Sodas — even diet ones — may be linked with increased risk factors for heart disease and diabetes, researchers said on Monday.
They found adults who drink one or more sodas a day — diet or regular — had about a 50 percent higher risk of metabolic syndrome — a cluster of risk factors such as excessive fat around the waist, low levels of “good” cholesterol, high blood pressure and other symptoms.
“When you have metabolic syndrome, your risk of developing heart disease or stroke doubles. You also have a risk of developing diabetes,” said Dr. Ramachandran Vasan of Boston University School of Medicine, whose work appears in the journal Circulation.
Prior studies have linked consumption of sugar-laden sodas with multiple risk factors for heart disease, but Vasan and colleagues also found the link extends to diet sodas.
The results surprised the researchers who expected to see a difference between regular and diet soda drinkers. It could be, they suggest, that even no-calorie sweet drinks increase the craving for more sweets, and that people who indulge in sodas probably have less healthy diets overall.
The finding comes from a massive, multi-generational heart study following residents of Framingham, Mass., a town about 25 miles west of Boston. The new study included about 6,000 middle-aged men and women who were observed over four years. They all started out healthy, with no metabolic syndrome.
Mystery weight gain
Those who drank one or more soft drinks a day had a 31 percent greater risk of becoming obese.
They had a 30 percent increased risk of developing increased waist circumference — which has been shown to predict heart disease risk better than weight alone.
They also had a 25 percent increased risk of developing high blood triglycerides as well as high blood sugar, and a 32 percent higher risk of having low high-density lipoprotein or ”good” cholesterol levels.
The researchers then analyzed a smaller sample of participants on whom data on regular and diet soft drink consumption was available. Those who drank one or more diet or regular sodas per day had a 50 to 60 percent increased risk for developing metabolic syndrome.
“The part about diet soda is more intriguing,” Vasan said.
He said people who drink soda, whether diet or sugar-sweetened, tend to have similar dietary patterns.
“On average, soda drinkers tend to eat more calories, consume more saturated fat and trans fat, eat less fiber, exercise less and be more sedentary,” Vasan said.
The researchers adjusted for those factors and still observed a significant link between soft drink consumption and the risk of developing metabolic syndrome.
Vasan said there are several theories about how diet sodas could increase a person’s metabolic risk.
Sweet tooth may be to blame
“One possibility is that diet soda is sweet. Maybe drinking something sweet conditions you in such a way that you develop a preference for sweet things,” he said.
“Also, diet soda is a liquid. When you take liquids at a meal, they don’t satiate you as much (as solids),” he said.
Poor overall health habits among diet soda drinker could be partly to blame. Barry Popkin, of the University of North Carolina in Chapel Hill, who has called for cigarette-style surgeon general warnings about the negative health effects of soda, says that much of the market for diet sodas are people who have unhealthy lifestyles and know they need to lose weight — with the other portion being thin people who want to stay that way. That means many people drinking diet sodas have unhealthy habits that could lead to increased heart disease risks, whether they drink diet soda or not.
Another theory holds that the substance that gives soda its caramel color promotes resistance to insulin, which is needed to process calories. The coloring has also been associated with inflammation in animal experiments.
“These are all theories which we have not studied,” Vasan said. “We’d like to see these data tested and replicated or refuted. We’d also like nutrition scientists to conduct additional research to help us understand why diet soda is associated with metabolic risk.”
Susan Feely, president of the American Beverage Association, said the notion that diet drinks are associated with bulging waistlines defies common sense.
“How can something with zero calories that’s 99 percent water with a little flavoring in it ... cause weight gain?” she said.
Without a more definitive explanation, Vasan offers only this advice to diet soda drinkers: “consume in moderation and stayed tuned for more research.”