Be skeptical of food studies

Pomegranates are high in antioxidants according to a sponsored study - but then again so are most fruits.
Pomegranates are high in antioxidants according to a sponsored study - but then again so are most fruits.Rafiq Maqbool/AP


Q: You were quoted saying that you didn't believe newspaper reports linking diet sodas to an increased risk of stroke and heart disease. How do you decide whether research is good or bad?

A: This one was easy. I didn't think it made sense. Mind you, I'm no fan of diet sodas. They violate my rule never to eat anything artificial. And I don't like the taste of artificial sweeteners.

Whenever a study comes out claiming harm - or benefits - from eating a single food or ingredient, I get skeptical. That's why I also questioned these recent study results: high-fructose corn syrup (HFCS) makes rats gain weight faster than sucrose (table sugar); zinc supplements prevent symptoms of the common cold; and pomegranate juice has greater health benefits than any other kind of fruit.




Mostly, I can't think of a biological reason why diet sodas might lead to cardiovascular disease unless they are an indicator for some other stroke risk factor such as obesity, high blood pressure or binge drinking. It would take a study designed to test this idea specifically - and a good biological explanation - to convince me that diet sodas cause strokes.

The plausibility issue also rises in the HFCS study. Again, I'm not a fan of HFCS - we would all be healthier if we ate less sugar - but from a biochemical standpoint, HFCS and table sugar are pretty much the same. They have similar amounts of glucose and fructose, are digested as quickly and are metabolized the same way. Even the average amounts consumed are about the same. That soda companies are replacing HFCS with sucrose is strictly about marketing, not health.

Controls: The zinc-and-colds study was a comprehensive review (a "meta-analysis") of previous studies done since the first one in 1984. Eleven studies have showed some benefit; seven have not. All of them were placebo controlled, double-blind. This meant that half the participants were given a dummy pill, and neither participants nor investigators were supposed to know who was taking what.




If the studies were not really blinded, the zinc results are questionable. I have no doubt that many people feel better when they take zinc supplements, but I'm not sure whether that's because of something zinc really does or just its placebo effect.



Nutrition research is hard to do, which makes study design and interpretation particularly challenging. Nutrition is a thinking person's field, requiring careful analysis at every step. When you hear a result that sounds too good to be true, it usually is.