What to Eat: Food. Not Too Much. Mostly Plants.

As I was feeding the dog, it occurred to me that dogs have a very straightforward relationship with food. Our Labrador’s philosophy seems to be “eat everything you can get and as much of it as possible, whether it’s food, ice cubes, pine cones, wood, or anything else you can chew or swallow.” In two of his more memorable exploits, he ate the head off an ornamental wooden duck and swallowed a Kleenex-wrapped razor blade (requiring major surgery).

Humans have a complex, conflicted, troubled relationship with food. Refueling our bodies generates anxiety, guilt, and irrational behaviors. We follow kosher, halal, or other religious dietary guidelines. We worry about omega-3s, antioxidants, and trans-fats. We berate ourselves for accepting that tempting slice of chocolate cake.

It was not always thus. In less affluent times, humans were mainly concerned with whether they could get enough food (of any kind) to survive. When food was plentiful, they ate a lot because they might not get enough later. They followed tradition and ate whatever was customary in their culture. Then modern science came along and complicated things.

James Lind started it. He was the British doctor who discovered that citrus fruits prevented scurvy on long sea voyages. That led to the discovery of vitamin C and indirectly to the discovery of other vitamins and nutrients and the obsession with getting enough of all the right components.

When I was growing up, we knew more about vitamins and nutrition than our ancestors did, but life was still fairly simple: Mom’s idea of dinner was a meat, a starch, a green vegetable, a yellow vegetable, maybe fruit but more likely a piece of cake or pie for dessert, and whole milk to drink.

Mom wasn’t worried about us getting fat. She made us eat everything on our plates because children were starving in Africa(!?).  It didn’t matter if you were full or if you retched every time you tasted a lima bean; you had to sit there until every morsel was gone. We didn’t even have a dog to slip the offending bits to. Nevertheless, we were never overweight.

Today life is much more complicated. We eat pre-prepared convenience foods, we eat out, we eat fast foods, we snack, we eat in the car. Our grocery stores are replete with labels telling us more about our food than any rational person would want to know. We have a surfeit of choices: low-fat, non-fat, diet, low-sodium, low-cholesterol, fortified, organic… We have to make way too many decisions.

Science has learned a lot about nutrition, but the knowledge tends to get garbled before it reaches the average consumer. My husband overheard a woman in the grocery store asking her companion if they should buy the cucumbers – they weren’t sure they were organic. My ever-helpful husband informed them that all cucumbers are organic (as opposed to inorganic things like salt and thumbtacks). The woman retorted, “But how can I be sure they don’t have fish genes?!”

She probably would have been shocked to learn that ALL cucumbers have fish genes.  All fish have cucumber genes, too. All living organisms share some of the same genes. I wonder if this woman had any idea what “organic” really meant, either in the original sense or in the new sense of foods grown without conventional pesticides and artificial fertilizers. I wonder if she thought a fish gene in a cucumber could hurt her – make her grow fins, maybe?

“Organic” has become a meaningless buzzword; I flinch when I see it on a label: it inclines me not to buy that product. What we really want is sustainable agriculture that does minimal damage to the environment and produces food that is nutritious, tastes good, and has no unnecessary contaminants.  “Organic” food as currently defined doesn’t necessarily achieve those goals. Produce may have been trucked long distances using up fossil fuels and making it less fresh than local produce; it may cost more and not look as pretty. It may not use land efficiently. Absent pesticides, plants may produce higher levels of natural pesticides for self-defense – could that be bad for us? Sometimes locally grown foods that are not technically “organic” are a better choice. We should ask questions rather than reflexively buy “organic.”

The anxiety and stress generated by food ideology may do as much harm as eating a less healthy diet. Food is not just fuel, it’s also a social experience, it carries all kinds of connotations, and it’s one of the major pleasures of life. Dean Edell thinks we should stop worrying and just “Eat, Drink, and Be Merry” (he wrote a book with that title).

Michael Pollan, author of The Omnivore’s Dilemma, has written a new book entitled In Defense of Food: An Eater’s Manifesto. I question some of his details, but I wholeheartedly agree with his main message: “Eat food. Not too much. Mostly plants.”

He argues that “Thirty years of nutritional advice [particularly the advice to replace fats with carbohydrates] have left us fatter, sicker, and more poorly nourished.” We’d be better off eating “real” (not processed) foods, limiting calories to avoid obesity, and doing what almost all dietitians and mothers tell us to do anyway: eat our vegetables. I’d only add one thing to that: eat a variety of different foods to minimize the chance of missing some trace nutrient.

