Good news for fans of diet drinks and sugar-free sweets: You can safely ignore the hype about zero-calorie sweeteners somehow triggering weight gain and metabolic issues, according to a team of U.S. and European scientists.
The potential paradox of diet soda fueling weight gain had a lot of traction in popular health media. But this idea was based on inconsistent rodent research results, plus human studies that found links between artificial-sweetener consumption and ill effects but not a causal relationship .
A new article in the journal Obesity Reviews summarizes last year's "Beyond Calories—Diet and Cardiometabolic Health" conference, sponsored by the CrossFit Foundation. The event convened doctors, obesity researchers, molecular biologists, nutrition scientists, and other academics from the U.S., Denmark, and Germany to consider whether all calories are "equal with regard to effects on cardiometabolic disease and obesity."
"There is no doubt that positive energy balance, due to excessive caloric consumption and/or inadequate physical activity, is the main driver of the obesity and cardiometabolic epidemics," write Janet King and Laura Schmidt in the paper's introduction. But there's also evidence that "certain dietary components increase risk" for heart disease and weight gain in ways that go beyond a simple tradeoff between calories consumed and calories burned.
In the case of diet soda and its ilk, there are all sorts of theories about how these drinks could sneakily imitate the effects of sugary beverages. It was posited that they might trigger our sweet taste receptors to crave more sweet things after consumption, that they might alter our gut bacteria in a negative way, or that they induce a biochemical response as if real sugar had been consumed.
Some speculated that "caloric compensation occurs, negating calories 'saved,'" writes Allison Sylvetsky in a section of the article that deals with non-nutritive sweeteners (NNS). "This compensation could be psychological, whereby one's knowledge of consuming a lower calorie NNS containing alternative may lead to giving oneself permission for greater calorie ingestion at subsequent meals," or it "could be physiological, in which consumption of lower calorie NNS containing alternatives promotes heightened hunger and subsequently higher calorie intake."
But that wasn't much more than speculation. "Two separate meta analyses consisting of 10 and eight [randomized controlled trials] both indicated that substituting [artificial sweeteners] for sugar resulted in a modest weight loss in adults," notes Sylvetsky. "In 62 of 90 animal studies, NNS did not increase body weight, and a more recent meta-analysis of 12 prospective cohort studies did not support an association between NNS consumption and BMI."
The most popular artificial sweetener these days is aspartame, which can be found in most diet soft drinks. Acesulfame Potatassium, Sucralose (sold in the U.S. as Splenda), and substances derived from the stevia plant are also popular. The paper cautions that aspartame has much more safety evidence on its side than the others, as it has been studied much more extensively. (There's no particular reason to think the others will prove any less safe, but they've been studied "for periods no longer than 16 weeks.")
Aspartame has been controversial for decades, but fears over its alleged links to everything from Alzheimer's disease to brain cancer, diabetes, leukemia, and weight gain have proven unfounded. (Such was also the case with saccharine before it.) And there have been ample randomized controlled trials to study its effects.
"It does not appear that any of these [trials] revealed adverse effects of NNS consumption on risk factors for cardiometabolic disease," writes Sylvetsky, summing up the research. In one six-month study, overweight and obese participants were assigned to drink either sucrose-sweetened cola, aspartame-sweetened cola, water, or low-fat milk. Researchers found "no significant differences between the effects of aspartame-sweetened cola and water on body weight, visceral adiposity, liver fat and metabolic risk factors."
In "the longest intervention study conducted to date," 163 obese women were randomly assigned to have or avoid aspartame-sweetened foods and drinks during a several-month weight-loss program, a one-year weight-maintenace program, and a two-year follow-up period. "The aspartame group lost significantly more weight overall," reports Sylvetsky, "and regained significantly less weight during the 1-year maintenance and the 2-year follow-up than the no-aspartame group."
Controlled trials "consistently demonstrate" that consuming aspartame and other artificial sweeteners is associated with decreased calorie consumption, the paper concludes. And "there are no clinical intervention studies involving chronic [sweetener] exposure in which [it] induced a weight increase relative to sugar, water or habitual diet."
The team of researchers suggests that more studies should be done on on the effects of artificially-sweetened beverages on children and on how consumption of these drinks is related to glucose tolerance and inflammation.