Diet sodas make you fat? I'm not buying it.

It's an extraordinary claim, which therefore requires extraordinary proof. But that isn't stopping popular websites like Cracked from trotting it out for its shock value. The claim: that drinking diet soda can actually make you fatter.

Before we get to the studies, let's step back and examine the insulin cycle, using a series of grossly generalized statements: When you eat something sweet, your pancreas pumps out insulin. Insulin causes your body to take all the calories floating around in your bloodstream and lock them up as fat (instead of burning them). It also makes you hungrier so that you eat more. Truly a vicious cycle.

The claim is that your body is stupid, and artificial sweeteners kick off this insulin cycle just like regular sweeteners. Hypothetical sweetness sensors in your mouth and throat flag the Diet Coke as being "sweet," and signal your pancreas to start creating insulin.

The first study was performed in Hungary. They took two identical groups of rats and fed them rat chow. One group had water which contained artificial sweetener. The other group had plain water. At the end of the study, the rats on sweetener weighed more, although both groups had consumed the same amount of rat chow.

If artificial sweetener was kicking off the insulin cycle, wouldn't we expect to see those rats eating more?

The second study comes from Perdue University. Rats fed artificially sweetened yogurt gained more weight than rats fed yogurt which had been sweetened with glucose. This, too, goes against everything we know about the insulin cycle. If the claims about artificial sweetener were true, then both groups of rats should have gained weight. (What this study needed was a control group fed unsweetened yogurt.)

I'm not dismissing the idea out of hand. But it's going to take better studies to convince me. Not least because the sugar and corn industries have a huge stake in convincing people that artificial sweeteners are worse for you than real sugar or corn syrup. Any time that much money is involved, you want to be extra-skeptical of any study results. (It's enough to make me want to buy some rats and do my own tests!)

Image courtesy Flickr/niallkennedy