Controversies about sugars: results from systematic reviews and meta-analyses on obesity, cardiometabolic disease and diabetes
BACKGROUND The contribution of fructose consumption in Western diets to overweight and obesity in populations remains uncertain. PURPOSE To review the effects of fructose on body weight in controlled feeding trials. DATA SOURCES MEDLINE, EMBASE, CINAHL, and the Cochrane Library (through 18 November 2011). STUDY SELECTION At least 3 reviewers identified controlled feeding trials lasting 7 or more days that compared the effect on body weight of free fructose and nonfructose carbohydrate in diets providing similar calories (isocaloric trials) or of diets supplemented with free fructose to provide excess energy and usual or control diets (hypercaloric trials). Trials evaluating high-fructose corn syrup (42% to 55% free fructose) were excluded. DATA EXTRACTION The reviewers independently reviewed and extracted relevant data; disagreements were reconciled by consensus. The Heyland Methodological Quality Score was used to assess study quality. DATA SYNTHESIS Thirty-one isocaloric trials (637 participants) and 10 hypercaloric trials (119 participants) were included; studies tended to be small (<15 participants), short (<12 weeks), and of low quality. Fructose had no overall effect on body weight in isocaloric trials (mean difference, -0.14 kg [95% CI, -0.37 to 0.10 kg] for fructose compared with nonfructose carbohydrate). High doses of fructose in hypercaloric trials (+104 to 250 g/d, +18% to 97% of total daily energy intake) lead to significant increases in weight (mean difference, 0.53 kg [CI, 0.26 to 0.79 kg] with fructose). LIMITATIONS Most trials had methodological limitations and were of poor quality. The weight-increasing effect of fructose in hypercaloric trials may have been attributable to excess energy rather than fructose itself. CONCLUSION Fructose does not seem to cause weight gain when it is substituted for other carbohydrates in diets providing similar calories. Free fructose at high doses that provided excess calories modestly increased body weight, an effect that may be due to the extra calories rather than the fructose. PRIMARY FUNDING SOURCE Canadian Institutes of Health Research. (ClinicalTrials.gov registration number: NCT01363791).