News Review From Harvard Medical School -- Studies Link Sugary Drinks, Weight Gain
Three new studies strengthen links between sugar-sweetened drinks and excess weight. The New England Journal of Medicine published them online September 21. Two studies involved children. One included 224 overweight and obese teenagers. They were randomly divided into 2 groups. One group received water and diet drinks delivered to their homes for a year. They were urged to avoid sugar-sweetened drinks and got regular pep talks. The other group got no drinks or advice. After a year, teens who got the free drinks had gained less weight than those in the other group. But a year after the program ended the difference had disappeared. A second study involved younger children who drank sugar-sweetened beverages regularly. Researchers gave each child a canned drink daily. One group got sugar-sweetened drinks. For the other group, the drinks were calorie-free and artificially sweetened. After 18 months, the diet-drink group had gained less weight than the other group. The third study looked at data from three large health studies of adults. Those who had genes that increase obesity risk were twice as likely to become obese if they also consumed a lot of sugary drinks. USA Today wrote about the first and third studies.
By Claire McCarthy, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Sugar-sweetened beverages can make you fat.
That is essentially the message of three studies released today in the New England Journal of Medicine:
- Researchers at Boston Children's Hospital did the first study. They randomly divided 224 overweight and obese teens into 2 groups. Teens in 1 group were encouraged to drink fewer sugar-sweetened beverages. They received bottled water and diet drinks shipped to their homes. Researchers also checked in with them and their parents by phone and in person. Teens in the other group were given no drinks or advice. After a year, teens in the program had gained less weight than those in the other group.
- Researchers in the Netherlands gave a whole bunch of children a canned drink every day for 18 months. Half of the children got a sugar-sweetened drink. The other half got drinks with no-calorie sweeteners. At the end of the 18 months, the children who got the sweetened drinks had gained more weight.
- Researchers looked at data about genes and soda drinking from three large health studies. Among women who had one of the genes that are known to increase risk of obesity, those who drank sugar-sweetened beverages gained more weight. The two factors seemed to work together.
Despite these study results, it's also very clear that sugar-sweetened drinks aren't the whole story when it comes to obesity. So getting rid of them would not be a quick fix for anything.
The studies also looked at people's body mass index (BMI). This is a number based on a calculation involving height and weight. BMI is commonly used to determine who is overweight.
- In all of the studies, BMI increased in both the experimental and control groups. Everybody gained weight, no matter what they were drinking.
- The differences in BMI between those who had the sugar-sweetened drinks and those who didn't were actually pretty small.
- Habits are hard to break. In the Boston Children's study, a year after the program ended there was no difference in BMI between the two groups. Without the intensive program, diets went back to being not so great.
What Changes Can I Make Now?
Whether you are overweight or not, it's best to give up sugar-sweetened drinks. And don't buy them for your children. They have no nutrition, and they add calories that nobody needs. It's very clear that sugar-sweetened drinks are fueling the obesity epidemic in a big way.
Our bodies were designed to eat our calories, not drink them. We can take in quite a few calories through drink and still feel hungry. If we ate the same number of calories, we'd feel full.
Ideally, children should drink only water and low-fat, unsweetened milk. Some studies suggest that artificially sweetened drinks, while lower in calories, can lead to overeating. They might fuel a sweet tooth. We do think that artificial sweeteners are safe, but we are probably better off without them.
Sports drinks are rarely necessary. They might make sense if you are going to be involved in a long, vigorous activity, such as a marathon or a day-long tournament. But for your average athletic competition or activity, water is fine. Even 100% juice, which is better than a sugar-sweetened drink, should be limited to once a day.
What Can I Expect Looking to the Future?
As I always say whenever I write about nutrition or obesity, what we can expect if we don't make some big changes is more obese children and adults. Two-thirds of U.S. adults and one-third of U.S. children are overweight or obese. This has huge implications, not just for all of those people, but for us as a country.
That's why we need to pay attention to these studies. Getting rid of sugar-sweetened drinks isn't the cure for obesity. But it would help. And we need to do anything and everything that would help.