Koalas have it easy. What to eat? No worries: they eat eucalyptus leaves, period. We humans have it tougher. Ever since Eve and the apple, we have had to make decisions about what to eat. Today we are constantly bombarded with conflicting advice about food. “Eat fish because it’s a great source of omega-3s.” “Don’t eat fish because it contains toxic mercury.” (Actually both of those statements are true, so we need to quantify the actual content in specific varieties of fish and carefully consider the risk/benefit ratio.)
Fad diets and “miracle” diet supplements promise to help us lose weight effortlessly. Different diet gurus offer a bewildering array of diets that promise to keep us healthy and make us live longer: vegan, Paleo, Mediterranean, low fat, low-carb, raw food, gluten-free… the list goes on. Obviously they can’t all be right. Food myths abound, often supported by the strongest of convictions and emotions. What are we to believe?
We live in the Information Age. Unfortunately, bad information comes mixed with the good. The only reliable guide to reality is science, but when it comes to food, there’s a problem. It’s hard to do a gold standard double-blinded randomized controlled study on diet. We could learn a lot if we could divide infants into two groups, insert feeding tubes, pour competing diets directly into their stomachs throughout their lifetimes, and see which group lived longer and had fewer illnesses. But that just isn’t feasible. So we have to rely on less conclusive forms of evidence. We can compare two groups who eat different diets (such as vegans v. meat-eaters, or Mediterraneans v. Americans), but those groups almost always differ in other ways that affect results, ways that we didn’t think to control for. We can ask people what they eat, but we can’t trust their answers to be accurate; people tend to misremember, to misestimate portion sizes, and to misreport what they eat in the direction they think the researcher will approve of. We can tell people what to eat for a study, or even provide the food we want them to eat; but compliance is a problem, and studies are time-limited.
It’s not hopeless, because we can combine less ideal types of research and reach a reasonable conclusion if the evidence from all the avenues of inquiry converges. We didn’t need lifelong blinded trials to learn that smoking causes cancer: the evidence from animal studies, analysis of tobacco for carcinogens, various kinds of studies comparing smokers to nonsmokers, etc., all pointed in the same direction. If the evidence from diet studies were as coherent, as consistent, and as strong as the evidence from tobacco studies, science would have reached a consensus by now, and we would know which diet is optimal. Unfortunately, the evidence for different diets is inconsistent or lacking. If anyone claims to know how you should eat, you can pretty much guarantee they are wrong. We have hints, but we don’t have a definitive answer about which diet is best, and we have pretty good evidence that some of the pronouncements on diet are just plain wrong.
What we Know is True
Science has given us a lot of reliable information about nutrition. It took a while to realize that “our daily bread” alone wouldn’t keep us healthy. As late as the 19th century we had no explanation for scurvy, beriberi, kwashiorkor, and other nutritional deficiency diseases.
Vitamins were not discovered until the 1920s. Today we know that we need six categories of nutrients: proteins, fats, carbohydrates, vitamins, minerals, and water. We know that some nutrients like vitamin K are stored in body fat for future use while excess amounts of others, like vitamin C, are excreted in the urine and must be replenished more frequently. We can measure blood levels and body stores of various nutrients. We know there are 14 essential vitamins and 17 essential minerals plus a few ultra-trace minerals that the body requires in only the tiniest amounts. We have identified the nine amino acids in protein that are “essential” in diet—the ones that the body can’t synthesize: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. (Serendipity led early Mexicans to a diet based on corn and beans, which together provide all the essential amino acids.) We know that there are two components of fat that are essential fatty acids for humans: alpha-linoleic acid (an omega-3 acid) and linoleic acid (an omega-6). We know the approximate daily requirements of every nutrient, and they are provided on package labels as Recommended Daily Allowances (RDAs). Dietitians can analyze the nutrient content of a person’s diet and can prescribe appropriate diets for various health conditions like diabetes. We understand nutritional requirements well enough that we are able to provide total parenteral nutrition intravenously to patients whose gastrointestinal tract is unable to function for some reason.
We know that the gastrointestinal tract digests what you eat and breaks it down into its component nutrients. The original source of the nutrients is relatively unimportant. Eskimos get most of their nutrients from raw meat and blubber; the Maasai eat raw meat, raw milk, and raw blood from their cattle; vegans eat no animal products of any kind. Throughout human history, people have eaten a wide variety of diets, some rich in plant foods, some poor in plant foods and rich in animal foods. People can thrive on a wide variety of diets; they can even live on raw meat alone. It has all the nutrients we need, even vitamin C, which is not present in cooked meat because it is destroyed by heat. (Not that I would recommend a raw meat diet!) Those are things that we know are true.