Nutrition science has spawned the ideology of “nutritionism,” viewing food as simply the sum of known nutritional components. We’d like to believe “that experimental science has produced rules of nutrition which will prevent illness and encourage longevity.” Don’t be so sure.

We do know enough to support patients whose digestive tract is kaput by feeding them intravenously. TPN (Total Parenteral Nutrition) provides all the known necessary nutrients in the proper amounts (salts, glucose, amino acids, lipids, and vitamins).  It can extend lives but can cause complications. It’s also inconvenient, no fun, and probably can’t maintain optimal health for very long. We just don’t know enough yet.

Foods are very complex. Pollan gives the example of thyme: it contains alanine, anethol essential oil, apigenin, ascorbic acid, beta-carotene, caffeic acid, camphene, carvacrol, chlorogenic acid, chrysoeriol, derulic acid, eriodictyol, eugenol, 4-terpinal, gallic acid, gamma-terpinene, isichlorogenic acid, isoeugenol, isothymonin, kaemferol, labiatic acid, lauric acid, linalyl acetate, luteolin, methionine, myrcene, myristic acid, naringenin, rosmarinic acid, selenium, tannin, thymol, tryptophan, ursolic acid, and vanillic acid.

We don’t know how each of these affects the body, either singly or in combination. Could they turn on the expression of some gene? Could they interact with chemicals in another food to cause harm or good?

Science can’t possibly test every chemical substance in every food, much less test them in combination. Science can’t claim to have identified every nutrient important to health. Science can’t even do a good job of testing the effects of different diets, because you simply can’t do a properly controlled long-term diet experiment on humans. You can’t divide people into 2 groups and make them eat exactly what you want. You can’t rely on their self-reports of what they eat: people lie, over- and under-estimate, cheat, forget.

Science changes its provisional conclusions when new evidence becomes available; that’s the strength of science, but it’s aggravating. Yesterday coffee was bad; today it’s good. First scientists said we should avoid cholesterol. Then they said to avoid saturated fats. Then they decided neither of those was really so bad; it was trans-fats we needed to avoid. We’re still refining our knowledge.

People with high LDL cholesterol levels are advised to eat a low-fat diet, but it may only lower lipid levels by 3-6%, which may not make much practical difference in the long run. What if you’re 80 and have high cholesterol? Should you follow a strict diet and spend your remaining years denying yourself all the foods you love? Should you eat what you like and take statins, which lower cholesterol much more effectively and have other heart-protective effects? Should you even worry about your cholesterol in the first place? The answers are not black and white. Remember the old joke where the doctor tells the patient he’ll live to be 100 if he avoids alcohol and sex and the patient says, “You call that living?”

Some people with good genes can probably eat a high-fat diet with impunity, like the Maasai (who mix blood and milk) and the Inuit (who eat raw meat and blubber). We are reasonably certain that humans can get all the necessary nutrients (even vitamin C) from a diet of nothing but raw meat. (Don’t try this at home.) Pollan says, “The human animal is adapted to, and apparently can thrive on, an extraordinary range of different diets, but the Western diet… does not seem to be one of them.”

Incidentally, our DNA still has the gene to make vitamin C; it’s just turned off. Maybe genetic engineers can turn it back on some day. Vitamins could conceivably become obsolete.

Pollan tells us to be the kind of person who takes supplements. Don’t actually take supplements, just be the kind of person who does (i.e., health conscious). Learn about nutrition, but don’t be its slave. Make reasonable choices: if two foods are equally appealing, you can choose the one with fewer calories, less fat, more vitamins, or that was grown locally. If you really like an “unhealthy” food, treat yourself and enjoy it occasionally. If you dislike a “healthy” food, don’t feel obligated to eat it.

Eat a variety of foods. Not too much. Mostly plants. Bon appétit!

This article was originally published as a SkepDoc column in Skeptic magazine.




Dr. Hall is a contributing editor to both Skeptic magazine and the Skeptical Inquirer. She is a weekly contributor to the Science-Based Medicine blog and is one of its editors. She has also contributed to Quackwatch and to a number of other respected journals and publications. She is the author of Women Aren’t Supposed to Fly: The Memoirs of a Female Flight Surgeon and co-author of the textbook, Consumer Health: A Guide to Intelligent Decisions.