By Tom Farley
People who work in public health have been stirring up a lot of fuss lately about sugary drinks. Besides education and school vending bans, they’ve fought for taxes, warning labels, and - ahem - even a proposal to limit portion sizes. The soda companies feel unfairly singled out, and they correctly point out that sugary drinks make up only 6% of the calories in the American diet. Why are health people so obsessed?
First, it doesn’t take a big imbalance in calories, if it is steady, to cause plenty of weight gain over time. As little as about 200 excess calories per day – or the amount in 16 ounces of soda – across the entire population is enough to explain our entire obesity epidemic. Americans now consume an average of about 150 calories a day from sugary drinks.
For a long time, nutritionists have warned about sugary drinks as “empty” calories. Everyone must take in hundreds of calories a day just to get enough protein and essential nutrients, but sugary drinks don’t offer those. But now it’s clear that those calories aren’t so empty. They’re in the form of sugar, and sugar causes weight gain disproportionately.
If you give lab rats or mice sugar water, they gain weight – more weight, even, than when you give them food that is full of fat. Humans react the same way. Across dozens of carefully-done studies (including the “gold standard” randomized-controlled trials), when people consume more sugar, they gain weight, and when they consume less, they lose weight.
Why might sugar cause weight gain more than any other food packing the same amount of calories? Maybe because sugar, especially when it floods into the bloodstream after someone drinks a soda, triggers an outpouring of the hormone insulin, which causes the body to store fat. That may cause people to be hungry and eat more. In effect, sugary drinks drag other calories along with them. The reverse is true, too: when people cut out sugary drinks, they eat less. For example, in one randomized controlled trial, adolescents assigned to give up sugary drinks (but not given any other instructions on diet) took in 213 fewer calories from the sugary drinks, but 454 fewer calories overall.
Then there’s guilt by association. The steepest run-up of the obesity epidemic was between the late 1970s and about 2000, which was during more-than-doubling of sugary drink consumption. Since the early 2000s, as soda sales and self-reported consumption have been falling, obesity rates are leveling off in adults and falling in young children.
Sugary drinks aren’t our only source of sugar and aren’t the only culprit for the obesity epidemic. But the signs point to their playing a major role causing obesity and diabetes in America. Given the enormity of that crisis – two-thirds of Americans overweight, one in nine with diabetes - that’s a good reason to obsess about them.