A lot of popular food and nutrition writers have taken it as given that diet drinks cause obesity and diabetes, because they somehow trick your body into craving more sweets or calories. Recently this came up again in a article in the Huffington Post by Klein and Melnick.
And honestly it sounds kind of reasonable, but if you go and read the papers, you will see it isn’t really that simple.
This first came up in a couple of papers by Fowler and coworkers who analyzed existing data from the San Antonio Heart study retrospectively and found that people who drank diet sodas did indeed seem to have more weight gain. We reported on these papers here in 2011. In an interview for WebMD, Fowler herself agreed that her studies only provided a correlation between weight gain and diet sodas. They did not prove causation. It could be just as likely that people prone to weight gain were preferentially choosing diet drinks rather than the other way around.
A paper by Clavel-Chappelon and Faherazzi (also summarized here in a press release) studied artificially (ASB) and sugar-sweetened beverages (SSB) and concluded that both groups were at increased risk for Type 2 diabetes (T2D). Again, however, they did not establish causation. They did note in their paper
We cannot rule out that factors other than ASB consumption that we did not control for are responsible for the association with diabetes, and randomized trials are required to prove a causal link between ASB consumption and T2D.
Well then, are there any randomized trials we can look at instead? Actually, there are.
In a 2009 study by Chen, Appel and others, 810 adults were monitored for 18 months with careful recording of their beverage intake. Intake of sugar sweetened beverages was correlated with weight gain, and there was no significant weight gain from artificially sweetened beverages. Let’s repeat: in a randomized study, diet drinks did not cause weight gain.
And in a study published just this month by Blackburn et.al. a group of 163 obese women in a weight loss program were randomly assigned to a group using aspartame or one abstaining from aspartame. Initially, both groups lost about 10% of their body weight. But during follow-up the aspartame group lost significantly more weight overall, and regained less weight. Again, aspartame was not shown to cause weight gain.
There are a number of other studies with similar conclusions. A 2009 study by Brown reviewed 18 studies of weight loss and gain in children with the express purpose of studying weight gain associated with aspartame, and decided that that there was “no strong evidence for causality regarding artificial sweetener use and metabolic health effects.”
A study in the European Journal of Clinical Nutrition compared satiety scores for milk, sugar sweetened beverages and artificially sweetened beverages. They found no evidence that artificially sweetened beverages increased appetite or energy intake. And a paper by Maersk and Belza found that “diet cola had effects similar to water.”
Lest you think these are somehow “cherry-picked” results, all of these papers came up in simple PubMed searches for “aspartame” and “obesity,” and represent just about all the recent papers in the field. There are no papers indicating that aspartame contributes to obesity or to diabetes.
Finally, the Academy of Nutrition and Dietetics has taken the position that consumers can safely enjoy a range of nutritive sweeteners and nonnutritive sweeteners.
In conclusion, the idea that aspartame and other non-nutritive sweeteners actually contribute to obesity is just not borne out by actual research.