Artificial sweeteners -- those diet-friendly ways to satisfy the sweet tooth -- recently got some bad press. In a study that has spurred discussion among scientists and on dieting blogs, researchers at Purdue University found that rats consuming saccharin-sweetened yogurt ate more food overall and put on more weight during a two-week period than rats consuming glucose-sweetened yogurt.
The rodent finding has led some to ask: Are artificial sweeteners really good for a diet? Or do they, in fact, undermine weight-loss efforts?
Some researchers, including authors of the rat study, say the answer is the latter. Zero- or very-low-calorie sweeteners such as saccharin and aspartame are charlatans, they say -- signaling sweetness without delivering the goods. As a result, the body's Pavlovian association of "sweet" with "calories" -- is weakened, upsetting the ability to balance how many calories are eaten against how many are used up.
The result? Weight control becomes more difficult.
"There's no reason to believe that humans don't do the same thing" as the rats, says Susan Swithers, lead author of the rat study and an associate professor of psychology at Purdue University.
Other nutrition researchers aren't convinced that the rat study applies to people and point to human studies with different results. They say that even if taste signals are weakened in humans consuming artificial sweeteners, any imbalance is likely to be dwarfed by other influences on eating -- including portion size, mindless munching and eating for self-comfort's sake.
"We don't quite know where this fits," said Barry Popkin, a professor of nutrition and director of the Interdisciplinary Obesity Center at the University of North Carolina. "It's another part of the puzzle, the long- and short-term human effects of all the sweeteners that have been added to our diet -- both the caloric and diet -- over the last 20 to 30 years."
The rodent study, published last month in the journal Behavioral Neuroscience, manipulated the signal that sweet taste sends. Rats ate yogurt (some days it was sweetened and other days it wasn't) in addition to their regular chow. Glucose was the sweetener in one group of rats, and saccharin was used in a second group.
The saccharin-eating rats ingested 5% to 10% more calories overall, gained 20% more weight and increased their percentage of body fat by more than 5%. Swithers and co-author Terry Davidson suggest that, by interfering with what sweet taste means, artificial sweeteners upset an ancient physiological system that evolved to regulate food intake and energy use.
