Increased consumption of so-called free sugars, including additives to foods and those naturally present in honey, syrups and fruit juices, led to an average gain of 0.8kg (1.8 pounds) in body weight in adults, researchers at the University of Otago in New Zealand found in a review of 71 studies. Limiting the analysis to studies lasting longer than eight weeks, weight gain was 2.7kg, they said.
The WHO commissioned the review in preparation for updating its 2003 recommendation that free sugar be limited to less than 10% of energy intake. The study adds to a debate over public policy aimed at curbing the obesity epidemic and related diseases, including New York City's decision to restrict sales of large-sized sugary soft drinks.
"When considering the rapid weight gain that occurs after an increased intake of sugars, it seems reasonable to conclude that advice relating to sugars intake is a relevant component of a strategy to reduce the high risk of overweight and obesity in most countries," the authors said in a paper published in the British Medical Journal.
Cutting consumption of sugars led to an average 0.8kg reduction in weight in adults, according to five studies that ranged from 10 weeks to eight months, the authors said. Among studies in children, comparison of varying levels of consumption suggested a "significantly increased risk" of being overweight associated with higher intakes, they said.
"This review clearly indicates the positive association, which I think is quite striking, given that no such systematic reviews have been conducted so far," Chizuru Nishida, a coordinator in the WHO's Department of Nutrition for Health and Development in Geneva, said in an interview. The study defends the current WHO guidelines that have been criticized as having no scientific basis, she said.
The WHO has commissioned a second study, to be published sometime in the next few months, looking at sugars and tooth decay and will consider both analyses in its updated recommendation, Nishida said.
"Reducing the amount of sugar consumed in drinks deserves special attention because of the strength of the evidence and the ease with which excessive sugar is consumed in this form," said Walter Willett, a professor at the Harvard School of Public Health, and David Ludwig, a professor at the Boston Children's Hospital, in an editorial accompanying the study. "But questions remain. What is a desirable limit?"
In September, New York City's Board of Health approved Mayor Michael Bloomberg's plan to restrict sales of sugary soft drinks to no more than 16oz. (450g) a cup. They rejected arguments from Coca-Cola Co., PepsiCo Inc. and restaurant companies whose coalition says the issue is about consumers' freedom to choose. The mayor is founder and majority owner of Bloomberg News parent Bloomberg LP.
Recent efforts to tax soft drinks have foundered in at least 30 U.S. states. The federal government rejected an attempt in 2011 to bar purchases of sugared drinks with food stamps.
In Europe, a sugar tax in Denmark was abandoned in November after a fat tax was criticized for raising prices and droving consumers to shop in neighboring countries like Germany.
Soft-drink makers say their products contribute 7% of calories to the average daily diet in the U.S. and 3% in Europe, too little to be the cause of obesity.
Weight gain can be slowed by paying attention to the amount of calories consumed and burned through exercise, the American Beverage Association has said. Soda makers have offered smaller packages, labeled products with clearer calorie counts and agreed to stop selling sugary drinks in most schools.
In 2006, soft-drink manufacturers committed to abstaining from advertising in Europe to children under 12 on television, online and in print and to refrain from sales in primary schools, according to the Union of European Beverages Associations.
Coca-Cola started airing TV advertisements this week urging consumers to pay attention to calories of beverages, including its own, and noted its low- and zero-calorie products.
The WHO's 2003 report disregards evidence suggesting that refined carbohydrates have metabolic effects comparable to those of sugar, Willett and Ludwig said.
"Efforts to reduce sugar intake are appropriate, but they should form part of a broader effort to improve the quality of carbohydrates," they said. "Action should be taken at many levels, including education programs, improvements in food and drinks provided in schools and work sites, and supplemental nutrition programs for people with low incomes."