What We Know is Not True
There are other things people think they know about diet that simply aren’t true. Some people claim that a proper diet will prevent all cancer and even cure existing cancers. The scientific evidence does not support that claim. The American Cancer Association estimates that a healthy diet could prevent only around a third of all cancers. There’s no way diet could prevent the 5-10% of cancers that are genetic, the 25-30% that are caused by tobacco, the 15-20% that are caused by infection, or the 10-15% that are caused by other environmental factors such as sun exposure, radiation, and environmental carcinogens. Some foods reduce the risk of cancer, others increase it. Foods that have shown the strongest correlation with reduced risk of cancer include broccoli, berries, tomatoes, and garlic. The dietary factors that are most strongly associated with cancer include overeating (obesity), alcohol, high intake of red meat and processed meats, and low intake of fruits and vegetables.
Since the days of Hippocrates, people have thought of food as medicine. Recently, one naturopath called it the “most powerful drug,” and some have claimed that all disease could be prevented and/or cured by just eating right. Wouldn’t that be nice! Too bad it’s only wishful thinking. A nutritious diet is essential to health, but food is not medicine except when it is used to correct a dietary deficiency, like citrus fruits for scurvy to correct a lack of vitamin C.
The changing advice about cholesterol and heart disease has confused the public and engendered distrust of science. At first, consumers were told to avoid eggs and other sources of dietary cholesterol; product labels trumpeted “contains no cholesterol.” Then further research showed that cholesterol in the diet had little effect on blood cholesterol levels and on the incidence of heart attacks, and recommendations evolved to become more precise as we learned more. We were advised to worry less about dietary cholesterol and worry more about total fat intake, then to avoid saturated fat, and finally to avoid trans fats and not worry so much about the other fats. While it can be frustrating to see science change its mind like this, we should appreciate that science follows the best currently available evidence, in contrast to diet myths that were never based on any credible evidence and never change in response to new evidence.
Opinions about the healthiest diet for humans often rely on arguments from evolution: we should eat what our ancestors evolved to eat. There are some serious pitfalls in that reasoning. There was not one Paleolithic diet: there were many. Our ancestors ate whatever they could get. If they lived near water, they ate fish and shellfish. If they were good hunters in an area with plentiful game, they ate meat. If hunting was not very productive, they relied on gathering food from plants. If fruit was in season, they picked fruit. If nothing was ripe, they dug roots. If there was a plague of locusts, they ate the locusts. Like my smart-aleck brother, they were on a “seefood” diet: “When I see food, I eat it.” Studies of traditional diets from around the world have shown a wide variation in macronutrient content, from 30 to 78% carbohydrate, 7 to 40% fat, and 15 to 50% protein. Archaeological evidence indicates that different human groups thrived on a great variety of diets. Our ancestors would not have been able to migrate to new continents or to survive Ice Age climate changes if they had not been able to readily adapt their diets to what was available.
Our homeostatic mechanisms can maintain an equilibrium across a wide range of nutritional inputs. If we eat more vitamin C than we need, we pee out the excess; if we don’t eat enough cholesterol, our body manufactures the rest of what it needs. There are hints that exercise may be able to compensate for some of the harmful effects of nutritional deficiencies by activating antioxidant defenses.[i]
The Paleo Diet: What is “Natural”?
Paleolithic diet proponents argue that eating grain is not “natural,” but there is archaeological and other evidence indicating that humans were already eating grains well back in Paleolithic times, long before the development of agriculture. In reality, most of the foods that our Paleolithic ancestors ate no longer exist. Instead of big ears of corn, they gathered tiny teosinte ears. Ancient avocados had only a few millimeters of edible flesh surrounding a huge pit. Ancient chickens were tough and scrawny, and their eggs were small. We have modified essentially all of our foods by selective breeding. Our ancestors gladly traded their “natural” diet for a better, “unnatural” one. Paleo is not healthier. It consists of 50% meat, and studies have shown that increased meat intake increases the rate of death.[ii] It recommends avoidance of dairy foods, but a 2010 review found that eating more dairy products was associated with a lower risk of heart disease, stroke, diabetes and death.[iii] And heavy consumption of whole grain is associated with a lower death rate.[iv] The Paleo folks explain away all that scientific evidence by accusing researchers of being controlled by the food industry. I don’t think industry is powerful enough to corrupt all the scientists studying nutrition.
If evolution teaches us anything, it’s that humans are remarkably adaptable, and that we have continued to evolve since the Paleolithic. Our early ancestors were all lactose intolerant as adults; babies produce lactase so they can digest breast milk, but adults lose that ability. Now a substantial part of the population continues to produce the lactase enzyme throughout their lifetime. Part of the human population has evolved to take advantage of a new source of nutrition: the milk from dairy cows. After the introduction of dairy farming in northern Europe, the prevalence of lactase-persistence genes rose to over 80% of the population, while in other parts of the world where dairy farming was not practiced it remained essentially zero.[v] Similarly, populations with high–starch diets have more copies of the gene for amylase (needed to digest starch) than those with low-starch diets.[vi] These are examples of evolution in action; we have evolved beyond the Paleo days, so it is not logical to revert to Paleo eating habits.
