For years, the bestseller lists have been dominated by books urging people to eat plenty of meat and fat but to shun carbohydrates. The Atkins Diet led the parade; but there have been many imitators, such as the Zone, the South Beach Diet, the Paleo Diet, and the Dukan Diet. Even some of the vegan-oriented books encourage people to avoid starches. Yet the scientific evidence shows us that human beings are specifically adapted to thrive on a starchy diet. So I was delighted to see that the title of Dr. John McDougall’s latest book is The Starch Solution. He explains something that nutritional epidemiologists and experts on clinical nutrition have known for many years, namely that human beings stay naturally slim and healthy on a diet based on unrefined starches and vegetables.
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?
Here’s an interesting talk by Nathaniel Dominy, PhD, an Associate Professor of Anthropology at Dartmouth University. He explains the central role of diet in the amazing worldwide success of the human species. If you can’t find enough to eat, you can’t do any of the other things that you would need to do to help you and your children survive.
He makes several important points. One is that human beings are behaviorally “plastic.” He uses the term “plastic” in the scientific sense, meaning that something can take any shape. Our behavior is “plastic” because it can easily be reshaped. As he pointed out, human beings can adapt to many different climates because we have learned to make and wear clothes. We can also learn to eat lots of different foods.
One type of food that is available everywhere except the Artic is starchy foods. All of the energy in our diet comes from sunlight, which green plants use to make glucose out of carbon dioxide and water. Plants then store a lot of this glucose in the form of starch, often in their roots or tubers and in their seeds. Unfortunately, starch is hard to digest. To digest it, we use amylase, an enzyme that converts the starch back to glucose.
Dominy suspects that our ancestors’ ability to recognize and use tuber-forming plants opened up a food source unknown to other primates. “It’s kind of a gold mine. All you have to do is dig it up.”
Dominy points out that, when compared with other primates, human beings have extra copies of the gene for the starch-digesting enzyme amylase. As a result, we have a lot more amylase in our saliva than gorillas or chimpanzees do. People from societies that depend heavily on starchy diets have several more extra copies of the amylase gene and therefore produce a lot more amylase in their saliva. In other words, they have become genetically more efficient at digesting starches. This kind of change can be seen in genetically related populations that have been adapting to different diets for only a few thousand years.
Although humans can and do eat practically anything (we are behaviorally plastic), that doesn’t mean that we are well adapted to a meat-based diet. As he puts it, “Anatomically, we’re not adapted to meat at all…. We simply don’t have the adaptations that you would need to chew meat efficiently. Anyone can look at the teeth of their dog or cat and see what your teeth should look like if you’re going to eat meat. Our teeth don’t match.” Dominy concludes, “The fundamental component of the human diet is a mix of plant foods, with a large amount of starch coming from tubers and seeds.”
In this context, I’d point out that the adaptations to a meaty diet go far beyond the shape of the teeth. Even though dogs often eat a fatty, meaty diet, they generally don’t get high cholesterol or atherosclerosis unless they also have a thyroid disorder that upsets their cholesterol metabolism. In contrast, human beings that eat a fatty, meaty diet are much more susceptible than dogs are to high cholesterol and atherosclerosis. That explains why atherosclerosis is the leading cause of death in the United States but practically nonexistent in societies where people eat a low-fat, plant-based diet.
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!
Here’s an interesting article about the Pima Indians of Arizona.
For about 2000 years, the Pima had been growing corn, beans, and squash on irrigated land in Arizona. As a result, their traditional diet was high in starch and fiber and low in fat (~15% by calorie). After white settlers diverted the Pima’s irrigation water, the Pima had to fall back on the lard, sugar, and white flour supplied to them by the U.S. government. After World War II, the Pima adopted a diet that closely resembles the standard American diet. It is low in fiber and gets about 40% of its calories from fat. As a result, they have horrifically high rates of obesity and type 2 diabetes. In contrast, their blood relatives in Mexico who have kept more or less to their traditional diet have relatively low rates of obesity and diabetes.
