Wired Science Blog:
In a study recently published by Purdue University psychologists in Behavioral Neuroscience, rats given saccharin-sweetened yogurt actually ate more and gained more weight than rats given regularly-sugared yogurt....In the last few years this was becoming suspected. The sweet sensation in your mouth primes your body and so starts a series of metabolic changes. This is another refutation that all calories are the same. This same month another study came out that showed that people who drank diet sodas had a higher incidence of the cluster of symptoms linked to heart disease and diabetes. That showed only a correlation and is not real evidence of diet sodas as the cause but combined with the other studies may indicate that water and unsweetened tea or herbal teas or black coffee may be better for you.
The problem appears to be one of metabolic regulation: when rats ate sugary yogurt, their core body temperature rose, ostensibly to take advantage of a calorie-rich nutrient source. But when rats ate the saccharin-sweetened yogurt, their body temperatures rose only slightly, and they ate more and gained more weight than their counterparts.
How could this be? The mechanisms aren't entirely clear: perhaps the rats, confused by false sweetness, became artificially sluggish, and thus less able to burn calories. Perhaps they were primed by the sweetness to expect a burst of calories, and when that didn't follow, they kept eating and eating. Perhaps both.
It is not clear if all artificial sweeteners are the same but years ago the diet I lost fifty pounds on - The Carbohydrates Addict's Healthy Heart Program - recommended avoidance of artificial sweeteners because of the rise in blood sugar it could cause. I have a friend who only uses Splenda because it is another form of sugar and hasn't been linked to health problems or cancer like some studies show saccharin and aspartame have. Here is a link to the new paperback edition at Amazon.