Dear Science,

I have at least a few friends who, as part of trying to lose weight, drink diet soda constantly. Even after a few of them shifted from corn-syrup-packed regular soda to diet, their weight doesn't seem to budge. In fact, the fattest people I know happen to be the biggest diet soda drinkers. I think it's connected, drinking diet soda and being fat. Back me up, Science! Does drinking diet soda make you fat?

Correlating Coke Hater

You're on to something: At least a few studies—including some recent data presented at a scientific conference on diabetes—seem to connect diet soda consumption with metabolic syndrome (the combo of high blood pressure, high blood sugar, obesity, and generally a higher risk for everything you don't want).

One of the first really solid hints of this connection came from a carefully done bit of research by University of Minnesota scientists, published in 2008 in the journal Circulation. This prospective study (which carefully followed a group of people over decades, checking in every three years) used a questionnaire about dietary habits to connect specific foods with the development of metabolic syndrome. As most of us would expect (and probably already know), people who ate a lot of meat and fried foods were much more likely to develop the syndrome. Intriguingly, drinking diet soda was about as associated with developing metabolic syndrome as eating fatty foods and mounds of meat. In contrast, the consumption of sugary drinks (sweetened by corn syrup or cane sugar) was not associated either way. (Consuming dairy was beneficial, protecting against metabolic syndrome.)

The more recent work—from a group at the University of Texas, San Antonio—was an eight-year prospective study attempting to connect the consumption of certain foods with the development of diabetes. The results were similar, with the consumption of soft drinks strongly associated with the eventual development of diabetes. Fascinatingly, almost all of this increased risk came from those who drank diet soft drinks—not corn-syrup- or cane-sugar-sweetened ones. The risk wasn't tiny: The study found a 41 percent increase of being overweight for each can of diet soft drink consumed (on average) per day.

Why would diet soft drinks—which provide no calories—be more likely to cause metabolic syndrome (aka an unhealthy obese person) than sugar-sweetened soft drinks? (To be clear here, sugary soft drinks are no health food. It's just that diet soft drinks are nearly twice as risky for diabetes.) Nobody quite knows yet, but the speculation is interesting. Perhaps artificial sweeteners make us less sensitive to real sweetness—and thus we eat more. Or perhaps the artificial sweeteners trigger our bodies to release insulin, causing our blood sugar to drop, which makes us crave bigger meals later. The eventual answer is going to be enthralling.

Sweetly Yours,

Science

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