The effect of the load, the type (soy or whey protein) and the form (intact or hydrolysed) of proteins incorporated in a fruit beverage, produced industrially, on insulin and glucose responses in 25 healthy men was investigated in a double-blind cross-over trial. The results obtained suggested that all beverages containing 6% (w/v) protein increased insulin response above values observed for the control beverage, and decreased plasma glucose level under the values observed for the control beverage. These effects were not observed after the ingestion of the beverage enriched with 2.66% of whey protein isolate (WPI). However, the same load (6%) of a vegetable and animal protein, or an isolate and a hydrolysate, did not induce the same physiological effect. Indeed, only the 6% WPI protein-enriched beverage induced a significantly higher C-peptide area under the curve than the other beverages and consequently, can be classified as a functional food.