It's rather obvious that people are not rats, but there must be some confusion as many news outlets are trumpeting the results of a rat feeding study as though they could be applied directly to humans. Major newspapers and TV stations, as well as various Internet outlets have posted headlines stating or suggesting that the non-caloric sweetener saccharin can lead to weight gain. What gives? Are there really data substantiating such a conclusion, or was it just a slow news day?
The research in question, by scientists at Purdue University, examined the effect of sweet tasting foods — both artificially sweetened by saccharin and sweetened by glucose — on the number of calories rats consumed subsequently. The researchers were examining the hypothesis that when a sweet-tasting food didn’t have calories, the animals' energy-control system would be affected, and the rats would eat more calories at subsequent meals. Thus, after consuming saccharin-containing foods, the animals would have a propensity to gain weight and excess body fat.
In this study, the test food was low-fat, plain yogurt. The rats were divided into three groups: one group got yogurt that was sweetened with glucose (caloric sweetener); one group's yogurt was sweetened with saccharin (non-caloric sweetener); the third group's yogurt was unsweetened. The animals were given the yogurts six days per week for five weeks, and at the end of that period their body composition was determined. The researchers found that, indeed, the animals who had eaten the saccharin-sweetened yogurt ended up weighing more and also had more body fat than the other rats. So the results of the study seemed to support their hypothesis. But what does that have to do with people?
There are problems with extrapolating the results of this study to humans. First, the sweet stimulus was glucose, not the sucrose (table sugar) that people typically use — and glucose is much less sweet than table sugar. And perhaps more important, there are good data indicating that people don't regulate their calorie intake — we regulate the volume of food we consume. That is, when we eat enough to feel full, we stop eating. That's why eating foods containing a lot of water and fiber (plant foods) is a good scheme to help people control their weight.
Finally, it's well-known that people's food intake is influenced by a host of social and environmental factors — ones that just wouldn't apply to rats isolated in cages.
So for all these reasons, it's extremely unlikely that the results of this study could realistically be applied to people. What’s hard to understand is why it generated as much media attention as it did.