June 30, 2004 -- Sugar substitutes may offer sweet treats for calorie-conscious dieters, but a new study shows that they may also play tricks on the body and sabotage weight-loss efforts.
Researchers say artificial sweeteners may interfere with the body's natural ability to count calories based on a food's sweetness and make people prone to overindulging in other sweet foods and beverages.
For example, drinking a diet soft drink rather than a sugary one at lunch may reduce the calorie count of the meal, but it may trick the body into thinking that other sweet items don't have as many calories either.
But don't ditch your diet drink yet.
"The message is not to give up your diet soda and go drink a regular soda," says researcher Susan Swithers, PhD, associate professor of psychological sciences at Purdue University. "But when you do drink beverages you probably need to pay a little more attention to whether they have calories or not and what the consequences of that fact will be on the rest of your diet."
Sweetness Provides Calorie-Counting Clues
Swithers says that in the past, a food's sweetness provided valuable clues about its caloric content, and something sweet was usually a good source of energy.
"Before things like artificial sweeteners, these relationships would be very reliable," says Swithers. "Animals needed to find good sources of calories and needed to know whether eating something provided them with lots of calories."
"It's only been relatively recently that foods have been introduced that violate those kind of relationships, such as something very sweet that has no calories," Swithers tells WebMD.
According to researchers, the number of Americans who consume sugar-free, artificially sweetened products has grown from less than 70 million in 1987 to more than 160 million in 2000.
At the same time that more people are drinking and eating foods sweetened with low-calorie sweeteners, such as aspartame and saccharin, they're not getting any thinner. In contrast, more people are becoming overweight or obese.
That prompted researchers to test whether not being able to use sensory clues to predict the calorie content of foods might contribute to overeating and weight gain.
Artificial Sweeteners May Trick the Brain
In the study, published in the July issue of the International Journal of Obesity, two groups of rats were fed either a mix of high-calorie, sugar-sweetened, and low-calorie, artificially sweetened liquids; or sugar-sweetened liquids alone. This was fed to the rats in addition their regular diet. After 10 days, they were offered a high-calorie, chocolate-flavored snack.
The study showed that rats fed the mixed liquids ate more of their regular chow after the sweet snack than those who had been fed sugar-sweetened liquids alone.
Researchers say the results show that the experience of drinking artificially sweetened, low-calorie liquids had damaged the rats' natural ability to compensate for the calories in the snack.
Manipulating Food Can Derail Diets
Health psychologist Daniel C. Stettner, PhD, says damaging the body's natural ability to count calories based on food's sweetness is just one way in which food can be manipulated to change eating habits and contribute to obesity.
"We do more to manipulate food than just add artificial sweeteners. The food industry plays with the sugar, the fat, and the salt," Stettner tells WebMD. "It's like a shell game."
Stettner says that when manufacturers lower the sugar content in foods, they typically increase the fat or the salt content to compensate for any change in how it tastes or feels in the mouth. For example, sugar-free ice creams can be made higher in fat content.
"Sugar-free foods can still be calorie-dense, and that can mess up weight," says Stettner, who specializes in weight issues at Northpointe Health Center in Berkley, Mich.
Stettner says the body's natural calorie counter and sense of balance is also affected by genetics, environment, marketing, and physical activity level, which were not taken into account by this study.
"So many factors contribute to obesity," says Stettner. Although artificial sweeteners may alter the eating behavior of rats, he says the same principle may not necessarily apply to humans.
Swithers says that many types of learning processes translate from rats to humans, but she acknowledges that the loss of the ability to judge the calorie content of sweet foods is probably just one of the contributors to the rise in overweight and obesity.
However, she says humans also have a distinct advantage over rats when it comes to controlling how many calories they put into their body.
"Rats can't read the labels, but we can," says Swithers. "We have to take that extra step of reading the labels or asking how many calories are in there. That may be enough so that we can compensate for those sweet calories."