Can soda make you fat?
In what may turn out to be fortunate timing for Mayor Nutter's proposed two-cents-per-ounce tax on sugary drinks, the most comprehensive study yet on the issue was published yesterday.
Researchers followed more than 5,000 young adults for 20 years as they moved around the country and faced changing prices of soft drinks, which were then matched to the participants' dietary choices and health.
Among the findings, published in the Archives of Internal Medicine: A $1 increase in the cost of a two-liter bottle of soda - about 1.5 cents per ounce - translated to 124 fewer calories per day from all sources, 2.34 pounds lower body weight per year, and significant improvement in a measure of heart-disease risk.
The impact of a tax on beverages with added sugar in Philadelphia would likely be greater, said study coauthor Barry Popkin, a professor of nutrition at the University of North Carolina at Chapel Hill, because inner-city children, blacks, and Hispanics all drink more soda than the typical American and also have higher rates of obesity.
Why should beverages have any greater effect on health than other sugar-laden snacks?
Researchers point to two main reasons. One is simply volume: Among adults, consumption of sugar-sweetened beverages has more than doubled in the last half-century. Children now drink more soda than milk.
Second, "from the standpoint of hunger and our metabolism, all calories are not created alike," said David S. Ludwig, a pediatric endocrinologist at Children's Hospital Boston.
When a child drinks a sugary beverage, particularly without food, blood sugar rapidly rises and then crashes, he said, apparently triggering hunger that can lead to overeating. And liquids, unlike solids - even solid sugar - don't lead to satiety.
"The same calories, when they are in jelly beans, seem to be more filling than a sugary beverage," said Ludwig. Eating dessert before dinner will dull your appetite, but drinking soda will not.
Ludwig led a study that tracked drink consumption by 548 children in Massachusetts public schools for 19 months. Its key finding, published in the Lancet in 2001, was that each additional can of sugar-sweetened drink a day increased the odds of becoming obese by 60 percent.
He coauthored another study that followed more than 50,000 nurses - young and middle-aged women - for eight years. That research, published in the Journal of the American Medical Association in 2004, concluded that increased consumption of regular soda was linked to greater weight gain and increased risk of Type II diabetes.
Both studies were included in a 2006 review of 30 research papers that varied by type, population, outcome measures, and other factors. Some found clear links between soda and obesity. Some concluded there was no such association. Some determined a connection only in people who were already obese. At least one linked diet soda to higher body fat along with regular soda.
The wide range of these and other findings led some scientists - and the beverage industry - to question whether there really is a link.
"I would say that there is no one food or beverage that is responsible for the obesity problem in this country. It is a balance of energy. Energy in and energy out," said Maureen Storey, senior vice president for science policy at the American Beverage Association.
But Frank Hu, senior author of the 2006 review published in the American Journal of Clinical Nutrition, said his team found a pattern among the research.
"You really have to look at the overall picture," said Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health. The connection was clearer in some of the larger, better-quality studies, he said, and unclear in some studies that were funded by the industry - a suggestion of bias to which Storey took strong exception.
"I think the evidence is very compelling," said Hu, that consumption of sugar-sweetened beverages leads to an increased risk of obesity in both children and adults. It is even stronger, he said, for diabetes, hypertension, and other metabolic diseases.
The research published yesterday in the Archives of Internal Medicine goes another step, independently linking soda prices, consumption, and health by tracking behavior and risk factors over two decades.
It tracked 5,115 people who were 18 to 30 in 1985-86, as part of a larger study set up to investigate various factors that might influence the risk of heart disease. In addition to the participants' periodic medical exams and reported diets, the Archives researchers added economic information - prices for soda and other foods - for the counties they lived in at various times.
Between 1985 and 2006, soda prices on average declined 48 percent when adjusted for inflation. But individual relocations resulted in price increases about 30 percent of the time. "Let's say you moved from Ouagadougou to New York City. The prices went up for you," said Popkin, the nutrition professor and coauthor who is also an economist.
Using thousands of those price changes, the researchers constructed models for how consumption and health would be affected by various taxes. A tax that is slightly lower than the two-cents-per-ounce proposal in Philadelphia was associated with 124 fewer calories less per day overall.
Popkin, who lived in Philadelphia for two years as a graduate student at the Wharton School, predicted that the Nutter proposal, if it passed, would have a greater impact here because black and Hispanic children drink 30 to 50 percent more sugar-sweetened beverages than white children.
He dismissed concerns that a tax would cost jobs. Diet soda and bottled water, the most likely alternatives, are made by the same companies and sold by the same stores that dispense regular soda, he said, and the added costs overall would not be enough for most people to leave the city to buy groceries.
Although the latest study goes farther than its predecessors, "correlation does not equal causation," cautioned David B. Allison, a nutrition researcher and professor of biostatistics at the University of Alabama at Birmingham.
Philadelphia Health Commissioner Donald F. Schwarz agreed that there was no proof. "From a theoretical point of view, have sugar-sweetened beverages caused the obesity epidemic? I don't know," he said.
"No one action is going to stop obesity." It is a series of actions, policy changes and pilot programs that are likely to make a difference, he said.
He said a soda tax, besides hypothetically reducing consumption, would also provide revenue to subsidize healthy foods, fund nutrition education campaigns, and expand pedestrian and bike networks.
The tax, if fully implemented, would raise $77 million a year - $20 million of which would go toward obesity prevention.
The beverage industry has largely stopped delivering sugary drinks to schools nationwide and has replaced them with lower-calorie options, the industry's trade association said yesterday.
"It's a brand-new day in America's schools when it comes to beverages," said Susan Neely, president and CEO of the American Beverage Association, which represents Coca-Cola Co., PepsiCo Inc., and other major soft drink companies.
The association released a report showing a 95 percent decline in sales of full-calorie soft drinks to schools between fall 2004 and fall 2009.
She attributed the decline to voluntary guidelines adopted by the industry in 2006 under an agreement with the Alliance for a Healthier Generation, a joint initiative of former President Bill Clinton's foundation and the American Heart Association.
The guidelines permit the sale of water, unsweetened juice, and low-fat and nonfat milk, flavored and unflavored, in elementary and middle schools. Diet sodas and sports drinks can be sold in high schools.
Sales to schools make up less than 1 percent of the industry's total sales. Neely said.
- Associated Press