A Challenge: Soda and Obesity

One of every five calories in the American diet is liquid. The nation's single biggest "food" is soda.

In reports to be published in science journals this week, two groups of researchers hope to add evidence to the theory that soda and other sugar-sweetened drinks don't just go hand-in-hand with obesity, but actually cause it.

Not that these drinks are the only cause — genetics, exercise and other factors are involved — but that they are one cause, perhaps the leading cause. Lack of exercise and poor eating habits are far bigger contributors to America's weight woes.

Soft drink consumption rose more than 60 percent among adults and more than doubled in kids from 1977-97. The prevalence of obesity roughly doubled in that time. Scientists say these parallel trends are one criterion for proving cause-and-effect.

Numerous studies link sugary drink consumption with weight gain or obesity. One by Ludwig of 548 Massachusetts schoolchildren found that for each additional sweet drink consumed per day, the odds of obesity increased 60 percent.

Another at Harvard of 51,603 nurses compared two periods, 1991-95 and 1995-99, and found that women whose soda drinking increased had bigger rises in body-mass index than those who drank less or the same.

Biologically, the calories from sugar-sweetened beverages are fundamentally different in the body than those from food. The main sweetener in soda — high-fructose corn syrup — can increase fats in the blood called triglycerides, which raises the risk of heart problems, diabetes and other health woes.

Two studies by Penn State nutritionist Barbara Rolls illustrate this. One gave 14 men lemonade, diet lemonade, water or no drink and then allowed them to eat as much as they wanted at lunch. Food intake didn't vary, no matter what they drank.

The second study gave 44 women water, diet soda, regular soda, orange juice, milk or no drink before lunch. Total intake was 104 calories greater for those given caloric beverages than those given diet soda, water or no beverage. Caloric drinks didn't help women feel any fuller either.

Then there is the "jelly bean study." Purdue University researchers gave 15 men and women 450 calories a day of either soda or jelly beans for a month, then switched them for the next month and kept track of total consumption. Candy eaters ate less food to compensate for the extra calories. Soda drinkers did not.

In rebuttal, Adamson, the beverage industry spokesman, sees no such consistency. He cites a 2004 Harvard study of more than 10,000 children and teens. Consumption of sugar-added beverages was tied to body-mass index gain in boys but not girls, a gender difference that warrants a "jaundiced eye" to claims that soda is at fault, he said.

He also points to a Harvard study finding no link between weight changes and soda consumption among 1,345 North Dakota children ages 2 to 5 — a group that arguably drinks far less soda than teens and adults.