When should you be skeptical? Any time you see a report that a single food, beverage, supplement, food product, or ingredient causes or reduces the risk for obesity, heart disease, type 2 diabetes, or cancer, it is a good idea to envision a red warning flag flying high in the air. The studies may have identified associations between the food factor and the disease, but associations can be due to any number of other causes. Dietary patterns, not single factors, are what matter to health. Look out for words like “miracle” or “breakthrough.” Science tends to proceed in small increments and rarely works that way. And please be especially skeptical of “everything you thought you knew about nutrition is wrong.” Science does not work that way, either. Whenever you see “may” or “might”—as in “may reduce the risk of heart disease” or “might improve cognition in the elderly”—recognize that these also mean “may not” or “might not.” Overall, it is always a good idea to ask whether study results seem plausible in the light of everything else you know. As an eater, you should be wary of media hype about whether fat or sugar is a more important cause of health problems. This question ignores basic principles of nutrition: we eat foods, not nutrients, and how much we eat is often just as important as what we eat. Diets of enormous variety, from Asian diets traditionally based on rice (carbohydrates that convert to sugar in the body) to Mediterranean diets rich in olive oil (fat), can all promote long and healthy lives. The basic principles of eating healthfully have remained remarkably constant over the years: eat a wide variety of relatively unprocessed foods in reasonable amounts. Note that these same dietary principles apply to prevention of the entire range of diet-related chronic diseases. If an industry-funded study claims miraculous benefits from the sponsor’s products, think, “Advertising.
Marion Nestle (Unsavory Truth: How Food Companies Skew the Science of What We Eat)