Do sugar substitutes really help people lose weight?

Companies advertise their artificially-sweetened foods as being almost magical weight-loss potions. Do they really help? In theory and in some studies, yes. In practice, it depends. Here’s what we know.

As most people find out the hard way, losing weight is difficult and it takes a concerted effort to eat fewer calories and exercise more. Artificial sweeteners and other sugar substitutes can make the struggle a little more pleasant. The challenge is not making up the skipped calories by eating more of other foods.

studying sugary foods vs artificially-sweetened foods

A number of clinical studies have compared the effect on body weight of eating sugary foods and beverages versus the effect of eating comparable artificially-sweetened products. A recent review of the evidence on diet beverages concluded that the risk of obesity may be lower when artificially sweetened beverages replace sugar-sweetened beverages, but that we need addi­tional research to be sure.

Moreover, the federal government’s Dietary Guidelines for Americans, the Ameri­can Heart Association, and the American Diabetes Association say that sugar substitutes may help with weight management, but that the evidence is limited.

but do artificial sweeteners cause weight gain?

Some people claim that artificial sweeteners actually cause people to gain weight. Those claims are sometimes based on studies that found that people drinking diet soda were more likely to be overweight or obese than others who were not drinking diet soda. But that does not prove that diet soda or artificial sweeteners caused their obesity or weight gain. People who are overweight or obese may simply be consuming diet soda in an attempt to lose weight.

A recent well-designed randomized controlled trial—the strongest kind of evidence— found that diet soda doesn’t cause weight gain. Researchers assigned 641 children to drink a cup a day of soda sweetened with either sugar or with non-caloric sweeteners for 18 months. The drinks tasted and looked the same, and the researchers measured sucralose in the urine to make sure the children assigned to the sugar-free beverages actually drank them. Those who got the regular soda gained more weight (and fat).

Also, a recent industry-sponsored meta-analysis (in which the results from numerous small studies are combined into one analysis) of randomized controlled trials—found that substituting low-calorie foods and beverages for their regular-calorie versions results in a modest weight loss and may be a useful dietary tool to improve compliance with weight-loss or weight-maintenance plans.

do artificial sweeteners cause metabolic changes that affect weight?

Another argument that artificial sweeteners hurt more than help dieters is based on the finding that sugar substitutes can interact with sweet-taste receptors not only in the mouth, but also in the gastrointestinal tract and pancreas. Test-tube studies show that when sugar substitutes interact with those receptors, they cause gut hormones to be secreted and other metabolic changes that could affect the regulation of body weight. However, most studies in humans have not detected such effects. Scientists are still working to understand the significance of those curiously situated sweet-taste receptors and their interaction with sugar substitutes.

artificial sweeteners and the bacteria that live inside us

Some researchers say that artificial sweeteners may be derailing weight-loss efforts by changing the ecology of the bacteria and other microbes—roughly 100 trillion!—in our digestive tracts.

Scientists are learning how important the “microbiome” in our bodies is to our health.A widely publicized 2014 study concluded that artificial sweeteners may have contributed to the obesity and diabetes epidemics by altering bacteria in the gut. The results suggested that the artificial sweetener saccharin might trigger metabolic problems in some people by changing their microbiome.

However, the study focused on saccharin and can’t be generalized to all artificial sweeteners. And although the FDA considers the amount of saccharin used in the study to be safe, it is far higher than what most peo­ple actually consume. Furthermore, one part of the study looked at only seven healthy adults consuming saccharin for one week. That’s too small and too short of a study to draw firm conclusions about effects over the long-term.

The results, while provocative, don’t negate well-designed studies that find that people are more likely to gain weight on sugar-sweetened beverages and more likely to lose weight on calorie-free beverages. But they do deserve further study.

Sources: Nutrition Reviews 2013; 71(7): 433-440; Diabetes Care 2012;35:1798-1808; N Engl J Med 2012;367:1397-406; Am J Clin Nutr 2014; 100 (3):765-777; J Clin Endocrinol Metab 2012; 97(8): 2597–2605; ce by altering the gut microbiota. Nature 2014 514:181-6.

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