I recently met a slender, health-conscious young woman who insisted that the size of sugar-sweetened drinks should not be legislated. "Getting people to drink less of them should be done through education," she said.

It is an opinion shared by many others. Some may be unaware of the role that these beverages are playing in the nation's burgeoning epidemics of obesity and Type 2 diabetes. Few know the disappointing history of efforts to change human behavior solely through education.

The young woman was reacting to a New York City regulation, to take effect on March 12, limiting to 16 ounces the size of sugar-sweetened soft drinks available for purchase at restaurants, street carts, movie theaters and sporting events. The Barclays Center in Brooklyn, the new home of the Nets, has already imposed this limit. Convenience stores, vending machines and some newsstands are exempted from the regulation.

Several new studies underscore the public health potential of the restriction. If it succeeds in curbing the consumption of sweet liquid calories, it is likely to be copied elsewhere, because the nation's love affair with super-size sugary soft drinks is costing cities and states billions of dollars annually in medical care.

Sweet Tooth Run Amok

We are all born with a natural preference for sweetness, which through evolution enabled us to know when fruits and berries were ripe and ready to eat. But as Gary K. Beauchamp, a biopsychologist and director of the Monell Chemical Senses Center in Philadelphia, has put it, "We've separated the good taste from the good food." Our sweet tooth is no longer working to our advantage.

No one is claiming that sugar-sweetened drinks are the only reason Americans have gotten fatter and developed high rates of Type 2 diabetes. But at no time in history have we eaten more caloric sweeteners than we do today, and soft drinks are the main culprit.

Sugar-sweetened drinks, the single largest source of calories in our diet, account for nearly half of the total added sugars we consume and 7 percent of our total calories - nearly 15 percent in some groups, including adolescent boys. University of Wisconsin researchers reported in 2005 that the average student consumes 31 pounds of sugar in sweetened beverages annually.

Coca-Cola once came in eight-ounce bottles with 97 calories. Today people buy 12-ounce cans with 145 calories (the equivalent of 10 teaspoons of table sugar); 20-ounce bottles with 242 calories; 32-ounce Big Gulps with 388 calories; 44-ounce Super Big Gulps with 533 calories; and 64-ounce Double Gulps with 776 calories. There are but small differences in price among these choices.

These calories are nutritionally empty, unlike those from fruits, vegetables, meat, poultry, fish and dairy products, all of which are life-sustaining sources of essential nutrients.

Barbara J. Rolls, professor of nutritional sciences at Penn State, has shown that liquid calories lack a sufficient "satiety factor." When people consume soft drinks, they don't compensate adequately by eating fewer calories from solid foods.

Brian Wansink, director of the Food and Brand Laboratory at Cornell University, explained that beverages aren't as filling as solid food because they lack texture and "mouth feel," and we "tend to consume them so fast they don't register."

Many observational studies have linked consumption of sugar-sweetened beverages to weight gain in children, and to weight gain and Type 2 diabetes in adults. But the new research goes well beyond those findings.

In one study among women followed for four years, consuming one or more of these drinks per day nearly doubled the risk of developing Type 2 diabetes, compared with women who drank fewer than one a month. And the authors concluded that those who increased their consumption of sugary drinks also "increased energy intake" - calories, that is - "from other foods, indicating that these beverages may even induce hunger and food intake."

Two recent studies, published in The New England Journal of Medicine, looked at the effects on weight in children and adolescents when sugar-free beverages were substituted for those with caloric sweeteners. In both cases, limiting sweet liquid calories curtailed weight gain in children, compared with those who continued to consume sugared drinks.

The authors of one of the studies, conducted in the Netherlands, noted, "Children in the United States consume on average almost three times as many calories from sugar-sweetened beverages," compared with Dutch children.

As you might expect, soon after the end of the other study, conducted among adolescents in the Boston area, the youngsters reverted to consuming readily available sugary drinks, which speaks to the importance of both education and regulation. Dr. David S. Ludwig, an expert in childhood obesity and the study's senior author, said the findings emphasized the need for public policy changes.

"It suggests that if we want long-term changes in body weight, we will need to make long-term, permanent changes in the environment for children," he told The New York Times when the report was published.

A third study, published with the first two, found an important link between genetics and the effects of sugary drinks on weight. Men and women with a genetic predisposition to gain weight experienced a more pronounced effect from sugar-sweetened beverages than did people lacking 32 genes associated with greater body mass index.

Improving Health Habits

Education matters. If I didn't believe that, I would have long since abandoned my role as a public health educator. But history has clearly shown that teaching people what is good for them is not enough. It must be accompanied by restrictions that curb unhealthy habits and environmental changes that foster healthier ones.

Cigarette smoking is a classic example. Myriad well-publicized reports documenting its hazards - even warnings on cigarette packs - did relatively little to get people to quit smoking and keep others from taking it up. It was not until smoking was banned in workplaces, restaurants, public buildings and transportation that smokers became social pariahs and millions gave it up. Today only about one American man in five smokes, down from nearly one in two 40 years ago.

Just as the tobacco industry disputed the link between smoking and lung cancer for many years, claiming the evidence was circumstantial and did not prove cause and effect, the American Beverage Association says that there is no proof that sugary beverages are major players in obesity and diabetes.

But why wait decades for conclusive evidence, by which time millions will have been sickened or died from obesity? If there were an environmental threat with even a fraction of the health risk posed by sugary drinks, there would surely be a large public protest.

It is not as if there are no readily available alternatives to sugar-sweetened drinks, including ones with noncaloric sweeteners and waters with and without carbonation, flavored or plain. If such beverages were less expensive and prominently displayed, and more venues limited the size and availability of sugared drinks, we could start on the path so well trod during our antismoking efforts.