps the body can make only so much sugar out of protein. As long as you are eating enough fat to meet most of your energy needs, your body can make enough sugar out of protein to feed your brain. If you were eating protein but not enough fat or carbs, you could end up in serious trouble. So you could end up in trouble from a diet that is too high in protein. In contrast, it is practically impossible to avoid getting enough protein, as long as you are eating enough unrefined plant foods to get enough calories.

Famine is not a significant cause of death in the United States. In fact, people in the United States are far more likely to die of the diseases of affluence, such as heart disease and cancers of the breast and prostate. Animal-based foods and fatty processed foods are the main contributing causes of the diseases of affluence. The ability to use animals for food may have helped human beings survive to the modern era, especially in the Arctic, but animal-based foods are a major cause of death and disability in the United States today. Think about that the next time you hear someone promoting a “Paleo” diet.

No, It’s a Low-Fat, High-Fiber Diet That Keeps Gorillas Lean!

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.

We’re Making the Gorillas Sick! Stay Away From Them!

When I was a child, I saw that the gorillas, unlike all the other animals at the Columbus Zoo, were behind glass. My parents said that this was to keep the gorillas from catching diseases like tuberculosis from the people who came to see them.

Gorillas look almost human because their genes are strikingly similar to ours. Chimpanzees and bonobos look even more human-like because their genes are even more like ours. The more DNA you have in common, the more likely it is that you’ll be susceptible to the same bacteria and viruses. Human beings probably caught the first cases of AIDS from chimpanzees. Now there is a report from the U.S. Centers for Disease Control and Prevention that endangered wild gorillas are catching a deadly virus from human beings! They are probably catching the disease from the ecotourists who go to see them!

On one hand, ecotourism seems to be necessary to help protect the gorilla habitat. On the other hand, the diseases that the ecotourists bring with them could be deadly to the gorillas.

Why Gorillas, Why Not Chimpanzees?

Many people have asked me, why do you ask where gorillas get their protein, when our bodies and our body chemistry more closely resemble those of chimpanzees? My answer is that gorillas are much bigger and more powerful than chimpanzees. Last night, I saw a museum exhibit that compared a gorilla skull to a chimpanzee skull and a human skull. (They might have been models. It was hard to tell.) The gorilla skull was huge! The chimpanzee skull was about the same size as a human skull.

The other reason is that gorillas eat a much more strictly plant-based diet. Chimpanzees hunt once in a while, and they often eat their kill. Even so, they still eat a lot less meat than just about any human population. Nevertheless, I was afraid that the fact they eat a little bit of meat now and then would muddy the waters.

My point is this. Most of the really big and powerful land animals got big and powerful by eating plants. They don’t worry about getting a protein deficiency on a plant-based diet, and neither should you.


(Image courtesy of Mahlatini Luxury Safari, https://www.mahlatini.com/gorilla-trekking-safaris/)

Humans and Gorillas Can Get Gout, But We Can Both Get By With Very Little Salt!

Gouty arthritis results from the buildup of crystals of uric acid in the joints.

People who eat a lot of meat are at risk for gout—one of the most painful conditions known to medical science. Gout results when crystals of a uric acid salt build up in the joints. These crystals can also build up in the urinary system, producing kidney stones—another of the most painful conditions known to medical science. A recent theory suggests that our high risk for gout is a side effect of an adaptation that enabled human beings, gorillas, and the other great apes to survive a shortage of sodium.

Although eating meat and seafood causes gout in people, it doesn’t cause gout in a natural carnivore like a cat. That’s because cats, like most mammals, produce an enzyme called uricase, which breaks uric acid down into something that dissolves easily in water and passes right out through the kidneys. Human beings and the great apes are practically the only mammals that can’t make uricase. This fact suggests that people, like gorillas, should probably be eating a highly plant-based diet.

In the wild, apes are free from gout because their plant-based diet is low in purines, which the body converts to uric acid. Fruit and vegetables are also mildly alkalinizing, and the mild metabolic alkalosis enables the blood to keep more uric acid dissolved. So the great apes can live gout-free even though they can’t make uricase. Similarly, human beings can avoid gout simply by eating a plant-based diet with a heavy emphasis on fruit and vegetables.

It’s surprising that human beings and the great apes can’t make uricase. We’re practically the only mammals that don’t. The gene for uricase has survived almost unchanged through hundreds of millions of years of evolution. That’s generally a sign that the gene does something important. Yet the lack of uricase might actually be an advantage for wild apes. The extra uric acid in their blood might enable them to survive on a diet that would otherwise be dangerously low in sodium.

As we’ve seen, gorillas eat a very low-sodium diet. Meat-eaters don’t run a risk of sodium deficiency, because meat and other animal-based foods are high in sodium.

Where Do Gorillas Get Their Vitamin B12?

Termites: The Other, Other White Meat

Vitamin B12 is one of the two nutrients that are essential for human beings but aren’t available from a purely plant-based diet. The other is vitamin D, which isn’t truly a vitamin but is a hormone that your body can make for itself if you get some bright sunshine on your skin. Gorillas live in Africa, where there’s no shortage of sunshine. The interesting question is where do they get their vitamin B12? Evidently, they get it from the insects and other creepy crawlies that they eat. Their favorites are termites—the other, other white meat.

