Researchers found that people who consumed extra fructose baked into breads or sprinkled into drinks didn't gain any extra weight compared to those who had other types of carbohydrates instead – when they ate the same number of total calories.
On the other hand, when study participants supplemented a standard diet with extra calories in the form of straight fructose, they did gain weight.
"Fructose probably isn't any different than other sources of carbohydrates," said lead author Dr John Sievenpiper, a research fellow at St Michael's Hospital in Toronto.
Researchers have wondered whether there's something about fructose – typically found in fruits as well as baked goods and sugar-sweetened beverages – that makes people store fat and gain weight faster than other carbohydrates.
That's especially a concern because high-fructose corn syrup is a main ingredient in many common foods and drinks, including soda.
To see where the evidence stands, Sievenpiper and his colleagues looked back at studies that compared weight gain in people assigned to eat diets high in fructose or another carbohydrate instead, most commonly starch or glucose.
In 31 studies including 637 people, participants on both diets ate an equal number of calories, but those in the fructose groups got about 17 per cent of their calories from fructose, on average.
The studies included participants who were normal weight, overweight or obese, depending on the trial. Some of the study diets were designed to promote weight loss, while others aimed for maintenance or weight gain.
Over an average of four weeks, there was no difference in weight loss or gain between the different dieters, the researchers reported Monday in the Annals of Internal Medicine.
In the other 10 trials, with 119 participants, people assigned to the high-fructose groups ate the extra sugar on top of the normal calories fed to all participants – and they took in more than twice as much sugar as people in the equal-calorie studies.
In those trials, over an average of one and a half weeks on the diets, participants eating and drinking the extra sugar gained 1.2 pounds more than those in the comparison groups.
The results suggest it's not the fructose itself that causes weight gain, according to the researchers.
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