Susan Swithers, PhD
Susan Swithers, PhD, an associate professor of psychological sciences at Purdue University, West Lafayette, Indiana.
Wouldn’t it be ironic if something that’s supposed to help you lose weight actually causes weight gain? While most people believe that using low- or no-calorie sweeteners is a helpful strategy when trying to shed pounds, some researchers are saying don’t be so sure.
Susan Swithers, PhD, an associate professor of psychological sciences at Purdue University, led a study involving rats fed yogurt sweetened with either glucose, a natural sugar, or saccharin, a non-caloric artificial sweetener derived from — believe it or not — coal tar. The results turned conventional wisdom on its head: Based on a series of experiments, the animals fed the artificially sweetened food consumed more calories and gained more weight and more body fat than the animals in the glucose group. All of these differences were statistically significant.
The researchers believe Pavlovian conditioning, a form of learning that involves associating events with their outcomes, may explain the phenomenon. It seems a sweet taste primes the body for the arrival of calories, leading to physiological changes such as rise in body temperature and release of hormones like insulin. But when the animals who were fed the artificial sweetener didn’t receive as many calories as their bodies expected, they still gained weight. What’s more, their body temperature was low compared with the animals in the natural sugar group, meaning that they tended not to burn calories. Dr. Swithers said that if the same mechanism occurs in humans, then people who use low- or no-calorie sweeteners over time could gain weight.
The findings are important, given that obesity rates have risen to 30% today, compared with 15% in 1987. In 1987, the number of people consuming sugar-free sweetener products rose from less than 70 million to more than 160 million in 2000. Is a link probable? There has been an increase in the use of no- and low-calorie sweetened foods, but critics point out that portion sizes and overall calorie intake have also increased, while physical activity has decreased. Besides, they argue, findings in animal studies may not apply to people.
The Purdue researchers agree that artificial sweeteners (including saccharin and other substitutes) aren’t the sole cause of obesity, but contend they may be a contributing factor, saying that other studies corroborate their findings.
But what about the belief that people who use artificial sweeteners lose weight? “Some people can lose weight by using a conscious process like counting calories. For them, artificial sweeteners used in moderation may be useful,” says Dr. Swithers. “But artificial sweeteners may derail the unconscious process in which sweet taste predicts the delivery of calories, and actually make it physiologically harder to lose weight.”