Travelers commonly develop GI upsets as they encounter new foods and new microbes; with prolonged residence in a new area, they adapt through changes in their intestinal flora and through other mechanisms. In diet studies, Dr. Antonis Kafatis found that when Cretans and British subjects were fed olive-oil-based meals, the Cretans had faster clearance of blood lipids, but after 3-4 weeks the British subjects’ clearance became equal to that of the Cretans.[vii]People have a fixed set of genes, but the expression of those genes can change when they change their diet. When African Bushmen were switched to a high-starch European diet, the amylase levels in their saliva increased fourfold.[viii] Epigenetics turns genes on and off and can sometimes transmit those changes in gene expression to the next generation or two.
We evolved to become exceptionally skilled omnivores with the intelligence and inventiveness to create technology that increases food production and creates new food sources. One of those technological advances was cooking. Advocates of the raw food diet have an underlying vitalistic philosophy; they believe there is some kind of life force energy in raw foods (although they don’t go quite as far as the “live food” advocates). They try to justify their ideology with science. They argue that fire was a late discovery and cooking is not “natural.” They argue that cooking destroys nutrients and destroys the natural enzymes in foods, but we know that digestion disassembles those enzymes so they don’t act in the human body. And cooking actually increases the availability of many nutrients. They argue that cooking produces toxins, and there is some truth to that, especially for fried foods, but the amounts are small. There is no evidence that a raw food diet is healthier. In fact, cooking was a discovery that allowed humans to take advantage of foods that would otherwise have been indigestible, to spend less energy chewing, and to extract more nutrients from some foods. And cooking has been around for longer than they think, with current estimates going back as far as a million years or more.[ix] It has even been suggested that cooking provided the increased energy to facilitate the evolution of larger brains. It could be argued that we “should” do whatever evolution has insured that we “could” do, such as agriculture, cooking, selective breeding, and food processing.
Cooking is a form of food processing. Processed foods are typically demonized, but they can be either good or bad. According to the IFIC (the International Food Information Council), “processed foods” encompass four categories: (1) foods that are processed to preserve freshness (like canned salmon and frozen fruits and vegetables); (2) foods combined with sweeteners, colors, spices, or preservatives (like rice, cake mix, salad dressing, and pasta sauce); (3) “ready-to-eat” foods (like breakfast cereal, yogurt, rotisserie chicken, granola bars, cookies, crackers, and sodas); and (4) prepared foods (like deli foods, frozen meals, and pizzas). The IFIC further identifies a “minimally processed” food category, which includes washed and packaged fruits and vegetables, bagged salads, and ground nuts.[x]
We humans have always processed our foods. We seldom just grab an animal or plant and devour it without any preparation. Most of the food we eat is processed in one way or another, by washing, chopping, grinding, cooking, canning, freezing, drying, skinning, smoking, adding preservatives so foods will stay edible longer, etc. Food processing is not inherently evil. It should be considered on a case-by-case basis; processing that adds sugar or toxins or removes nutrients is not healthy, but other kinds of processing increase food availability and nutritional value.
Dietary Morals and Weight Loss Myths
There is a moral aspect to dietary recommendations. In his book Diet Cults,[xi] Matt Fitzgerald argues that a propensity to make moral judgments based on others’ food choices began as a practical way to encode trial and error knowledge about safe foods and later became hardwired into human behavior because of the survival advantage of group cohesion. Our tribe vilifies those other tribes who “don’t eat right.” Taboo foods that are perfectly healthy have been encoded into religious rules like halal and kosher because taboos serve to strengthen group identity. Today’s environmentalists and animal rights activists are almost religious in their zeal to condemn those who eat in ways that they consider bad for the environment or for animal welfare.
Peer pressure is powerful but is not necessarily in line with truths about diet. Even without explicit rules, we tend to eat like our parents or our social groups. Who is attracted to the Paleo diet? Mostly men (the virile caveman image?). On the other hand, 60% of vegetarians are women (appeal to compassion?). Both are attractive as a form of rebellion and rejection of artificial modern life. People believe they have chosen a diet rationally, but they really choose for social and emotional reasons and then try to justify their choice with post hoc reasoning.
One of the major reasons people adopt diets is to lose weight. Pretty much all weight-loss diets succeed in the short term but fail to keep the weight off permanently. Studies have shown that people who lost weight and kept it off did so by using all kinds of different methods; no one diet was more effective than another. Motivation was the key. Common factors for those who kept the weight off included keeping a food diary, self-weighing, exercise, and consistency (not varying eating habits on weekends and special occasions).
