We've all heard the standard dogmas: whole wheat bread is good, white bread is bad; spinach is good, pork is bad; saturated fats are bad, unsaturated fats are good.. And we’ve been told hundreds of times to load up on various vitamins and supplements. You can't keep them straight. One year it's vitamin E that will make you smarter and the next year its vitamin A. At least the food police are consistent on a few things; for example, they all love omega-3 fatty acids.
Most reasonable people have learned to be skeptical about nutritional claims. We've been through several cycles of wine being good for you, then bad for you, and good for you again. We've listened to so many claims about the wonders of this diet or that one that we've given up trying to make sense of it all. About the only thing we agree on is that the diet kooks are probably wrong in spite of the fact that Larry King and Oprah Winfrey believe in them.
Who is to blame for all this mess? Is nutrition science really a science or is the field really in as much trouble as it seems from the outside? Is the media to blame for misrepresenting the science?
Reynold Specter is a clinical professor of medicine whose areas of expertise include vitamins and the effect of diet on kidney functions. He discusses the problem in the May/June issue of Skeptical Inquirer: Science and Pseudoscience in Adult Nutrition Research and Practice.
Here’s the take-home message ....
Human nutrition research and practice is plagued by pseudoscience and unsupported opinions. A scientific analysis separates reliable nutrition facts from nutritional pseudoscience and false opinion.According to Specter, most nutrition claims are based on bad science. Many of them are unproven and a surprising number have actually been disproven by well-controlled, double-blind clinical studies.
So, what do we know for certain? We know that the average adult needs vitamins, essential amino acids, essential fatty acids, high quality protein (animal or vegetable), minerals, and a source of fuel calories. The fuel can come from carbohydrates, fat, or protein or some combination of these.
We know that carbohydrates, fats, and proteins can be inter-converted once they have been digested. We know that the levels of most metabolites are maintained at steady state levels (homeostasis) in healthy adults. And finally, we know that nutritional requirements change as you get older.
Just about everything else is either wrong or debatable according to Reynold Specter. The majority of people are neither too fat nor too thin. They have a body mass index (BMI) less than 30—usually in the optimal range of 20 to 25. For normal healthy people we can ask whether food supplements are necessary and whether there are particular supplements that will prevent disease.
The answer, notwithstanding thousands of positive EOS [epidemiology observation studies] and, in some cases, small inadequate clinical trials is there is no rigorous scientific evidence for the utility of dietary supplements, including megavitamins in normal weight (nonpregnant) adults with a stable BMI of 20 to 25 eating a diet containing adequate amounts of nutrients in Table 1.Specter says that many common claims have been shown to be false by scientific studies. They include claims that fibre will prevent bowel cancer, that megadoses of vitamin D will prevent dementia, and that a low-fat diet will reduce your risk of a heart attack
Why then, have so many papers been published in the medical literature claiming benefits for food supplements and certain diets? Part of the problem is that these preliminary studies are just that—they were never intended to be the last word on the subject. Part of the problem is what's called “healthy person bias." Health conscious people tend to exercise and take supplements. This group is going to have fewer medical problems regardless of whether they take supplements or not but small scale studies don't control for that so it looks like there's a causal relationship between taking supplements and good health.
But most of the problem is due to how the system works. There are too many people who benefit from the status quo in nutritional science and hardly anyone who benefits if the quality of publications were to be improved.
Under the current system, authors find it easy to publish preliminary work; journal editors are happy to make larger profits; commercial enterprises enjoy increases in the sales of food supplementals and fad diets; and the news media have lots to write about. Don't expect this to change in favor of good science.
The bottom line is that the food supplement industry is dominated by poor science at best and outright quackery at worst. One could argue that this situation is harmless. After all, if P.T. Barnum's favorite group1 of people want to waste their money, then why should the rest of us care? Reynold Specter tells us why our society needs to be concerned.
As I noted earlier, even widely used supplements such as vitamins E, C, and carotene in ‘standard megadoses’ (greater than five times the RDA) may indeed be harmful. The potential for harm for many other types of supplements is not been systematically studied, although there are convincing data that certain supplements may damage the liver, kidney, or heart or alter drug metabolism. For example, the amino acid tryptophan (used to induce sleep) and ephedrine-containing herbs (for asthma) were removed from the over-the-counter market because of severe toxicity, including deaths in some people.What about diets? There is no scientific evidence to support the claims that certain common foods are better than others. For the average person, saturated fats are no better or worse than unsaturated fats and potatoes or white rice aren't any worse for you than whole-wheat. And there's nothing magical about eating five daily servings of fruit and vegetables. Everything works as long as you don't eat too much.
If you are obese you need to eat more moderately in order to cut back on fuel intake. Everybody knows this. It is not rocket science. But do weight loss diets actually work?
None work well. On average, over the long term, obese humans do not lose much weight on voluntary low-calorie diets of any kind. (There are of course a few obese individuals who have ‘self discipline’ and can lose weight and keep the weight off. Their secret is obscure.)Many people profit from weight loss diets but unfortunately the patients aren't among them.
Be skeptical of the claims of so-called nutritionists. Don't be fooled into thinking that "nutrition science" is any more scientific than creation science.
1. I know it was really David Hannum, and not P.T. Barnum, who said "There's a sucker born every minute."