McAllister: Drinking diet sodas may sabotage diets

If you drink a diet soda instead of the real thing, you probably think you’re doing yourself a favor. After all, you’re missing out on all the sugar and extra calories in regular soft drinks as well as the associated weight gain, right?

As it turns out, you may be temporarily avoiding some unwanted calories, but not necessarily the weight gain.

Researchers at the University of Texas Health Science Center at San Antonio found that the more diet sodas a person drinks, the greater his or her risk of becoming overweight or obese.

“To our great surprise, we found that normal-weight individuals who drank diet sodas gained significantly more weight over a seven- to eight-year period than normal-weight individuals who were drinking regular sodas,” noted Sharon Fowler, a faculty associate in the division of clinical epidemiology at the Health Science Center’s Department of Medicine.

With hundreds of different soft drink brands on the market, Americans are drinking more soft drinks— diet and regular -- than ever before. Data from the American Beverage Association reveal that Americans consume more than 50 gallons of carbonated soft drinks per person per year.

Along with colleague Ken Williams and principal investigator Michael Stern, M.D., Fowler examined the association between consumption of diet and regular soft drinks and weight gain in 622 non-overweight adults. The researchers measured each participant’s Body Mass Index (BMI) and individual soft drink consumption at the beginning of the study, and the participants returned for follow-up measurements seven or eight years later.

After adjusting for age, gender and ethnicity, the investigators found that regular soft drinks were not significantly associated with the development of obesity, but diet soft drinks were.

“Preliminary analysis of the data showed that for every can or bottle of diet soda that a normal weight person drank per day, there was a 65 percent increase in the risk of becoming overweight and a 41 percent increase in the risk of becoming obese for every can or bottle consumed,” Fowler noted.

Fowler admits that the results of the data analysis are as puzzling as they are intriguing, and offered a few possible explanations. “It may be that the normal-weight study participants whose weight was increasing had switched to diet soft drinks in an attempt to stop their weight gain,” she suggested.

On the other hand, it could be that diet soft drinks tended to displace other health-promoting beverages from the diet. Earlier research suggests that the more soda a person drinks, the less likely he or she is to consume water or more nutritious beverages, including milk and fruit juice.

“Milk is a big source of calcium in the American diet, and calcium has been shown to be protective against weight gain,” Fowler said. “It could be that our study participants were drinking diet sodas to the exclusion of milk, and this contributed to their weight gain.”

The link between diet soft drinks and weight gain may be explained in terms of a psychological effect. “Having nobly given up the 140 calories in a can of regular soda, people may feel that they’ve earned a little leeway in their diets, and they may treat themselves to a candy bar along with the diet soda,” Fowler said. “Or they may order the biggie-sized meal at a fast food restaurant instead of the smaller meal.”

Last but not least, there’s a very real possibility that the artificial sweeteners in diet soft drinks actually stimulate hunger, thereby causing people to eat more, and subsequently gain weight. An appetite-stimulating effect of artificial sweeteners has been previously demonstrated in studies of laboratory animals.

“It could be that the sweet taste of diet soft drinks interferes with the body’s ability to calculate the caloric load it’s receiving,” Fowler explained. “Your brain gets the message that food is coming in, but in the absence of calories, it may end up registering hunger.”

The true relationship between consumption of diet soft drinks and weight gain may not be fully understood for years, but one thing is clear. The sweet-tasting beverages are not a magic bullet for staying slim, as many Americans hoped they would be.

“If the human body came with an owner’s manual, it would not recommend the use of diet soft drinks,” Fowler said. “When it comes to preventing weight gain, drinking diet soft drinks cannot replace regular physical activity and a healthy diet.”

Rallie McAllister is a board-certified family physician, speaker and the author of several books, including “Healthy Lunchbox: The Working Mom’s Guide to Keeping You and Your Kids Trim.” Her Website is www.rallieonhealth.com Copyright 2009 Creators Syndicate Inc.