Eating food that comes from plants is a far different experience (and for human beings, a far healthier experience) than eating food that comes from animals.
Animal-based foods contain cholesterol but no starch or fiber. Plants contain starch and fiber but no cholesterol.
When people talk about nutrition, they usually talk about individual nutrients, not about foods.
Unfortunately, this kind of thinking can lead to serious mistakes.
For example, many people will refer to beef or chicken as “a protein,” even though beef and chicken also contain fat.
Most people would never dream of referring to a potato as “a protein,” even though potatoes provide as much protein as you need, along with plenty of other essential nutrients as well as energizing starch.
Yet in all of this discussion of isolated nutrients, most people have somehow missed the point about the fundamental differences between eating food that comes from plants and eating food that comes from animals.
When you look at plant tissue and animal tissue under a microscope, you can see some important similarities, and a few crucial differences.
All living tissue, whether from a plant or from an animal, is made of smaller units called cells. Each of these cells is basically a blob of jelly surrounded by a membrane. This membrane keeps the cell’s insides in, and it controls what can enter or leave the cell.
Unlike animal cells, every plant cell is encased in a tough shell called the cell wall. This cell wall is important. It explains why plants contain fiber but no cholesterol, and why animals contain cholesterol but no fiber.
Plant cells have cell walls, which are made of fiber. Because animal cells don’t have cell walls, they need cholesterol to strengthen their cell membranes. Plant cell membranes have other kinds of sterol, instead.
The cell walls of plant cells are made of cellulose, hemicellulose, and pectin. Technically, these substances are carbohydrates, but animals lack the enzymes to break these complex carbohydrates down into simple sugars.
As a result, these carbohydrates are not broken down before they leave the human small intestine. That’s why we classify them as dietary fiber.
The term fiber is a bit misleading. Not all forms of dietary fiber are made of tiny bits of string. Instead, some of them dissolve in water to form a soft gel.
However, both the coarse and stringy insoluble fiber and the soft, jelly-like soluble fiber provide bulk to the stool. As a result, they help to relieve constipation. The normal bacteria within our large intestine break down some of this fiber.
In the process, they release short-chain fatty acids, such as butyric and propionic acid. Butyric acid is the favorite fuel of the cells that line our large intestine. Propionic acid is carried to the liver, where it has a cholesterol lowering effect similar to that of a station drug.
Although all plant tissue contains fiber, some of the foods that are made from plants contain little or no fiber. Some foods are made from sugar or oil that was extracted from the plant, leaving the fiber behind.
Thus, sugars and oils contain no fiber at all. The refining of grains, such as turning whole wheat into white flour, removes much of the fiber. Juicing of fruits and vegetables removes or at least disrupts a lot of the fiber. To get enough fiber in your diet, you must eat plant foods that are unprocessed or minimally processed.
Animal cells never have a cell wall. For that reason, animal products never contain any fiber. Since an animal cell has no cell wall, it needs a strong cell membrane. To strengthen their cell membranes, animal cells make cholesterol.
Plant cell membranes don’t need to be so tough. They don’t need cholesterol. As a result, plants contain practically no cholesterol. Instead, the cell membranes of plants contain other sterols, called phytosterols. These phytosterols compete with cholesterol for absorption.
So if you eat a purely plant-based diet, you will take in practically no cholesterol. You will even have some trouble in reabsorbing the cholesterol that you secrete into your intestine. As a result, your blood cholesterol level will be so low that your arteries will be clear.
Since plants contain practically no cholesterol, plant-eaters would normally need to be good at conserving the cholesterol that is produced in their liver.
As a result, they would be likely to suffer from a build-up of cholesterol if they ate food that contains cholesterol.
In human beings, cholesterol tends to build up as gallstones in our gallbladders and as atherosclerotic plaque in our arteries.
In societies whose members eat a lot of animal foods, heart attacks due to atherosclerosis are a major cause of death.
Likewise, heart attacks have been a major cause of death among captive gorillas that were fed an
unnaturally rich diet.
In contrast, natural carnivores or omnivores are good at getting rid of excess cholesterol. For example,
dogs never get atherosclerosis unless they have hypothyroidism, which interferes with their normal
If you put a human gallstone into a dog’s gallbladder, the stone would dissolve.
In East Asia, bile from bears has even been used as a drug for treating gallstones in human beings. (A synthetic form of the active ingredient in bear bile is available, so there is absolutely no excuse for taking bile from a bear.)
The fact that human beings are prone to atherosclerosis and cholesterol-containing gallstones suggests that we are not carnivores or even omnivores.
Another important fact about plants is obvious even to the naked eye: plants have pretty colors. Green
plants contain a green pigment called chlorophyll, which works like a solar panel to harness the energy
The plants then use this energy to make sugar out of water and carbon dioxide. The plants
then burn some of that sugar for energy.
They use the rest as raw materials for making other things, such as starch, cellulose, fats, and amino acids.
Photosynthesis involves some high-energy chemical reactions. As a result, some highly reactive
chemicals called free radicals are produced.
