(Inside Science) -- Elite athletes down sports drink to help them reach new heights of performance. But for the average young person, these "health drinks" may cause them to reach new highs -- on the bathroom scale.
A new study published in the journal Obesity suggests that young people who consume one or more sports drinks each day gained more weight over a three year period than classmates who chose other beverages.
"Not just children, but many adults use them who don't need them," said Nancy Rehrer, an exercise metabolism researcher at Otago University in Dunedin, New Zealand, who was not involved in the study. "Because sports drinks can be a very beneficial part of a very active lifestyle, I guess they're seen as a healthy alternative and that's probably a misrepresentation."
Sports drinks were designed to rehydrate hardworking athletes and to replace salts and sugars that they use or lose during exercise. The sugars in sports drinks replenish the energy stores in the muscles and liver, which are depleted during vigorous exercise. The salt replaces the sodium lost through sweat. Both ingredients help cells in the intestines to absorb fluid more quickly than water alone so the athlete can rehydrate and recover faster.
Though the average person gets more than enough calories from their meals, high-performance athletes such as Tour de France cyclists, struggle to consume enough energy through solid food to power their muscles through the grueling kilometers packed with punishing hills, explained Rehrer. Athletes who consume too much water during events also risk developing deadly hyponatremia -- a condition where they dilute the sodium levels in the blood, and can’t excrete the excess water. Sports drinks can improve an athlete's performance in these situations.
"They were developed for people engaging in at least 60 minutes of continuous activity in high heat - so think about football practice in Florida in the summer," said study leader Alison Field, an epidemiologist at Harvard Medical School in Boston, Massachusetts.
Field is also a long-distance runner who admits to drinking the occasional sports drink, but only if she runs for at least an hour. A single 32 ounce bottle will last her through an entire marathon, supplemented with water and energy gels.
Of course, people need to rehydrate during exercise, especially when sweating heavily. To prevent dehydration, the American College of Sports Medicine recommends that athletes should drink enough fluids that they lose less than 2% of their body weight. When exercising for fun or weight loss, water is an ideal way to rehydrate, agreed both Rehrer and Field.
Sports drink consumption is up in the United States. Regular soda is still the most popular sugary beverage, but sales have declined over the past decade. One study found that one out of every four beverages that young people consume is now a sports drink. Soda and other sugar-laden drinks have received increasing attention for their connection to weight gain and obesity in young adults, but the role of sports drinks on weight had not been examined.
Field and her colleagues analyzed data from the Growing Up Today II study, a survey of the eating and exercise habits of children aged nine to 14. The survey began in 2004, and the researchers sent follow-up questionnaires every two or three years.
For each participant, the researchers calculated the body mass index, which is an estimate of body fat percentage based on a person's height and weight, and compared it to their drinking habits. They found that for each sports drink that adolescents drank per day, they gained 0.3 BMI units over the three-year period. This weight gain corresponds to about one or two pounds per drink for an average teenager.
This bump on the scale might seem insignificant, but the increase is above and beyond the weight gain caused by other food and drink choices. The excess weight is especially concerning for the large number of adolescents who are already overweight or obese. "People have assumed that sports drinks are a much better option than soda, or that they're a healthy part of someone's life," said Field. She credits the beverage industry's brilliant marketing. "They have really coupled the image of sports drinks with a very healthy lifestyle and with professional athletes."
Ounce for ounce, sports drinks have less sugar than soda. But when packaged in extra-large bottles with multiple servings, they still pack a sugary punch.
"It's not much different from any other source of sugar," said Rehrer. Still, she hates to see sports drinks demonized. "We can improve endurance performance by giving some carbohydrate and some extra fluid," but these drinks should be reserved for intense and prolonged exertion, she said.
One study estimates that only eight percent of young people exercise for at least 60 minutes each day, indicating that the number of students who need sports drinks frequently is very low.
A quart-sized bottle also contains about one third of the daily recommended level of sodium. Because sodium -- mostly in the form of salt -- is also prominent in canned soups and other processed foods, most Americans consume far too much. In some people, excess sodium has been linked to elevated blood pressure, heart attacks and strokes.
In 2006, the American Beverage Association agreed not to sell regular soda in schools, but diet soda, flavored water and sports drinks are still available in vending machines. During the next year, the U.S. Department of Agriculture will roll out its Smart Snacks in School regulations which will limit the calories allowed in school drink options, which will eliminate many sports drinks.
"In the ideal world everyone would transition to drinking water, but it's unlikely to happen," said Field.
Patricia Waldron (@patriciawaldron) is a news intern at Inside Science.