A glass of soda sitting on a countertop

Switching to diet soda and other foods sweetened with artificial sweeteners or other sugar substitutes may seem like an easy way to improve your health by helping to reduce the amount of sugar you eat. 

But evidence that nonsugar sweeteners aid weight loss, oral health, blood sugar levels, or other health problems is extremely limited, according to a major new research review published in the medical journal The BMJ.

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According to Joerg Meerpohl, M.D., director of Cochrane Germany and senior author of the review, consuming food and drink sweetened with a nonsugar alternative may have a slight benefit, but “we also cannot definitively exclude any harms” from these products. That’s because previous research has connected sugar substitutes and diet sodas to weight gain, heart problems, and type 2 diabetes.

Of course, getting too much added sugar comes with some of the same health risks. Even so, the results of the new review suggest that more research is needed to determine whether sugar substitutes are a good alternative, according to Vasanti Malik, Sc.D., a research scientist in the department of nutrition at the Harvard T.H. Chan School of Public Health, who wrote an accompanying editorial.

“It’s basically saying we don’t know enough,” she says.

What the Study Found

The researchers examined 56 studies that evaluated the health effects of consuming sugar alternatives, known as nonsugar sweeteners or non-nutritive sweeteners.

Some of the studies provided evidence that consuming these sweeteners might have a small beneficial effect on body mass and blood sugar levels. Yet other research showed that people who frequently consumed sugar substitutes gained more weight than those who consumed less of them. For other conditions the study authors looked at, such as diabetes risk and heart disease, there was no benefit or harm associated with sugar substitute consumption.

Some people might think there’s a clear benefit to switching to diet drinks or low-sugar foods sweetened with alternatives, according to Meerpohl. “As our research shows, the evidence for that is not there,” he says.

The Calorie Control Council, a group representing the low- and reduced-calorie food and beverage industry, disputes this conclusion. Referring to sugar substitutes as low- and no-calorie sweeteners, or LNCS, a statement from the group said:

“[I]n contrast to the conclusions made by the study authors, the highest quality scientific evidence shows that the consumption of LNCS results in reductions in body weight, does not lead to weight gain, and does not cause cravings leading to increased intake. . . . LNCS continue to be a useful tool, along with diet and exercise, in helping to support weight management and weight loss.”

Based on what’s in the review, there’s no clear health-related reason for the average person to switch from products sweetened with sugar to alternatives, according to David Seres, M.D., associate professor of medicine at the Institute of Human Nutrition at Columbia University Medical Center. “Why do it if there’s no benefit, even if there’s not much proof of harm, unless you like the flavor?” he says.

Malik, however, sees a potential use for sugar substitutes. Most Americans consume far too much added sugar, getting more than 300 calories (75 grams) a day. Health authorities recommend much less—a maximum of 25 to 50 grams per day. Sugar substitutes might help people cut back.

“The goal isn’t to get people to switch from sugar to diet [drinks]. It’s to get people to switch from sugar to water, but diet [drinks or foods] might be an intermediate way to help them,” Malik says.

She also notes that it’s possible this review didn’t fully capture potential health benefits. The authors included only studies that could specifically identify the nonsugar sweetener used, which eliminates some research on the topic. And in some cases where consumption of these sweeteners was associated with risk for diabetes or weight gain, it may be that the people consuming these “diet” products did so because they were at risk for health problems, which could be why consumption of these products seems connected to those risks.

Concerns About Nonsugar Sweeteners

Past studies have linked low- or no-calorie sweeteners to heart disease, type 2 diabetes, weight gain, and cancer.

Even if some of these links can be explained away because the subjects involved are already in poor health, some of the links could be real. There also have been concerns that nonsugar sweeteners change the microbiome—the bacteria that live in and on us and have significant effects on health—in ways that could increase disease risk. Other researchers have questioned whether people who consume these sweeteners are more likely to develop a taste for sugary foods and drinks throughout their lives, especially if they consume these sweeteners as children, according to Malik.

Additionally, people may not be aware just how much of these sugar substitutes they consume. “We’re seeing some products you wouldn’t think of as ‘diet’ that contain some type of sugar, and a non-nutritive sweetener, such as sucralose or stevia,” says Amy Keating, R.D., a Consumer Reports dietitian. These include sports drinks, fruit drinks, low-fat ice creams, and even English muffins. “It’s possible that manufacturers are trying to keep their products’ sugars count low but still give them a sweet flavor. Consumers wouldn’t know, though, unless they look at the ingredients list.”

And the many nonsugar sweeteners that could appear on that list may have different effects on health, positive or negative. That applies even to sweeteners sold as “natural,” according to Malik. 

What You Should Do

The current review wasn’t designed to provide a definitive answer on the question of whether you should consume nonsugar sweeteners, according to Meerpohl.

Even so, “I would say that there is a good, and safe, alternative for people,” he says. That alternative is “water and non- [or] less-sweetened foods.”

Consumer Reports' experts advise a cautious approach because the study authors acknowledge more research is needed.

“Our recommendation would be to limit added sugars and nonsugar sweeteners,” Keating says. “It could be better to limit yourself to a small glass of regular soda every once in awhile rather than drinking as much diet soda as you want and assuming it has no impact on your health. Better yet, drink water.”  

Editor's note: An earlier version of this article said non-nutritive sweeteners were being used in lower-calorie ice creams. That has been changed to low-fat ice creams.

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