Don't kill yourself. You may have heard of a recent study indicating that rats gained weight when they ate yogurt sweetened with saccharine but not when it was sweetened with glucose. The result sort of flies in the face of why you were eating sugar substitutes in the first place — to help you lose weight.
Relax. There may be less to this story than meets the eye, indicating exactly why you don't make changes based on a single study.
This study has its share of weaknesses, such as studying a very small number of rats — as few as eight in some of the groups. It also uses saccharine, instead of a sugar substitute with a taste closer to that of sugar. There are a number of other flaws as well — enough to prevent drawing real conclusions from the results.
What's more, these results contrast with other studies showing that rats do compensate for calories pretty well when there is no perceptible taste difference.
I actually did one such study years ago as a lowly graduate student. I was all excited about being able to use aspartame (Nutrasweet) before it was released to consumers. We used normal-weight rats and rats that were fattened up with high-calorie, fatty, sugary food, to mimic how many people become overweight. Then we placed them on liquid diets — sweetened with sugar and sweetened with aspartame. The aspartame liquids contained either 20 percent or 40 percent fewer calories.
When the rats got the liquid with 20 percent fewer calories, they just drank more of it and maintained their weight — whether they were overweight rats or normal weight rats. When they got the liquid with 40 percent fewer calories, they couldn't eat enough to maintain their weight and they all lost weight.
Weight Loss 101
Before we go on, remember that there are two things almost no one disputes:
Eat more calories than you need, and you'll gain weight.
Eat fewer calories than you need, and you'll lose weight.
Now let's get to the bigger issue for consumers. This study and any similar study, including mine, only explains obesity from a physiological and metabolic standpoint. That might be okay if we only ate because of internal factors. That is, if we "listened to our body instead of our heads," and all that common-sense stuff. Of course, if we did that, we would have no obesity problem.
Unfortunately, we're not rats. We're humans, and factors such as emotions, the environment, stress, advertising, group pressure, you name it, often affect what, why, and how much we eat, and these factors can't be measured very well in rats.
Any sugar substitute in your diet should be seen only as a tool. Like any tool, you can use it wisely, or not.
Unfortunately, sugar substitutes are increasingly being asked to do a job for which they were never intended. They will not "make" you lose weight. They will only help you to stick to a low-calorie or maintenance diet a little more comfortably.
If you use them to cut calories in a drink, only to overeat somewhere else in your diet, you're going to gain weight, but not because you used a sugar substitute, but because you overate. If you had eaten more wisely elsewhere, and used the diet drink to allow you have a sweeter liquid than plain water, you'd have been ahead of the game by 150 calories or so.