New research may finally explain how zero-calorie sweeteners could cause you to gain weight.
People who use artificial sweeteners are more likely to be overweight. Of course, that doesn't prove that zero-calorie sweeteners cause you to gain weight. It's just as likely--actually, more likely--that people who are overweight are more likely to choose diet soda and other artificially sweetened foods in an effort to cut calories.
Nonetheless, there's been a lingering suspicion that even though using artificial sweeteners instead of sugar can save you some calories, they might somehow trick your body into gaining weight anyway. One theory was that the body might respond to the sweet taste by releasing fat-storage hormones--however, studies failed to confirm this hypothesis.
But a new study suggests a tantalizing new explanation: although they don't directly raise your blood sugar, artificial sweeteners may affect how your body responds to the sugars in other foods, leading to elevated blood sugar and, possibly, insulin resistance, weight gain, or even Type 2 diabetes. The key turns out to be in the trillions of microbes that populate your gut.
See also: What is Gut Microbiota?
It's Not Me, It's My Bacteria!
The first key piece of evidence was that people who are overweight tend to have different intestinal flora than normal-weight individuals. Further, it appears that these microbes actually play a big role in promoting obesity. When intestinal bacteria are transplanted from the guts of obese subjects into the guts of normal subjects, the normal subjects start gaining weight. And vice versa.
This alone is a staggering piece of news. Have you ever known someone who ate very little but remained overweight, or someone who could eat whatever they want and not gain a pound? For decades, we've chalked this up to differences in metabolism or physical activity. Sometimes, we even suspect that overweight people are simply eating more than they're admitting to. But a lot of this could actually be due to differences in their intestinal bacteria.