Free radicals have a powerful oxidizing effect. To protect themselves against the oxidation caused by free radicals, green plants make their own antioxidants.
Some of these antioxidants are brightly colored, which explains why so many vegetables and fruits are bright green, red, yellow, orange, or purple.
Unlike animal-based foods, bright and colorful fruits and vegetables are an excellent source of antioxidants that can help protect us from the free radicals that our own bodies produce.
Perhaps the biggest difference between plants and animals is that plants stay “planted” in one spot while
animals are “animated”—they move around under their own power.
As a result, animals have to use up some of their energy to carry their energy stores with them, just as an airplane has to burn fuel to carry around its own fuel supply. Like an airplane, an animal needs to store its fuel in a form that provides the most energy for the least amount of weight.
If you look at the calorie counts of different kinds of food, it’s obvious that fat is the most concentrated
source of energy in food. A gram of pure fat provides 9 calories, while a gram of dry sugar or starch
provides only 4 calories.
Of course, the sugar or starch found in plant tissue is seldom dry. Starch tends to absorb water, which is heavy but provides no calories. As a result, boiled rice or potatoes end up providing only about 1 calorie per gram of food. In contrast, fat repels water.
As a result, fat stores are light and easy to carry around. That’s why most of an animal’s energy stores are in the form of fat. The only kind of plant tissue that commonly contains a lot of fat is seeds. But like animals, seeds are built to travel.
For a potato, carbohydrates are the most sensible way to store energy. Since the potato stays planted in one spot, the weight of its energy stores doesn’t matter. What does matter is how much energy gets wasted in converting one kind of fuel to another.
Plant cells can convert carbohydrates to fat; but when they do so, some of the calories get wasted. So if weight doesn’t matter, the plant might as well keep its energy stores in the form of carbohydrates. That’s why so many plant foods are high-carb and low-fat. It is also why many plant-eating animals are adapted to a high-carb, low-fat diet.
When you eat animal-source foods, you are eating a diet that is high in fat and cholesterol and that contains far more protein than you need. It also means that you are eating little or no digestible carbohydrate. The only carbohydrate that you find in large amounts in animal foods is the lactose, or milk sugar, in dairy products. Even then, most of the world’s people lose their ability to digest lactose after infancy. Being able to digest lactose is a mixed blessing. A molecule of lactose consists of a molecule of glucose bound to a molecule of galactose, which is another simple sugar. Small amounts of galactose are found naturally in the human body. The unnaturally large amounts of galactose that result from drinking cow’s milk could increase the risk of cataracts, Alzheimer’s disease, and Parkinson’s disease.
Several human populations do eat an extremely low-carbohydrate diet, more or less all the time.
Examples include some cattle-herding people in Africa and the Inuit (Eskimos) of Greenland, Canada,
From their example, we know that human beings can survive on a low-carbohydrate diet for
years on end. We also know that their diets, which represent an adaptation to a harsh environment, aren’t
Those populations pay a heavy price for that diet, in terms of high rates of osteoporosis and short life expectancy.
Another disadvantage of eating animal-based foods is a higher risk for food-borne parasites and bacterial
infections. If you look at the various kinds of parasitic diseases that can be food-borne, you’ll see that
nearly all of them come from eating some sort of animal-based food.
The few rare exceptions are typically the result of contamination by the droppings of snails, dogs, or other people.
That’s because the germs and parasites that can infect people are specifically adapted to living in animals. Animal bodies are their ecological niche. These germs and parasites typically cannot survive and reproduce without spending at least part of their life cycle in or on another animal.
Food-borne bacterial infections follow the same principle. The bacteria that cause human disease are adapted to living in an animal host.
Typically, they depend on their animal host to provide nutrients that they cannot make for themselves. If you want to grow them in a laboratory, you typically have to feed them some animal product, such as blood.
Thus, animal-source foods readily provide a breeding ground for infective bacteria, while plant-based foods rarely can.
If you caught Salmonella from eating peanut butter, the peanut butter was probably contaminated by rat or pigeon droppings. Salmonella can survive in peanut butter, but it cannot grow or reproduce in it.
If you caught a dangerous strain of E. coli from spinach, it was probably contaminated by manure from feedlot
If you caught infectious hepatitis from eating at a restaurant, it’s likely that one of its employees failed to wash his or her hands after going to the bathroom. A plant-based diet and basic sanitation would eliminate most cases of food-borne infectious disease.
Notice that I said “food-borne infections,” not food poisoning. Most of the gastrointestinal infections that
people refer to as “food poisoning” are really infectious diseases, not true cases of poisoning.
Some plant-based foods can produce true cases of food poisoning. The classic example of true food poisoning
is botulism, which results when bacteria release a dangerous toxin into the food.
This problem typically results in canned foods that were not heated to a high enough temperature for a long enough time.
Another dangerous toxin is aflatoxin, which is produced by a mold that likes to grow on peanuts. Fortunately, both of these problems are rare in countries where the food industry is tightly regulated.