The invention relates to the method for decreasing postprandial glucose excursion in a mammal in need thereof comprising a step of administering to said mammal an effective amount of water comprising from 99.76 to 99.99 molecular % of isotopologue .sup.1H.sub.20 at 0 to 240 min from the start of ingestion of a meal. Preferably, the effective amount water comprising from 99.76 to 99.99 molecular % of isotopologue .sup.1H.sub.2.sup.160 is administered orally. Preferably, the effective amount of the water comprising from about 99.76 to about 99.99 molecular % of isotopologue .sup.1H.sub.2.sup.160 is 0.1 to 20 g/kg body weight of a mammal. Further, invention relates to the medical food for decreasing postprandial glucose excursion in a mammal in need thereof which comprises water comprising from about 99.76 to about 99.99 molecular % of isotopologue .sup.1H.sub.2.sup.160. Further, invention relates to use of water comprising from about 99.76 to about 99.99 molecular % of isotopologue .sup.1H.sub.2.sup.160 for the manufacture of a medical food for decreasing postprandial glucose excursion in a mammal in need thereof. Preferably, the mammal is human.