No-calorie sweeteners may actually make it harder for people to control their food intake and lose weight. At least, that's the finding of a new study conducted on rats.
Psychologists at Purdue University's Ingestive Behavior Research Center found that when rats ate yogurt sweetened with zero-calorie saccharin consumed more calories and didn't make up for it by cutting back later compared to rats that ate yogurt sweetened with glucose, which has the same number of calories as table sugar.
The rats that overate gained more weight and put on more body fat.
The study authors, Susan Swithers and Terry Davidson, PhD, think the problem may be that animals that get used to consuming foods an drinks sweetened with artificial sweeteners lose the ability to regulate intake, because the artificial sweeteners break the connection between a sweet sensation and high-calorie food.
They explain that when animals and humans are about to eat sweet foods, the smell and taste of the food, digestive reflexes gear up for that intake. But when the sweetness isn't followed by lots of calories, as in the case with artificially sweetened foods, the digestive system gets confused. Thus, people may eat more than they otherwise would.
The researchers also measured changes in core body temperature as a reaction to the foods the rats ate. Normally when we prepare to eat, the metabolic engine revs up. However, rats that had been grown accustomed to saccharin showed a smaller rise in core body temperate after eating a new, sweet-tasting, high-calorie meal, compared to rats used to food sweetened with glucose.
The authors think this blunted response both led to overeating and made it harder to burn off sweet-tasting calories.
"The data clearly indicate that consuming a food sweetened with no-calorie saccharin can lead to greater body-weight gain and adiposity than would consuming the same food sweetened with a higher-calorie sugar," the authors wrote.
Other artificial sweeteners such as aspartame, sucralose and acesulfame K would likely produce similar results, the authors note.
The findings appear in the February issue of Behavioral Neuroscience, which is published by the American Psychological Association.
These problems that the rats had with regulating the amount of calories they ate might help to explain why obesity rates have continued to rise even as the use of artificial sweeteners has risen as well.
The study findings are consistent with those found in a similar study published in the journal Obesity last year. That study, from researchers from the University of Alberta found that rats that ate diet or low-calorie food tended to overeat, leading to obesity.
The researchers again speculated that the animals learned to connect the taste of food with the amount of caloric energy it provides. When they ate low-calorie versions of foods that are normally high in calories, they may have developed distorted connections between taste and calorie content. So when they ate the full-calorie versions of those foods, they tended to overeat because of the earlier "taste condition", explained study author and sociologist David Pierce.
The authors of this latest study caution that the experiments were conducted on animals and that studies on humans would be needed to see if the results would be similar.
