Posted on Mon, Jul. 26, 2004

Diet of low-fat, low-sugar foods might confuse body

"Use of artificial sweeteners may trick the body into eating more real-sugar foods if the opportunity arises."

By Tara Parker-Pope

The Wall Street Journal

Supermarket aisles are filled with foods that have been stripped of calories, sugar, fat and carbs. But new research suggests that altering foods may actually interfere with the body's instincts and trick people into eating too much.

It has long been known that consumers consciously overeat many diet foods. But what's unusual about the latest research is that it looks at the impact that regular eating of certain foods may be having on the body's unconscious biological mechanisms for regulating food intake.

The question is whether by consistently eating sweet foods with no calories, a person can eventually lose an instinctive ability to distinguish between high- and low-calorie sweet foods. Early studies have shown that babies and young children have an innate ability to judge the caloric content of foods. And though adults can obviously read labels to figure out the calories they're eating, the issue is whether sugar-free or fat-reduced foods also throw off the body's subtle, internal signals about food intake -- causing us to overeat.

In the latest study, researchers from Purdue University looked at whether artificial sweeteners disrupt the body's ability to "predict" the caloric consequences of a food. The study, published in the July issue of the International Journal of Obesity, involved young rats that were fed a steady diet of sweetened drinks for 10 days. One group of rats consumed only sugar-sweetened beverages. A second group received an inconsistent diet -- sometimes real-sugar drinks and sometimes drinks with no-calorie saccharin.

After 10 days, all the rats were given a real-sugar chocolate drink and rat chow. The rats with a history of eating both real sugar and artificial sweeteners ate three times the calories as the rats that always drank the real-sugar drink.

What does it mean? The researchers speculate that the overeating rats had received inconsistent signals about the meaning of sweet. For them, sweet sometimes had calories and other times it didn't, possibly confusing the rats' natural food-intake instincts. But the rats that always associated sweet with calories were able to compensate for sweet calories by eating less.

Although rat studies can't explain the human obesity epidemic, animal studies have long given us insight into certain basic behaviors. Just as Pavlov's dogs drooled at the sound of a ringing bell, even when food wasn't present, so the Purdue researchers suggest we should consider a Pavlovian approach to the obesity problem, looking at how sensory properties of foods can condition our biological instincts about eating.

The study doesn't necessarily implicate diet soft drinks; studies have clearly shown that people lose weight when they switch from sugared soft drinks to diet soft drinks. But the research does fuel a growing concern that processed foods may interfere with our ability to regulate how much we eat. For instance, if one day you eat a regular potato chip and another time you eat a reduced-fat version, the question is whether your body may eventually stop making a distinction between the two, causing you to slightly overeat the next time you encounter a regular chip or any full-fat food.

And at a time when bread is now low-carb, cookies and candy bars are being fused into decadent combinations and ice cream can be fat-free, it's no wonder people are getting mixed signals about foods. "As foods get more and more dissociated from our traditional history with foods, it's going to be harder and harder for us to regulate how much to eat," says Barbara Rolls, a longtime food and behavior researcher at Pennsylvania State University.

But the notion that we are being duped -- either consciously or subconsciously -- into eating more is controversial.

Human studies haven't consistently shown that artificial sweeteners affect eating behavior. One French study, for instance, showed that eating patterns didn't vary among adults who ate a yogurtlike food, whether it was sweetened with sugar or aspartame, says Adam Drewnowski, director of nutritional sciences at the University of Washington.

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