Will Diet Soda Help You Lose Weight?

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Artificial sweeteners have seen decades of controversy, but that controversy has mostly been around whether or not they cause cancer. Early studies showed that saccharin and a mostly abandoned sweetener called cyclamate caused cancer in lab rats. Later studies, however, didn't find any evidence that saccharin, cyclamate, nor any other FDA-approved sweeteners cause cancer in humans. The FDA has since declared at least eight different artificial sweeteners safe for human consumption.

But even while the public was worrying about cancer, some researchers began suspecting that sweeteners had a strange effect on weight. As far back as the 1970s, studies were starting to show that they weren't the magic weight-loss bullet that you might think. This 2017 meta-analysis in the Canadian Medical Association Journal is just one more piece of evidence on an ever-growing pile showing that just because artificial sweeteners don't contain calories doesn't mean that they help you lose weight.

A meta-analysis is a kind of super-charged scientific study that crunches the data from many published papers in one big group to get a result that's more airtight than any one paper on its own. That's what this study did: the researchers found nearly 12,000 papers that focused on artificial sweeteners like aspartame, sucralose, and stevia, and selected a handful that met their criteria. Seven were randomized controlled trials, the kind of experiments that break volunteers into groups: one group gets the test substance, the other group gets a control substance. Thirty were prospective cohort studies, a less rigorous but still-useful kind of study in which researchers collect data from a group of people over a period of time.

What did they find? In the trials, sweeteners had no effect on weight. In the cohort studies, they were linked to a slight increase in weight. The researchers concluded that the use of artificial sweeteners does not help with weight management.

Why? In the cohort studies, researchers didn't control subjects' diets, so it's possible that they rewarded their "good" decisions to choose artificial sweeteners by eating more sweets overall. But in the randomized controlled trials, all groups should have eaten the exact same things, so that doesn't explain it. Some scientists theorize that artificial sweeteners take a toll on weight by affecting changing your gut microbiome and affecting how your body handles glucose. We still don't know for sure, but if you're watching your waistline, it might be good to stick with water.

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