All diets are essentially ways to trick yourself into tolerating a lower calorie intake. Different tricks work better for different people. Satiety is important; bulky, low calorie density foods provide satiety with fewer calories. A low fat diet helps some people control calories because fat contains nine calories per gram while protein and carbs provide only four calories per gram. If you eat fewer calories than you burn, you will necessarily lose weight. A reduction of 500 calories a day equates to the loss of a pound a week. It’s simple physics in principle, but it can be diabolically difficult in practice. Some people argue that calorie counting won’t work because not all calories are equal. It’s true that there are differences in absorption, satiety, metabolism, and effect on hormones, but in practice those differences are too small to matter very much.
Low carb diets have been recommended both for weight loss and for health. High carb intake has been blamed for the obesity epidemic, but studies have found that, if anything, people who eat more carbs are less likely to be overweight.[xii] Comparison of weight loss diets shows that it is the calorie restriction that matters, not the macronutrient content.[xiii] In some studies, people have lost weight more rapidly with low-carb, but the long-term results are no different. Low-carb can be a convenient way to reduce calorie intake; but the initial enthusiasm for diets like the Atkins diet and the South Beach diet is waning, and some people prefer other diets that work just as well. Some athletes bought into the fad and tried to reduce their dependence on carbohydrates, but the diet of the world’s best endurance athletes (from Africa) is 75% carbohydrate. Gary Taubes, in his impressive 640-page tome Good Calories, Bad Calories,[xiv] argues that the official low-fat diet recommendations for heart disease prevention were not based on good science and had the unintended effect of making people eat more carbohydrates, so low-fat diets indirectly caused the obesity epidemic. He advocates low-carb not just for weight loss but for prevention of the so-called diseases of civilization (obesity, heart disease, diabetes, cancer, Alzheimer’s, etc.). He marshals an impressive mass of data about insulin resistance, fat storage, the metabolic syndrome, inflammation, and other factors to support his thesis. He doesn’t say much about other research that contradicts his thesis, and he admits that his ideas haven’t yet been properly tested against competing ideas; but he urges readers to adopt his diet recommendations without waiting for the testing to be done. So in essence, he is doing exactly what he vilified the low-fat advocates for doing, advising population-wide dietary changes based on inadequate evidence. Chris Voight (executive director of the Washington State Potato Commission) did an informal test. He went on a potatoes-only diet for 60 days; according to low-carb theories he should have gained weight and raised his blood sugar, but instead he lost 21 pounds and lowered his blood sugar.[xv] His cholesterol and triglyceride levels dropped too. He felt well and had plenty of energy, although he got awfully tired of eating 20 potatoes a day.
I would love to see Gary Taubes in a debate with Colin Campbell, a man who believes just the opposite and thinks he has just as good evidence. Campbell wrote The China Study,[xvi] subtitled The Most Comprehensive Study of Nutrition Ever Conducted and the Startling Implications for Diet, Weight Loss, and Long-term Health. For him, carbs are not the enemy, animal protein and dairy products are. He relies on epidemiologic studies from villages in China and arguments based on laboratory research. He claims that heart disease can be prevented and even reversed by a healthy diet, but the evidence he provides is inadequate to support that claim. He advocates a vegetarian diet devoid of all animal protein and dairy products. Like Taubes, he marshals an impressive mass of data but fails to include other data that tend to discredit his thesis. Obviously, he and Taubes can’t possibly both be right; but they could both be wrong, or even wrong in some aspects and right in others.
Good and Bad Foods
Some foods have more of certain nutrients than others, but the idea of “superfoods” is a myth. No food is a perfect source of all nutrients. Yes, spirulina has an impressive array of nutrients; but spinach has even more. Superfood lists disagree with each other and can include as many as 200 foods. If these were all superfoods, almost all foods would be superfoods, making the concept meaningless. So many healthy foods are left off the lists that you could eat a healthy diet while avoiding everything on the list. There’s no advantage to eating special, expensive, or exotic foods high in certain nutrients if you can easily get the same nutrients from other foods that are cheaper and easier to find.
No foods are perfectly good, and no foods are perfectly bad. Several supposedly healthy diets prohibit coffee, but the bulk of current evidence indicates that coffee is healthy. A 2012 study in the New England Journal of Medicine found that regular coffee drinkers were 10% less likely to die over the next 13 years.[xvii] The caffeine in coffee is a stimulant, but coffee (whether caffeinated or decaffeinated) is also the number one source of antioxidants in the American diet.[xviii] Coffee drinkers are less likely to develop certain diseases.
Sugar has been demonized—even called “addicting”—but there’s no reason it can’t be part of a healthy, nutritious, calorie-controlled diet. Fructose has been demonized, too, especially in the form of high-fructose corn syrup. Table sugar is a combination of one molecule of fructose and one of glucose. So it is 50% fructose. High-fructose corn syrup is not much higher, it’s 55% fructose, and its increased sweetness allows using fewer calories for the same effect. And it’s cheaper. Apples and peaches have higher percentages of fructose than high-fructose corn syrup.
