An increasing amount of fructose in the diet is suggested to play a causal role in the pathogenesis of the metabolic syndrome, type 2 diabetes and fatty liver. Our aim was to investigate and compare the effects of very high fructose and very high glucose in hyperenergetic diets on glucose and lipid metabolism and on fat depots in healthy humans. We conducted an exploratory, prospective, randomised, single-blinded, intervention trial. Participants in addition to a balanced weight-maintaining diet received 150 g of fructose or glucose/d for 4 weeks. Insulin sensitivity was estimated from oral glucose tolerance tests. Visceral and subcutaneous abdominal fat was determined with MRI. Liver fat and intramyocellular lipids of the tibialis anterior muscle were measured with (1)H magnetic resonance spectroscopy. A total of twenty healthy subjects (fructose group n 10 and glucose group n 10; twelve males and eight females) completed the study. They had a mean age of 30·5 (SEM 2·0) years and a mean BMI of 25·9 (SEM 0·5) kg/m(2). Insulin sensitivity appeared to decrease both in the fructose and glucose groups. TAG markedly increased in the fructose group. No strong alterations or treatment effects were found for liver fat, visceral fat, subcutaneous abdominal fat and intramyocellular lipids of the tibialis anterior muscle. In conclusion, the effects of very high fructose and very high glucose in hyperenergetic diets on glucose metabolism and body fat composition were not different in the healthy participants of the present study. However, elevation of plasma TAG seemed to be fructose-specific.