Calorie-Counting Conundrum: The Diet Foods, Beverages Paradox

You think you’re being “good” when you reach for a diet Coke or opt for the low-fat version of your favorite snacks—but what you think of as calorie-saving substitutions actually may not be saving you any calories in the long run.

A new study, published in the Obesity journal, has added another twist to the growing body of research that suggests a diet-foods paradox: the more low-calorie (or even zero-calorie) sodas and foods you consume, the more your body demands payback for the calories it was deprived.

Led by David Pierce, researchers at the University of Alberta studied the eating habits of young rats, and found that they tended to overeat when they were fed “diet” foods.

The experiment began under the assumption that animals—particularly young animals—are adapted to crave high-calorie foods that are packed with fat and carbohydrates, the crucial biological fuel that rapidly-growing juveniles need. So Pierce trained his rats to associate low-calorie foods with a “diet” taste and high-calorie foods with a different taste (think Pavlov’s dogs).

Then, when the rats were fed a high-calorie food that had been flavored with the diet taste, their brains assumed that their bodies were running low on calories, and they overate at the next meal in an effort to make up for the lost energy.

“Animals have the ability to sense the caloric value of food they take in,” Pierce says. “We found out that an animal can learn to use flavors to predict calories in an attempt to achieve energy balance.”

He adds that this same phenomenon may explain similar results in recent diet studies, such as a recent University of Texas study on diet soda. Researchers in the 8-year study found that, for every can of diet soda consumed, the risk of being overweight increased by 41 percent. There was only a 30-percent risk increase in drinkers of regular, sugared drinks, however.

Another soda study also found that “diet” did not equate to being healthier in regard to metabolic syndrome (the dangerous constellation of risk factors like obesity, high cholesterol and insulin resistance that increases the likelihood of heart disease). In this report, which was part of the Framingham Heart Study, researchers found that all soda drinkers—diet and regular—had a 48-percent higher risk of metabolic syndrome than non-soda drinkers.

However, the study authors conceded that it was impossible to implicate diet drinks completely due to the possibility that those who drank low-calorie beverages were already overweight or at a higher risk of metabolic syndrome and were using diet soda as a means of being healthier.

But Pierce’s lab rat study hints that a basic, biological mechanism may be at work. The animals were able to predict the amount of calories in a food, based on taste, which demonstrates that the body uses cues like taste and texture to determine that it is consuming sufficient fuel. In humans, this may be reflected in the preprogrammed anticipation of sugary, high-calorie fulfillment after drinking a soda or munching on a sweet snack. So, just as Pierce’s rats were fooled into thinking that they hadn’t absorbed enough calories after eating diet food, people may be similarly unsatisfied after eating diet versions of snacks and beverages and inclined to eat more later to make up the difference.

This association between diet foods/beverages and weight gain has not been proven by the studies, but it certainly merits further research—particularly for those in the food and beverage industry, which has invested billions in diet and low-calorie versions of almost every food imaginable.

"This study simply defies common sense," says Dr. Richard Adamson, scientific consultant to the American Beverage Association, in a prepared statement responding to the study. "To suggest that foods and beverages with zero calories contribute to weight gain contradicts the overwhelming body of scientific evidence that supports that they can help you reduce calories and maintain a healthy weight."

Dr. Ramachandran Vasan, lead author of the Framingham study, however, notes, "A zero-calorie drink could produce a metabolic response if it is sweet. It can condition you to develop a preference for sweet things, which can lead to weight gain or metabolic syndrome. So something that is sweet could produce a metabolic effect even if it doesn't have a whole lot of calories.”