As you can see, the gorillas just dismantle the tree where the termites are. That’s probably why they don’t bother using tools to fish for termites, as chimpanzees do:

Except for vitamin D and vitamin B12, plants provide all the essential nutrients that people need. Plants contain minerals, such as calcium and iron, which they have absorbed from the soil. Plants contain all of the other vitamins and essential amino acids, which they have made for their own purposes. Plants are also the original source of the essential fatty acids. However, plants don’t make vitamin B12, and neither do animals. All of the vitamin B12 in nature comes from bacteria.

Some plant-eaters get their supply of vitamin B12 from the bacteria in their own digestive system, as long as they are eating something that contains the element cobalt. (Vitamin B12 contains cobalt). Cattle and sheep are particularly good at getting vitamin B12 from their own gut bacteria. They have a lot of bacterial fermentation going on in their stomachs, so the vitamin B12 is made before the food passes through the part of the intestine where the vitamin B12 gets absorbed. Such animals are called “foregut fermenters.”

Other species, including rabbits and gorillas and human beings, are “hindgut fermenters.” Their gut bacteria make vitamin B12, but only after the food has passed through the part of the intestine where the vitamin B12 can get absorbed. Rabbits solve this problem by eating some of their own droppings. Wild mountain gorillas sometimes do the same thing, usually during periods of bad weather. Captive gorillas do it a lot more often, possibly because they are bored.

On the other hand, gorillas and human beings can eat foods that already contain ready-made vitamin B12. For gorillas, that means tasty, tasty termites, which get vitamin B12 from their own gut bacteria. Modern human beings who don’t want to eat termites, or any other animal products, can get their vitamin B12 from a nice, clean, and very cheap supplement. As long as their gastrointestinal system is healthy, people can even take their vitamin B12 by mouth. Vitamin B12 shots are useful for people who have trouble absorbing vitamin B12 from their food, because of gastrointestinal disease.

How Gorillas Celebrate Christmas–With Brussels Sprouts!

Just Make Sure You Stay Upwind of Them

At Christmastime last year, the Chessington World of Adventures, in Surrey, England, gave their gorillas some Brussels sprouts. The gorillas loved them, but the aftereffects horrified the zoo visitors.

Gorilla keeper Michael Rozzi said: “We feed the gorillas Brussels sprouts during the winter because they are packed with vitamin C and have great nutritional benefits. Unfortunately, an embarrassing side effect is that it can cause bouts of flatulence in humans and animals alike. However, I don’t think any of us were prepared for a smell that strong.” The gorillas didn’t seem to care, nor did any of the gorillas ask anyone to pull their finger. The zoo keepers solved the problem by giving the gorillas their Brussels sprouts after closing time. On Christmas Day, when the zoo was closed to the public, the gorillas got to eat Brussels sprouts all day long. It was a solution that worked for everyone.

I eat a lot of Brussels sprouts in the winter, and I eat other members of the cabbage family and lots of beans year-round, but I never have a gas problem. I’m grateful for that, but it means I can’t use myself as a subject to test possible remedies. Some people recommend Bean-o, and others recommend spices and herbs such as cumin, fennel, caraway, dill, peppermint, chamomile, sage, and thyme.

Many people who think that they hate Brussels sprouts really only hate overcooked Brussels sprouts. Overcooking releases a stinky sulfur compound called sinigrin. Try cooking your sprouts for only 6 to 7 minutes, and see if that makes a difference. The sinigrin will stay put, until you digest the sprouts.

Sinigrin may stink, but it’s probably good for you. It evidently causes cancer cells in the colon to commit suicide, which could help to explain why populations that eat a lot of cabbage and other members of the Brassica family, including Brussels sprouts, have a low risk of colon cancer.

Why Gorillas Are So Gentle

The Upside and Downside of Living on Leaves

All of the great apes are plant-eaters. Even chimpanzees, which occasionally hunt and kill small animals and eat them, still eat less meat than nearly any human society. Yet the various great ape species fit into different ecological niches, so they focus on different kinds of plant foods. Chimpanzees are mainly fruit eaters. Although gorillas will eat fruit and nuts whenever they’re available, they mainly eat leaves.

The fact that gorillas mainly eat leaves explains a lot about their behavior and social structure. Leaves don’t run away, so there’s no need to chase them. Leaves are so abundant in the gorilla’s habitat, and so low in calories, that it’s pointless to fight over them. A tree full of ripe fruit or nuts is another matter, entirely. In general, I’d expect animals that mainly eat leaves to be nicer than animals that mainly eat fruit, because they have less to fight over.

Gorillas face the same kinds of challenges as any animal that specializes in eating leaves. Here are a few of those challenges, as explained by Fiona Sunquist (The strange, dangerous world of folivory. International Wildlife; January-February, 1991; pages 4-10):
The demands of living on low-energy and often poisonous food means that most folivores live close to the limit of their energy supply.
  • They must conserve energy wherever possible, and this often translates into being very slow.
  • It is no coincidence that the sloth, the world’s slowest mammal, is a folivore.
  • Besides being slow, folivores also spend much of their time resting.


All this suggests that if you want to be a marathon runner, you’ll want to eat something besides leaves–ideally something starchy. If you simply want to be thinner, you might want to try eating more leaves.