Even alcohol, despite the harm it does, can be part of a healthy diet when used in moderation; moderate alcohol intake is more effective at reducing the risk of heart attacks and strokes than other interventions like diet and blood pressure control. It is the second-best way to reduce cardiovascular risk after smoking cessation.[xix] The benefits of red wine have been attributed to resveratrol, which has been put into pills and hyped way beyond the scientific evidence. Of course, alcohol can’t be generally recommended for health because of the dangers of intoxication and addiction.
Water is essential to life, but too much is as bad as too little: people can die of water intoxication. It is important for athletes to replenish lost fluids, but overhydration has killed marathon runners. There are many myths about dehydration, from the myth that we need to drink 8-10 glasses of water a day to Dr. Batmanghelid’s “Water Cure” and his claim that dehydration is the main cause of disease.[xx] It isn’t. It doesn’t cause all those diseases, and it doesn’t cause most of the symptoms people attribute to it. For most people, in most situations, it is sufficient to drink when you feel thirsty, and the source of the water is not important. You can even get it from coffee and from solid foods that have a high water content.
Organic vs. GMO
People worry about the sources of their food. They commonly believe that organic is healthy and GMO is unhealthy. The evidence doesn’t support those beliefs. A recent systematic review[xxi] of 240 published studies concluded that “The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods.” It suggested that consumption of organic foods may reduce exposure to pesticide residues and antibiotic-resistant bacteria, but it didn’t show that this reduction had any significant implications for human health. The amounts are tiny, organic farming also uses pesticides, and simply washing produce removes most residues. People also argue that organic tastes better, but blinded taste tests don’t bear that out, and taste probably depends more on freshness than on methods of cultivation. Much of the hype about organic food is based on the “natural is better” fallacy rather than on any actual evidence. Organic food tends to be higher priced, which makes it harder for consumers to buy sufficient nutritious food.
Demonization of GMOs is based on the natural fallacy, on scientific illiteracy, on distrust of large corporations with financial motivations, and on the myth of the evil Frankenstein who tries to play God. As Neil deGrasse Tyson recently tweeted, “Most who fear genetically altered food are unaware that nearly all food has been genetically altered via artificial selection.” No one rejects seedless watermelons or wants to trade their corn on the cob for teosinte. Modern science doesn’t do anything unique or fundamentally different, it only allows us to speed up the process of genetic modification and improve food for human benefit. Genetic modification has been used to increase a plant’s resistance to disease, to improve herbicide and insecticide tolerance so less can be used, and to increase agricultural yields to feed more people. Golden rice was modified to provide vitamin A to third world children with nutritional deficiencies; it has prevented untold cases of blindness and death. GM foods have been extensively studied and no adverse effects on human health have been found. The highly publicized Seralini study that allegedly showed harmful effects in rats was so flawed that it has now been retracted. As with any technology, genetic modification has the potential for harm, either deliberate or through unforeseen consequences. Continued testing and monitoring is warranted; blanket rejection is not.
Fad diets and diet cults appeal to emotion, not to evidence-based reasoning. They give their followers a sense of belonging, a sense of control over their health, and a virtuous feeling of doing something that is difficult but good for them. Decisions come first, rationalizations come later. True believers can always find a few cherry-picked scientific studies that tend to support their beliefs. Confirmation bias allows them to notice any feelings of improvement and give diet the credit.
Those magazines at the grocery checkout stands can be relied on to keep you up to date on the latest fad diets that your favorite celebrities are trying. The variety is astounding; the proof is nonexistent; and the premises are often mindbogglingly silly. An article in the Huffington Post recently listed the “14 worst fad diets you should absolutely never try”:[xxii]
- The Raw Food Diet.It prohibits any food that is cooked or processed in any way, ignoring the fact that cooking can improve access to nutrients. Raw food preparation is onerous, requiring hours of juicing, germinating, sprouting, dehydrating and rehydrating, blending, cutting, chopping, etc. And while it does put a healthy emphasis on fruits and vegetables, most people find the diet unpalatable, inconvenient, and hard to stick to long-term.
- Alkaline Diets. They prohibit meat, dairy, and a lot of other healthy foods, based on the concept that acidic foods are bad for you. The underlying rationale is pseudoscientific and the diet has never been demonstrated to improve health. Misguided devotees monitor their urine pH, failing to understand that nothing in their diet can change their blood pH, which is maintained in a narrow range by homeostatic mechanisms. Changes in urine pH only show that the kidneys are doing their job.
- The Blood Type Diet. Popularized by naturopath Peter D’Adamo, it postulates that people with different blood types need to avoid certain foods. There isn’t a shred of credible evidence either for the rationale or the effectiveness of the recommendations, and the diet restricts a lot of perfectly healthy foods.
- The Werewolf Diet.This requires fasting during full moon or new moon, and eating differently for each phase. (Why? Because werewolves do it? Because of the tides? This may serve as a reminder that the origin of the word “lunacy” derives from moon.) Fasting can produce temporary loss of a few pounds, but the weight will come right back. The myth of the moon’s effect on human physiology is as silly as astrology. And speaking of astrology, there’s also a Zodiac diet.
