130501_SUG_ColaDrinkSoft drink scolds — the kind of people who back the Center for Science in the Public Interest’s (CSPI) call for soda Prohibition or Kelly “Big Brother” Brownell’s plan to tax soda more than beer — have a problem with zero-calorie drinks. It’s hard to blame a product for causing obesity, as the scolds have to do in order to follow their misguided playbook, if four of the top ten such products have no calories.

The activists’ response has been to attack those beverages too. CSPI lists the product used to sweeten most of them — aspartame — in its “avoid” category despite repeated findings by international agencies that it is safe (except for a small number of people with a genetic condition called phenylketonuria who can’t metabolize it).

Now, an opinion piece in a medical journal is getting wide coverage for suggesting that zero-calorie soda makes you just as fat as the full-sugared stuff. Supposedly, zero-calorie sweeteners make the body’s response to foods go haywire.

So, what’s the evidence for this latest round of stories? There really isn’t any — it is driven by an opinion piece in a medical journal. A recent controlled trial found that consuming artificially sweetened beverages reduced children’s body mass indexes compared to a group consuming full-calorie beverages, and a separate clinical experiment found that artificially sweetened beverages could assist weight loss.

Statistical associations like those the opinion author cites between overweight status and diet soft drink consumption could in fact be an example of reverse-causation: People trying to lose weight might be switching to the zero-calorie beverages to reduce their calorie intake. In the end, the only proven way to lose weight for the long term is to use more calories than you consume, and when you consume diet soft drinks you aren’t consuming many at all.