Weighing in on sugar substitutes
Artificial sweeteners—used in countless “sugar-free” products, from sodas, fruit drinks, and candies to baked goods, yogurt, jams, and ice cream—are often thought of as weight-loss aids since they have few or no calories. And more people than ever, overweight or lean, are consuming them in “diet” foods and beverages—about 40 percent of adults and 25 percent of children in the U.S., which is a large increase from about 20 years ago, according to a study in the Journal of the Academy of Nutrition and Dietetics.
The four most popular artificial non-nutritive sweeteners are aspartame, sucralose, saccharin, and acesulfame K. There are also “natural” non-nutritive sweeteners, including stevia and monk fruit extract—though they are not quite as natural as many people think, since they typically also undergo much processing. For simplicity, we will refer to all of these sweeteners collectively as sugar substitutes.
Can they help you lose weight?
It would seem to make sense that, all things being equal, replacing sugar calories with zero-calorie or very-low-calorie sweeteners would cut your total calories and thus help with weight loss, or at least help keep you from gaining weight. But is there evidence that they actually can help people stay thin?
Numerous studies have sought to answer that question, but have consistently yielded inconsistent results. Some studies have found that consuming foods and beverages that contain sugar substitutes can indeed help with weight loss, but others suggest that they can contribute to weight gain. Still others have found no effect on body weight. The studies have focused on the four most commonly used artificial sweeteners listed above. There’s little research on the effect of the “natural” ones, such as stevia and monk fruit, on weight control.
Why such contradictions?
Some research suggests that, in the absence of sugar, people may compensate by eating more fat and protein. Another idea is that sugar substitutes cause taste distortions that lead to increased appetite for very sweet, high-calorie foods. Or people who consume diet foods may not lose weight because, feeling “virtuous,” they may reward themselves for the “saved” calories by eating more of those or other foods—the so-called health halo effect.
There is also emerging evidence, both in lab studies and in people, that sugar substitutes may cause metabolic dysregulation such that the body increases fat production. This may, at least in part, be due to the sweeteners causing changes in the gut’s bacterial population (the gut microbiota). And they may have different physiological effects in overweight versus normal-weight people and in people with diabetes.
On the other hand, when sugar substitutes are associated with weight loss, it may not necessarily be because of them. People who consume lots of diet foods are often overweight to begin with. And when they lose weight, it could be because they take other weight-control steps as well. That is, the use of sugar substitutes may simply be a marker for their weight-loss efforts.
Most studies on these sweeteners are observational (as opposed to clinical trials) and don’t tease this out. Here are a few examples of the contradictions seen in the research on sugar substitutes.
They can help you lose weight
- A 2014 analysis of 15 randomized, controlled clinical trials—which provide the highest-quality evidence—in the American Journal of Clinical Nutrition concluded that using sugar substitutes in place of sugar results in small weight loss (about 2 pounds, on average), as well as reductions in body fat and waist circumference, “and may be a useful dietary tool to improve compliance with weight-loss or weight-maintenance plans.” The studies lasted from 3 to 78 weeks and included a total of more than 3,000 people.
They make no difference
- A well-designed clinical trial in the International Journal of Obesity in March 2017 found no difference in calorie intake over the course of a day among 30 men, whether they were “preloaded” with drinks sweetened with aspartame, monk fruit, stevia, or sucrose (table sugar). When the participants drank the diet beverages, they tended to compensate for the calorie savings by eating more food at meals.
- A 2012 study in Obesity of close to 700 adolescents found no association over two years between consumption of diet sodas and either body weight or body fat. This was after the researchers adjusted for such variables as total calorie intake, physical activity, puberty, race, and socioeconomic status.
- A review of seven clinical intervention trials, published in the journal CMAJ in July 2017, found that consumption of sugar substitutes—including aspartame and stevia—“was not generally associated with weight loss among participants…except in long-term trials with industry sponsorship.” The trials, which involved more than 1,000 participants who were overweight or obese or had hypertension, lasted from six to 24 months.
They may make you gain weight (or girth)
- Also in the 2017 CMAJ study, the researchers analyzed 30 population studies involving more than 400,000 people followed for about 10 years on average. While the clinical studies discussed above showed no effect of sugar substitutes on body weight overall, these observational studies linked them to modest weight gain over the long term. Most of the studies controlled for variables that can confound results, such as baseline body weight, diet, age, and physical activity, though researchers can never identify all of them. Regular consumption of sugar substitutes was also linked to possible adverse metabolic and cardiovascular events (see Diet Drinks, Dementia, and Strokes box).
- The San Antonio Heart Study, a long-term observational study that tracked the dietary intake of more than 3,600 participants over seven to eight years, found that body mass index (a measure of body weight) was higher among consumers of artificially sweetened beverages than among non-users. Those who drank more than 21 such beverages a week were about twice as likely to become overweight or obese as those who consumed none. The study, published in Obesity in 2008, acknowledged that the association by itself does not establish causality, but it raised a troubling question: Are diet beverages “fueling—rather than fighting—the very epidemic they were designed to block?”
- A 2015 study in the Journal of the American Geriatrics Society followed 750 Texans ages 65 and older from the same San Antonio Heart Study; most were overweight or obese; half were Mexican-American. Over a nine-year period, those who drank diet soda every day gained 2 more inches in waist circumference, on average, than those who drank none, even though they didn’t gain more weight. The researchers controlled for sex, ethnicity, age, activity level, initial weight, and other factors, but complete dietary intake data were not available.
- In utero exposure to artificial sweeteners may predispose infants to obesity, according to a 2016 study in JAMA Pediatrics. Babies born to women who drank artificially sweetened beverages daily during pregnancy were about twice as likely to be overweight at age one as those born to women who didn’t drink them, with no differences seen for sugar-sweetened drinks. This was not explained by the mother’s age or calorie intake during pregnancy, or by other potential confounding factors that the researchers controlled for. And the effects were similar in overweight and normal-weight mothers.
Experts weigh in
Despite the contradictory research findings, a 2012 Scientific Statement from the American Heart Association and the American Diabetes Association concluded that when used judiciously, sugar substitutes may help with weight loss or control. But it also concluded that more research is needed. And here’s how the 2015 Dietary Guidelines for Americans sum it up: Sugar substitutes “can help you cut down on calories. But they may not be a good way to manage your weight in the long run.”
It has been surprisingly hard to prove that sugar substitutes help people control their weight. In fact, as these products have grown in popularity, Americans have only grown fatter. That doesn’t mean that sugar substitutes are the culprit, of course, since so many other factors come into play regarding weight gain and obesity, but it also shows they are not the antidote to obesity. Still, when combined with other small yet sustainable calorie-cutting steps and consumed in the context of a healthy diet and mindful eating, sugar substitutes may help some people stay thin—or at least not gain weight.
Keep in mind also that while the weight-control benefits of sugar substitutes may still be unclear, the many health risks associated with high intakes of added sugar—including obesity, diabetes, and heart disease— are indisputable. On the other hand, sugar substitutes can be a marker for an unhealthy diet. A better alternative all around is to cut down on sweetened foods (however they’re sweetened) and opt for water or seltzer instead of diet or regular sodas.