- The Cookie Diet. 500-600 calories a day of special high-protein, high-fiber cookies plus a normal dinner. A gimmick to limit calorie intake, unnecessarily restrictive and the deprivation during the day may lead to binging at dinner.
- The Five-Bite Diet. You can eat whatever you want, but you must skip breakfast and eat five bites of food for lunch and dinner. Unless you take improbably huge bites, your calorie intake will be limited to unhealthy levels and nutrition will suffer.
- The Master Cleanse/Lemonade Diet. This one buys into the detoxification myth. For several days, dieters subsist on lemon juice, cayenne pepper and maple syrup mixed with water. This is a starvation diet that will indeed drop pounds, but that will cause unpleasant side effects (fatigue, nausea, dizziness, etc.). And you lose muscle instead of losing fat. Skepticpublisher Michael Shermer tried this diet for a week during his cycling days and bonked horribly during long rides. When he returned to a normal diet he got sick from that as well since his body wasn’t used to processing food.
- The Baby Food Diet. This allows up to 14 jars of baby food a day, each containing 20-100 calories, followed by a low calorie dinner. Just another gimmick to decrease total calorie intake, and an embarrassment when others see you carrying around jars of baby food.
- The Cabbage Soup Diet. You prepare a fat-free cabbage soup and eat it three times a day along with a few other low-calorie foods. That much cabbage produces bloating and gas, and the diet is deficient in protein and other nutrients.
- The Grapefruit Diet. This one has been around for 80 years and is based on the myth that grapefruit produces fat-busting enzymes. We know that enzymes in food are destroyed in the stomach and don’t survive to act as enzymes in our bodies. How it really works is that people get so tired of monotonously eating one food item that they eat less. This diet is very low in calories but is not healthy.
- The Sleeping Beauty Diet. If you’re sleeping, you’re not eating. Sedatives will put you to sleep. I don’t think I need to explain why this is not a good idea.
- The HCG Diet. The hormone human chorionic gonadotropin allegedly acts as an appetite suppressant. It must be injected and accompanied by a 500-calorie diet. It has been tested and proven not to work: people lose weight just as well on 500 calories without the injections. To compound the silliness, there is a homeopathic HCG diet using drops that have all the HCG diluted out of them.
- The Tapeworm Diet. Dieters deliberately consume tapeworm eggs so the adult worms will take up residence in their intestines and eat some of the partially digested food, thereby limiting the amount available for humans to absorb, so they tend to lose weight. Tapeworm infections can cause a variety of unpleasant symptoms and can lead to serious complications when masses of them block the intestine or when they migrate to other parts of the body like the liver, heart, eyes, and brain. The yuck factor alone ought to be sufficient to deter most people from following this diet.
- The Cotton Ball Diet. Fiber, anyone? They have to soak the cotton balls in orange juice to get them down. This is dangerous, deprives the body of nutrients, and can lead to intestinal blockages.
This list is incomplete. There are so many more! The “yeast connection” blames a lot of nonspecific symptoms on an alleged overgrowth of yeast in the body that can’t be diagnosed with medical tests and prescribes avoidance of foods that are falsely believed to encourage the growth of yeast. The Maker’s Diet restricts dieters to foods that are mentioned in the Bible. Pastor Rick Warren has developed The Daniel Plan based on a story in the book of Daniel about captive Israelites in Babylon. Nebuchadnezzar allowed Daniel and three other captive Israelites to try a diet of vegetables and water, and at the end of 10 days they appeared healthier than those who dined at the king’s table. Weight loss was not even mentioned, and this is hardly the kind of experimental evidence we can trust. Even if the story is true, the Bible has lower scientific standards than The New England Journal of Medicine and no peer review.
The Gluten-Free Fad
One of the biggest fads today is the gluten-free craze. Celiac disease is a serious autoimmune disease; patients must scrupulously avoid gluten or risk severe symptoms and permanent damage to the cells lining the small bowel. People who have not been diagnosed with celiac disease by a doctor and do not meet the criteria for the disease often believe they must avoid gluten because they are “gluten sensitive” and get symptoms from eating it. A randomized controlled trial showed evidence for the existence of non-celiac gluten sensitivity. But then a better trial showed that it was not gluten these patients were sensitive to, but FODMAPS (fermentable oligo-di-monosaccharides and polyols).[xxiii] Examples of FODMAPS are fructans in foods like wheat, garlic and artichokes; fructose (found in fruits and other foods); lactose in dairy products; and galactans found in some legumes. A low-FODMAP diet has been developed and has been successful in treating irritable bowel syndrome (IBS).
