Consumption – many would say overconsumption – of full-calorie soda and other sugar-sweetened beverages has undoubtedly fueled the rise of obesity in the U.S. The number of colas, sports drinks and fruit punches guzzled by the average American doubled between 1977 and 2002. Study after study has demonstrated a link between the amount of liquid calories consumed and the number of pounds gained.
If only the reverse were true as well.
It certainly stands to reason that switching from Coke to Diet Coke – or better yet, to water – would cause people to lose weight. Surprisingly, this connection is difficult for researchers to make. In some studies, people who knew they were saving calories on soda wiped out that advantage by taking extra helpings of food. Perhaps others saw less need to exercise. For whatever reason, cutting back on sugar-sweetened beverages is just not as good for the waistline as you’d expect.
And yet, advocates of a soda tax keep pressing their case – most recently in a Health Policy Report to be published in Thursday’s edition of the New England Journal of Medicine. They insist that raising the price of sugary drinks by means of a tariff will prompt people to buy less, consume less and consequently gain less.
Many researchers have made the case that a soda tax would indeed eat into soda purchases. In multiple studies, they have found that a 10% tax on sugar-sweetened beverages would reduce consumption by 8% to 11%. But, as reported recently in The Times, researchers have almost universally failed to close the loop by showing that reduced consumption leads to lower body mass index.
In their policy report, the soda tax advocates cite four long-term, randomized, case-control trials – the kinds of studies considered the gold standard in medical research. But these trials pretty much fail to show that drinking fewer sugary drinks leads to widespread weight loss. Consider:
- A British study of 644 kids between the ages of 7 and 11 found that the ones who drank fewer carbonated beverages had lower BMIs after one year compared with kids who didn’t. But the difference in BMI wasn’t statistically significant. That means the difference could easily be explained by random chance. This study did find that kids who drank fewer sodas were slightly less likely to become obese.
- A Brazilian study of 1,140 9- to 12-year-olds found that a program to discourage kids from drinking sugary drinks had no effect on overall BMIs. The only group with a statistically significant benefit was overweight girls.
- A Boston study of 103 high schoolers found that those who consumed diet drinks for 25 weeks didn’t lose weight compared with kids who drank regular soda, though there was a statistically significant difference for the one-third of kids with the highest BMIs.
- A Chilean study of 98 overweight children found that those who drank milk instead of sugary beverages didn’t have a statistically significant reduction in body fat, though there was a bona fide increase in lean mass.
None of these shortcomings should be interpreted to mean that soda is some kind of health food. But perhaps it would be useful to explore other public health interventions that are proven to reduce BMI broadly among the two-thirds of Americans who are overweight or obese.
Even if soda taxes don’t cause anyone to slim down, some people say they’re a good idea anyway because the money they raise could be spent on measures aimed at reducing childhood obesity, overhauling the healthcare system, or other worthy objectives that would counteract their regressive impact. President Obama recently told Men's Health magazine that a soda tax could be useful in the fight against obesity.
The authors of the policy report suggest a tax of 1 penny per ounce of sugar-sweetened beverage. For a 20-ounce drink, that works out to a price increase of 15% to 20%. If implemented on a nationwide basis, such a tax would raise $14.9 billion in one year. In California alone, it would generate $1.8 billion, including $188 million in Los Angeles.
Want to dream on? Check out this online calculator to see how much money could be raised by imposing taxes of up to $2 per ounce on a variety of drink categories in each of the states as well as in 25 major cities.
-- Karen Kaplan
Photo: Full-calorie soft drinks and other sugar-sweetened beverages are a persistent target for fat-tax advocates.
Credit: Justin Sullivan/Getty Images