“The data are pretty compelling that we should basically cut out sugar-sweetened beverages,” says Frank Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health.
Sugary drinks—soft drinks, sports drinks, energy drinks, fruit drinks, and sweetened teas—are a double whammy.
First, “there is strong evidence that sugar-sweetened beverages lead to weight gain because people tend to not compensate for liquid calories by reducing calories elsewhere,” says JoAnn Manson, director of preventive medicine at Brigham and Women’s Hospital in Boston.
For example, in the largest study done so far, people who were randomly assigned to drink just one cup of sugar- sweetened soda every day for 1½ years gained more weight (and fat) than those who drank a diet soda.
But sugary drinks aren’t just fattening. When Manson and other researchers tracked roughly 75,000 nurses and 39,000 health professionals for 22 years, those who drank a sugary soft drink at least once a day had about a 30 percent higher risk of diabetes than those who drank one less than once a month. And that was after taking weight into account.
“So increased weight didn’t account for all of the higher risk of diabetes,” says Manson.
Even those who drank fruit juice at least once a day had a 21 percent higher risk than those who drank juice less than once a week. And that also was over and above the impact that juice has on weight.
“It doesn’t matter whether it’s fruit juice or soda, the high consumption of sugar in liquid form may lead to weight gain and may pose a major stress on the pancreas,” says Manson.
Researchers aren’t sure why, but evidence is mounting that fructose—found in sweeteners like table sugar, high fruc¬tose corn syrup, honey, and agave—may make the body resistant to insulin.
“We now have two studies that show that a high level of fructose impairs insulin sensitivity,” says Kimber Stanhope, of the University of California, Davis.
When her research team gave middle- aged overweight or obese people a hefty daily dose (25 percent of their calories, or about 600 calories’ worth) of either fructose or glucose for 10 weeks, insulin sensitivity was worse in those who got fructose. And although both groups gained about the same amount of weight, the fructose group gained more visceral (deep belly) fat, which is linked to diabetes.
And Swiss researchers saw a drop in insulin sensitivity in the liver when they gave lean young men only about 14 percent of their calories from fructose—320 calories’ worth—every day for three weeks. (That’s about twice what the average person consumes.)
“We believe that insulin resistance develops first in the liver and then in the rest of the body,” says Stanhope.
“While it’s not definitive, there is data to suggest that consumption of excess fructose- containing sugars reduces insulin sensitivity. And that’s a risk factor for diabetes.”
Sources: N. Engl. J. Med. 367: 1397, 2012; Am. J. Clin. Nutr. 2014. doi:10.3945/ajcn.113.079533; BMJ 347: 150001, 2013; J. Clin. Invest. 119: 1322, 2009; Diabetes Care 36: 150, 2013.