People who have no idea what gluten or celiac mean have jumped on the gluten-free bandwagon because some celebrity is on it and they have the mistaken idea that it will produce weight loss and is a healthier way to eat in general. A cardiologist named William Davis has contributed to the mythology by inventing the Wheat Belly Diet, claiming that the traditional foods relied on by billions of people through the ages, including wheat, rice, corn, and potatoes are unhealthy, cause a big belly, and damage the brain. This is just another low-carb diet that ignores the bulk of the scientific evidence, makes false associations, and exaggerates grains (pun intended) of truth into delusional mountains.
Variations of Vegetarianism
Fruitarians limit themselves to a diet of at least 75% fruits. Some eat only fallen fruit. They are under the illusion that humans evolved to eat only fruit, that we are frugivores rather than carnivores or omnivores. Of course, that is demonstrably untrue. Some of them argue that the human body is unable to digest meat, also demonstrably untrue. A fruit-only diet doesn’t make sense and it leads to nutritional deficiencies, especially in children. Fruitarians can develop protein energy malnutrition, anemia, and low levels of iron, calcium, essential fatty acids, vitamins, and minerals.
Then there are vegetarians and vegans: 10% of Italians and Swedes, 13% of Americans, and 20-42% of Indians self-identify as vegetarians. Vegans avoid animal products entirely, lacto-ovo-vegetarians allow eggs and milk, and some consider themselves vegetarians but occasionally eat small amounts of fish or even meat. Some vegetarians are more concerned about the environment or about animal cruelty than about health, but there is evidence that a vegetarian diet is a healthy one, and it is certainly healthier than the standard American diet. Seventh-Day Adventists are vegetarians; studies show that they live longer and are healthier than non-Adventists, but that could be due to other aspects of their healthy lifestyle. And other studies have suggested that any advantages accruing to vegetarians are likely due to the ample amounts of vegetables in their diet rather than to avoidance of animal products.[xxiv]
Dietary Restriction, Detoxification, and Fasting
The one thing that has been proven to increase longevity in animals is severe calorie restriction (to 40% of the usual intake). Studies in roundworms, flies, fish, mice, and other animals are encouraging; but no human studies have demonstrated increased longevity, and primate studies have had mixed results. Some researchers think that genetics and dietary composition may be more important for longevity than calorie restriction. It is hard to maintain good nutrition with severe calorie restriction, and it is not a diet most people are able to stick to over the long term. In the Minnesota Starvation Experiment,[xxv] a semi-starvation diet led to serious physical and psychological problems.
What about intermittent fasting? It has a long tradition in religions, where it has instrumental in triggering visions and ecstatic states, and where it has been endowed with meanings for self-control, purification, sacrifice, and group cohesion. Intermittent fasting works well to reduce overall calorie intake, as long as dieters don’t compensate by eating more once the fast is over. The daytime fasting/nighttime feasting of Ramadan often results in weight gain.[xxvi]
Fasting is sometimes associated in the modern mind with “detoxification,” as in the pseudo-religious juice cleanse purification rituals. The need for detoxification is a myth; the kidneys and liver do the job quite well, and there is no evidence that colon irrigation, detoxification footbaths, or any other detoxification methods actually remove any toxins or improve health in any way. There are hints that fasting might benefit certain diseases, but it might also lead to inadequate nutrition and compromise the immune system.
Some cancer patients have given up sugar because of the misguided idea that cancers feed on sugar. This myth is based on a misunderstanding of Otto Warburg’s 1924 study of cancer metabolism; restricting sugar in the diet has no effect on cancer outcomes.
Some diet advisers not only want to tell you what to eat, but how to eat. Certain foods shouldn’t be mixed, they claim; food should be eaten in a certain order; you should avoid drinking liquids with meals. Advocates of Fletcherizing even want to tell you how to chew. Fletcher said each mouthful of food must be chewed 32 times. His slogan was “Nature will castigate those who don’t masticate.”
The diet supplement industry is big business that capitalizes on irrational fears. Some people argue that the nutritional content of our produce is diminishing over time. There may be a grain of truth to the claim, but as Steven Novella says, “It’s complicated” and the practical importance is negligible.[xxvii] People take multivitamins as psychotherapy, to assuage worries that they are not eating a good enough diet.
Although some people need dietary supplements for medical reasons (for instance folic acid to prevent birth defects or iron supplements for iron deficiency anemia), recent research has questioned the wisdom of vitamin supplementation for the general population. Every vitamin can be toxic in large amounts, and studies have found harmful effects from antioxidant supplements and even for the time-honored daily multivitamin. More and more studies are finding a link between both individual vitamins and daily multivitamins and adverse health effects. Vitamin E supplements and high levels of omega-3 are associated with an increased risk of prostate cancer; multivitamins, iron, and copper are associated with a higher rate of death in postmenopausal women; antioxidants like vitamin A, E, and beta-carotene may increase mortality;[xxviii] a large study in Sweden found that vitamin supplements did not improve mortality;[xxix] smokers who take beta carotene are more likely to die of lung cancer; etc. The body processes vitamins differently depending on whether they are ingested alone in large amounts or combined with other nutrients in food. It makes far more sense to eat a more nutritious diet than to continue with an inadequate diet and try to compensate with supplement pills.
