This story appears in the September 2017 issue of National Geographic magazine.
If only it were as simple as “An apple a day keeps the doctor away.” Nutrition scientists are in fact constantly scrutinizing the health properties of foods. Everything in this picture, along with olive oil and tea, has been the subject of more than 20 studies in the past 25 years, says physician Michael Roizen, chief wellness officer at the Cleveland Clinic. Why? “They either have unexpected benefits,” he says, “or are commonly consumed but may have risks.”
Some foods—like pomegranates and pistachios in the U.S.—rise to nutrition fame because a large company that dominates the production and sales pays for much of the research. But sponsored studies can shade the science, says Roizen. The National Dairy Council, for instance, “has a huge marketing arm,” allowing it to widely promote the genuinely nutritious aspects of milk, yogurt, cheese, and more. Some dairy products contain a compound called lecithin, long considered healthy. However, it interacts with gut bacteria to produce the damaging compound trimethylamine, which causes inflammation and can lead to disease. Egg yolks also have lecithin in them, so Roizen advises minimal intake.
Highly studied foods are not always the ones you should eat. Roizen suggests avoiding low-carb diets that emphasize butter, cheese, and lots of meat. Even healthy-sounding grass-fed beef contains carnitine, another trimethylamine producer. “The protein is not different whether it’s grass-fed or grain-fed.” Red wine or a generous splash of unadulterated extra-virgin olive oil—two top-studied foods—can slightly mitigate the negative effects of meat and dairy. But alcohol is hazardous, and olive oil is high in calories.
The best bet, says Roizen, is to follow science, not sensation. Eat vegetables. Instead of meat, choose salmon or ocean trout—they have more good fish oil than most other high-fat, low-mercury species. Drink black coffee (it can be good for the liver). Snack on nuts, but not too many. And for dessert: a bite of dark chocolate.