Soft Drinks and Metabolic Syndrome: Is It a Lifestyle Thing?

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DO RECENT FINDINGS linking even diet soft-drink consumption to metabolic syndrome mean, what the heck, you might as well have that sugary cola? Not so fast. It's true that researchers found that people who consumed one or more soft drink daily were 48% more likely to develop metabolic syndrome — a precursor to heart disease and type-2 diabetes — than those averaging less than one soda daily. Soda drinkers were also at greater risk for components of the syndrome, such as obesity, hypertension and unhealthy cholesterol levels.

"We were struck by the fact that it didn't matter whether it was a diet or regular soda that participants consumed, the association with increased risk was present," said senior author Ramachandran S. Vasan, MD, of Boston University School of Medicine. Dr. Vasan and colleagues, including Tufts scientist Paul F. Jacques, PhD, published their results in Circulation.

But the researchers cautioned that being observational, the study did not prove a causal relationship between soft drinks and metabolic syndrome. Indeed, it's possible that soft-drink consumption may be only an indicator of a couch-potato lifestyle. Diet sodas may have been implicated because their consumers are trying to compensate for unhealthy lifestyle choices. Think of it as, "I'll have a Big Mac, large fries — and a Diet Coke."

"It may be that soft drinks condition a person's palate, making them more likely to eat sweet, calorie-rich foods," added lead author Ravi Dhingra, MD, of Harvard Medical School. "These are all theories. We have not proven causality."

The researchers used data from a long-running heart study of residents in Framingham, Mass. They looked at a subgroup of 6,039 women and men, average age 52.9, initially free of metabolic syndrome. Participants reported their dietary habits and were given physicals, including testing for fasting plasma lipid, glucose and triglyceride measurements, all markers for metabolic syndrome.

Metabolic syndrome is a cluster of risk factors that doubles the risk of heart disease and stroke and increases the risk of diabetes. It is defined as having at least three of these risk factors: a waist at least 35 inches for women or 40 for men; fasting blood glucose of 100 mg/dL or more; serum triglycerides of at least 150 mg/dL; blood pressure of 135/85 or more; HDL cholesterol higher than 40 mg/dL for men or 50 mg/dL for women.

Beverage experts commenting on the study were not convinced that diet soft drinks are causing metabolic syndrome. "You've got to realize that in this study the diet soda drinkers were not your normal Framingham person," said Barry Popkin, PhD, of the University of North Carolina, who led the development of the Healthy Beverage Guidelines (see the June 2006 Healthletter). Popkin explains that many of the diet-soda drinkers already had health or weight problems and were drinking diet soda because their doctors told them to — not by choice. When diabetics at baseline were removed from the sample, he points out, the impact was reduced.

Popkin warns against interpreting the study as meaning there's no real difference between diet and regular sodas. "For the consumer, it'd be a very bad message," he says. "It would say, 'Might as well drink regular Coke, if it has the same effect as Diet Coke.' Well, that's not true."

TO LEARN MORE: Circulation, July 31, 2007; abstract at . Healthy Beverage Guidelines .

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