Bodybuilders and other athletes tend to overdo the supplements and protein shakes because they have been misled about their requirements. Science tells us there is no advantage to eating more than the 1.2g per kg of body weight that the typical American diet provides.[xxx]Once the muscles have become developed, protein requirements drop, and overdoing the protein counteracts natural adaption so that a body builder might tend to lose muscle weight if he stops chugging the protein shakes that he didn’t really need in the first place.
What Should we Eat?
The typical American diet is not a very healthy one. It includes too much meat, too many processed foods, too many calories, too few fruits and vegetables, too many empty calories from sugar and high fructose corn syrup that have no other nutritional value, and too much fast food. Much has been written about the evils of big corporations and mass production. Our crops are becoming monocultures and losing genetic variety. The practice of feeding antibiotics to livestock promotes the development of antibiotic resistant strains of bacteria. Feedlots and battery cages are cruel to cows and chickens. Industry has been blamed for manipulating the food choices of the whole population in an unhealthy direction for its own profit. Restaurants are blamed for excess salt, large portion sizes, and a paucity of healthier, low calorie options. Fast food is blamed for its corrupting influences. There are certainly downsides to industrialized food, but we mustn’t lose sight of the many benefits. Mass production has made more food, safer food, and food of more consistent quality available to more people at lower prices. We can look for ways to correct the bad practices of big corporations without throwing out the baby with the bath water.
People have tried to blame all our modern health problems on poor eating habits. Gluten, yeast, acid foods, and other components of a healthy diet have served as handy scapegoats. There’s a plethora of diets but a paucity of proof. People who follow fad diets are convinced that they work. They are satisfied that they are getting the results they want, but they don’t stop to wonder whether other diets might work just as well to get those same results. Since humans can thrive on a variety of diets, it’s easy to become convinced that whatever you are eating is the healthiest choice.
In the future, science-based nutritionists may be able to provide individual diet advice tailored to each person’s specific genetic makeup, but we’re not there yet. Several companies offer direct-to-consumer genome tests; some of them advise customers about the best diet for their genes and conveniently sell them dietary supplements. They promise more than they can deliver; they are not much better than the “individualized” diets based on ABO blood groups or horoscopes. Individual differences are likely to be small; basic nutrition depends on physiology and is the same for every member of the species.
So what’s the answer to the question of what we should eat? The answer is that there is no answer. As Matt Fitzgerald says,[xxxi]
Science has not identified the healthiest way to eat. In fact, it has come as close as possible (because you can’t prove a negative) to confirming that there is no such thing as the healthiest diet. To the contrary, science has established quite definitively that humans are able to thrive equally well on a variety of diets. Adaptability is the hallmark of man as eater. For us, many diets are good while none is perfect.
Until better evidence is available, I think the best plan is to adopt the diet advice that most nutrition experts are able to agree on and that is epitomized by Michael Pollan’s pithy “Eat food. Not too much. Mostly plants.” More fruits and vegetables, less red meat, less processed food, more variety, limit the calories, control your weight.
In his book Diet Cults,[xxxii] Matt Fitzgerald lists a hierarchy of 10 food categories from more healthy to less healthy:
- Nuts, seeds and healthy oils
- High quality meat and seafood
- Whole grains
- Refined grains
- Low quality meat and seafood
- Fried foods
He recommends eating foods in amounts that correspond to their place on the hierarchy with the major emphasis on vegetables and fruits. Foods that are lower on the list need not be avoided, but the amounts should decrease as you go down the list. One could argue with his list, and it hasn’t been established that his plan will keep people healthier or make them live longer, but it is as good a place as any to start, and it is consistent with the limited evidence that we do have about nutrition.
Finally, remember that health and longevity are not the only reasons we eat. Think about eating to make you happy, not just eating to make you healthy. Eating is one of the great pleasures of life. Is it worth gambling on uncertain diet advice if it means you have to forgo the pleasures of your favorite foods and of shared dining experiences? There’s an old joke where a doctor tells an elderly patient he will live longer if he stops smoking, drinking, eating unhealthy foods, and having sex; the old guy replies, “You call that living?!”
[xi]Fitzgerald, Matt. 2014. Diet Cults: The Surprising Fallacy at the Core of Nutrition Fads and a Guide to Healthy Eating for the Rest of Us. Pegasus Books.
[xiv]Taubes, Gary. 2008. Good Calories, Bad Calories. Anchor.
[xvi]Campbell, T. Colin, and Thomas M. Campbell. 2006. The China Study: The Most Comprehensive Study of Nutrition Ever Conducted and the Startling Implications for Diet, Weight Loss, and Long-term Health. BenBella Books.
[xxxi]Fitzgerald, op cit., 10
[xxxii]Fitzgerald, op cit, 260-61
This article was originally published in Skeptic magazine.