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For years, dieters and non-dieters alike have relied on sugar substitutes to flavor food and drinks like coffee, tea and diet soda. Although there was little evidence to show that they really helped with weight control, any thought of life without them seemed unacceptable.

Indeed, in response to public outcry over the loss of what was, at the time, the last remaining sugar substitute, several years ago Congress overrode the ban on saccharin, allowing it to stay on the market even after some data suggested it caused cancer in some laboratory animals. Ordinarily under federal law, any substance discovered to cause cancer in any animal species, regardless of the dose at which it's given, must be banned.About five years ago, however, a team of researchers found that another sugar substitute, aspartame, had a surprising effect. When fed to a group of male and female volunteers, it increased their perceptions of hunger. This finding raised questions about all sugar substitutes. If the results were correct, and if heightened feelings of hunger in turn led to increased food intake, then sugar substitutes may make losing weight more difficult.

In this widely publicized study, subjects were given a drink containing either glucose (a form of sugar), aspartame in water, or plain water. Over the period of an hour they were asked about their desire to eat and to rate how full they felt. While subjects felt less hungry and less motivated to eat when given glucose, the opposite effect was observed when they were given aspartame. In their next report, the same group of researchers recorded that not only aspartame but saccharin and acesulfame-K all raised hunger ratings. Unfortunately, the subjects were not offered food so it was hard to tell whether feeling hungrier would have translated into eating more.

Since that time, numerous studies have explored the more practical question: Do sugar substitutes actually affect food intake and weight? Recently, in the American Journal of Clinical Nutrition, Barbara J. Rolls of Johns Hopkins University School of Medicine's Department of Psychiatry and Behavioral Sciences reviewed the evidence collected to date.

One important issue at stake was whether these sweeteners have an effect inside the body unrelated to their taste. Seeking the answer, researchers gave subjects coated sweeteners masking the taste and examined the impact on hunger ratings, food intake and weight change. In studies using large doses of aspartame, there was no effect on either hunger ratings or food intake.

Other studies focused on food intake alone. Short-term experiments with rats and a single study among humans suggest that saccharin consumption may be followed by increased eating.

The effects of aspartame have been examined in much more depth. Some studies have shown that perceived hunger increased following consumption of aspartame, while other studies have not. More importantly, there is no evidence that aspartame has any impact on food intake. In fact, some research actually found that food intake fell after aspartame-sweetened food was given. Similarly, there's no evidence linking aspartame use to weight gain, even when large doses are given over a prolonged period, as long as 24 weeks.

Most of the research on effects of sugar substitutes however, was conducted over brief periods. They provide no information about the effects of long-term use.

As Dr. Rolls points out in her review, these studies were done mainly in normal weight, non-dieting subjects who were unaware whether they were getting an artificial or a caloric sweetener. In the "real world," the effect of substituting a calorie-free sweetener for a caloric one will depend on the individual's motivation. If you use it as an excuse to eat other high-calorie foods, obviously it will interfere with weight loss, or even promote weight gain. You're in trouble if you adopt the attitude that, as one wag put it, "if you drink a diet soda with a candy bar, the calories in the candy bar are canceled out by the diet soda."

Certainly we need to learn more about the actual effect of artificially sweetened foods and beverages on weight control. At this point, though, we can say that consuming these products doesn't seem to promote food intake and weight gain in dieters. In other words, it won't sabotage your efforts to shed pounds. But by the same token, sugar substitutes definitely are not a cure-all. Used in moderation, however, they do allow the extra flexibility that can make the task of losing weight and keeping it off just a little bit easier.

1991, Washington Post Writers Group