Have you ever wondered why nutrition experts so often change their minds about what constitutes a healthy diet? In the last six months, a variety of experts and nutrition organizations have issued at least as many major dietary guidelines proclaiming the next set of instructions on what to eat to prevent cancer, whether processed foods are really food, whether the type of fat you eat has any effect on developing heart disease, and how to control diabetes with diet. And the next set of U.S. Department of Agriculture (USDA) and Health and Human Services (HHS) dietary guidelines, due out next year, are already creating a buzz.
These new guidelines have, like most dietary guidelines in the past, done little to solidify our understanding of the cause and effect relationship between diet and disease. Even worse, they’re likely to discredit nutritional science. Moreover, guidelines like these tend to suggest, without proper research as proof, that people have control over whether or not they develop certain diseases, and it is therefore their fault if they become ill.
A large part of the issue comes down to funding, and a lack of resources to do the kinds of studies that would help answer some of our most pressing questions. Our insistence on making recommendations — without having the proper research to back them up — has unintended, harmful effects.
Nutrition research, like all medical research, is extremely difficult and expensive. But nutrition research is even more complex than research in other areas of medicine. First, many well-designed studies have failed simply because the subjects couldn’t adhere to the diet: asking subjects to eat a diet lower in salt, for example, can initially make food seem tasteless.
Second, changes in diets have the potential to change dozens of other variables at the same time. When trying to determine whether a low-protein diet decreases cancer, for example, a study may involve reductions in grilled or processed meat — which may contain cancer-causing substances. To control for these coincidental effects, and subtle differences between the subjects, studies of dietary changes often require tens of thousands of participants.