- Control: volunteers will be fed a weight-maintenance diet containg 5% sugars, 45% starch, 35% fat and 15% protein during 6 days (day 1-6); On day 7, their plasma metabolites and hormones concentrations will be monitored over 10 hours during which they will receive a breakfast and a lunch with no added sugar; on day 8, they will have a 75g oral glucose + 375 mg 13C-labelled glucose tolerance test, and their plasma glucose and insulin concentrations will be monitored over 4 hours; glucose kinetics will be measured by 6,6 deuterated glucose