Using urinary sugars as a biomarker of consumption, we have previously shown that obese people consume significantly more sugars than individuals of normal weight. However, there is concern that recovery of this biomarker may differ between normal weight and obese individuals. A total of 19 subjects, divided into two groups according to their body mass index (BMI) (normal weight BMI < or = 25 kg/m(2), n=10; obese BMI > or = 30 kg/m(2), n=9), participated in a randomized crossover dietary intervention study of three diets providing 13, 30 and 50% of energy from sugars for 4 days each while living in a volunteer suite. The mean urinary sucrose and fructose excretions in 24-h urine increased with increasing sugar consumption over the three dietary periods in both BMI groups and were significantly different between the diets (P < 0.01). There was no significant interaction effect of BMI class on the mean urinary excretions of these sugars with different sugar intakes, either as absolute values or expressed as a percentage of total sugar intake. In conclusion, BMI does not affect the validity of sucrose and fructose excretions in 24-h urine collections used as biomarkers to estimate total sugar consumption.