Some low-carb gurus have tried to twist the Pima’s story into a justification for eating less carbohydrate and more fat. In reality, it provides strong encouragement for people to eat more starch and fiber and a lot less fat.
I just heard about a “new” diet: the Dukan diet. It’s from France! It promises four steps to permanent weight loss! It promises that people will lose weight while eating as much as they like! The problem is that this “new” diet isn’t really new. It’s just South Beach with a French accent. The quick results from the first phase aren’t from fat loss. Nor will your weight problem be permanently cured by the end of the program, regardless of what Dr. Dukan says. It’s just more false hope for desperate people.
Like many fad diets, the Dukan diet starts with a low-carb phase. As if by magic, this phase causes people to lose several pounds very quickly. Unfortunately, the weight that people lose so quickly does not represent fat. Instead, it represents the loss of the body’s glycogen stores. Glycogen is a starch that is stored in the liver and muscles. When the body needs quick energy, the glycogen is broken down into glucose, which is a sugar that is the body’s favorite fuel.
Like other carbohydrates, glycogen provides about 4 calories per gram of dry weight. However, the glycogen in the body isn’t dry. Each gram of glycogen absorbs about 2.7 grams of water. As a result, each gram of wet glycogen in the body represents roughly 1 calorie of stored energy. If you suddenly deprive yourself of carbohydrates, your body will run through its glycogen stores very quickly, releasing water that will leave the body through the kidneys. You would have to burn up almost 9 times as many calories to lose that much weight from fat.
The rapid weight loss that results from cutting out carbohydrates may be thrilling to the frustrated dieter, but it is meaningless. Nobody is overweight from having too much glycogen, and your body will replace that glycogen and water as soon as it can. What people really want to lose is fat. Besides, losing your glycogen can make you feel crummy. When marathoners “hit the wall,” it’s typically because they’re run out of glycogen.
So the first phase of the Dukan diet or the South Beach Diet will cause a quick but temporary and meaningless weight loss that could end up zapping your energy. If the Dukan diet eventually helps you lose fat, it does so by making your body think that you are starving or seriously ill. During a sudden fast, the body’s supply of carbohydrates is cut off. The body has to rely on its fat stores and the proteins in its tissues instead. A low-carb diet mimics this condition. The body may respond to this emergency by suppressing the appetite. The person may then lose weight the old-fashioned way, by taking in fewer calories than he or she burns up.
The Dukan diet is based on a lie: that people get fat from eating a high-carb diet. In reality, fat is fattening, and starches are slimming. That’s because starch, like glycogen, holds water. It’s actually hard to fatten yourself on starches. For example, consider what happened when the head of the Washington State Potato Commission went on an all-potato diet to protest the exclusion of potatoes from the federal Women, Infants, and Children (WIC) program. He lost 21 pounds in 60 days, even though he was eating about 20 potatoes per day. He also cut his total cholesterol by over a third, and lowered his blood sugar. In other words, he also improved his health.
A starchy diet works on both sides of the weight loss equation. You end up eating fewer calories, because the starchy foods are so bulky. Boiled starches often provide only 1 calorie per gram, whereas fat provides 9 calories per gram. You also end up burning more calories on a low-fat, high-carb diet, because you become much more sensitive to insulin. If you still manage to have a few calories left over, it’s hard for your body to store them as fat. You’d lose about 30% of the calories in the conversion process, so your body just generally revs up your metabolism to burn off the excess. You may end up doing more activity, or simply generating more body heat.
Forget Dukan’s false promises. The only proven way to achieve healthy, permanent weight loss is to switch to a low-fat, high-fiber, high-carbohydrate diet. That’s because it’s the kind of diet that is appropriate to the human body. If you simply train yourself to eating the right kinds of food, you can eat as much as you like and still stay slim.