Are Artificial Sweeteners Fattening?

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By James J. Kenney, ?PhD, FACN

The US Food and Drug Administration (FDA) currently approves six different calorie-free sweeteners: acesulfame, aspartame, neotame, saccharin, Stevia/Truvia, and sucralose. Whether or not these nonnutritive sweeteners (NNS) have an impact on calorie intake and body weight has been debated for many years. Certainly these NNS are hundreds to thousands of times sweeter than sugar and by themselves contain no significant amount of energy. Thus, they cannot directly cause weight gain. However, it is possible that people who routinely use these NNS may wind up desensitized to sweetness. This could result in increased cravings for very sweet foods and possibly promote weight gain. Other researchers have suggested that NNS might impact body weight by altering the gut microbes or by triggering the release of increased insulin.

There is concern that healthier and more satiating foods such as fruits and vegetables may become unappetizing compared to more processed junk foods sweetened with NNS. If so, the overall quality of the diet might decline. This might lead to the return of calories that had gotten displaced from the diet by the sugar for NNS swap. Those calories could end up sneaking back into the diet from more refined carbohydrates and the low-quality fats in processed foods made more palatable as a result of NNS. Dr. Ludwig at Harvard speculated that “sweetness receptors” in fat cells might be stimulated by NNS. He suggested that this “… raises the possibility that artificial sweeteners could cause weight gain by directly stimulating the development of new fat cells.” (Dr. Ludwig is a professor of pediatrics at Harvard-affiliated Children’s Hospital Boston, and was quoted in a Health Letter article). And there certainly is population data showing that people who use more NNS are more likely to gain weight over the next year or so when compared to subjects who mostly avoid NNS. It is clear that, over the past 50 years, Americans are both becoming fatter (on average) and consuming more NNS. But such observational data are confounded by the fact that it is the people who are prone to weight gain who are much more likely to chose to consume more foods and drinks with NNS in place of sugar. So the correlation between using more NNS and weight gain may or may not be causal. Reviews of the subject often leave health professionals with no clear answers (1).

There is growing evidence that the consumption of beverage calories — particularly sugar-rich drinks — promotes excessive calorie intake and weight gain. If this is the case, then replacing sugar-sweetened drinks with those sweetened with NNS may indeed aid weight loss or certainly reduce the risk of gaining more weight. Controlled clinical trials comparing sugar-sweetened to NNS soft drinks generally show that sugar-sweetened drinks promote increased calorie intake and weight gain compared to the NNS-sweetened drinks (2). However, while the US Dietary Guidelines state that NNS drinks are preferable to sugar-sweetened drinks, they maintain that drinking water instead of sugar-sweetened drinks is the “gold standard” for weight loss and weight control (3).

Study Shows NNS Beverages Work Better than Water

Dr. Peters and colleagues conducted a study that compared the efficacy of NNS-beverages to water during a 12-week behavioral weight loss program and a 9-month follow-up period. They randomized 303 overweight subjects (BMI 27-40) into two groups. One was instructed to drink at least 24 ounces (oz) of water, while the other was instructed to drink at least 24 oz of NNS beverages daily during the 12-week weight loss program. The water group had to agree to give up drinking NNS beverages for one year. Both groups were allowed to consume foods with NNS. To enhance compliance, both groups of participants were given free coupons for either bottled water or NNS drinks for one year. Aside from the differences in beverage instructions, both groups received the same dietary and lifestyle instruction during the 12-week weight loss program. The average weight lost during the first 12 weeks was 10.09 pounds (lbs) for the NNS group and 8.67 lbs for the water-only group. This difference was not quite significant, but only 43% of the water-only group lost more than 5% of their initial weight, compared to 63.3% of those in the NNS group. That difference was significant. The data from this clinical trial were similar to those observed in a prior study that also compared the impact of NNS drinks, water, and sugar-sweetened drinks on weight loss. In this study, Dr. Tate and colleagues also observed that NNS drinks not only aided weight loss compared to sugar-sweetened drinks but also compared to plain water (4). Couple these two studies with data from the National Weight Control Registry, which shows that people who lost and successfully kept off 30 or more pounds consumed on average about 3 times more NNS drinks than normal weight subjects who never lost weight (5), and it seems likely that switching to NNS drinks instead of water may well make it a bit easier to lose excess weight and keep it off.

Bottom Line: The use of NNS in solid foods has not been shown to promote weight gain or aid weight loss, but it is now clear that people who switch from sugar-containing beverages to those sweetened with NNS likely do lose more weight and appear more likely to be able to keep that weight off in the long term.


  3. Popkin BM, Armstrong LE, Bray GM, et. al. A new proposed guidance system for beverage consumption in the United States. Am J Clin Nutr 2006;83:529-42.
  4. Tate DF, Turner-Grievy G, Lyons E, et. al. Replacing caloric beverages with water or diet beverages for weight loss in adults. Am J Clin Nutr 2012;95:555-63.
  5. Phelan S, Lang W, Jordan D, Wing RR. Use of artificial sweeteners and fat-modified foods in weight loss maintainers and always-normal weight individuals. Int J Obes 2009;33:11`83-90.
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