Q. Can diet soda cause diabetes?

A. A recent study published in Diabetes Care suggests that middle-aged and older adults who drink diet soda daily may be at increased risk of developing diabetes. These results are surprising when you consider that diet soda has no calories or carbohydrates.

Some previous studies have suggested a link between diet soda and a condition called metabolic syndrome. Metabolic syndrome is characterized by high blood sugar, excess belly fat, high blood pressure and unhealthy levels of blood fats. Metabolic syndrome increases a person's risk for heart disease and diabetes.

In the recent study, participants were asked how often they consume certain foods and beverages. Participants who drank one or more diet sodas daily were found to be 67 percent more likely to develop diabetes over time than those who drank none.

Before throwing away all your diet soda, keep in mind that this study does not prove that diet soda is to blame. This and the previously mentioned studies were not randomized control studies, only observational studies. Observational studies can indicate associations, but can't prove that diet soda causes disease.

This is because observational studies cannot control for other factors that may have come into play. Metabolic syndrome or diabetes is rarely caused by a single food or beverage item. It's possible that diet soda drinkers may engage in other behaviors that increase diabetes risk, such as lack of exercise or eating too many calories.

Heredity and age also play a role. Diabetes risk increases with age. It's also possible that people who are drinking diet sodas are giving up healthier beverages.

Experts are unsure why diet soda itself might increase risk, but it might have something to do with the artificial sweeteners in the drinks. It's possible that these drinks could increase a person's cravings for sweets, or for more calories from other foods. More research needs to be done in this area.

This does not mean you should switch to regular soda, which is high in sugar and calories. Neither diet soda nor regular soda has any nutritional value. Regular soda has also been linked to metabolic syndrome in several studies. These study results do suggest that if you drink large amounts of diet soda, and are over the age of 45, you may want to cut down and drink more water, tea or nonfat milk instead.

Amy Tousman is a registered dietitian and certified diabetes educator with Nutrition Unlimited in Kailua. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.