A Fraxinus excelsior seed extract that can be administered for therapeutic treatment of a subject, including a human, by blocking fat synthesis, activating PPAR-alpha, increasing hypoglycemic activity, reducing bodyweight, controlling fasting plasma insulin levels against hyperinsulinemia, and promoting insulin sensitivity and causing a beneficial acute insulinotropic effect. The Fraxinus excelsior seed extract includes, inter alia, an isolated compound (2S,3E,4S)2H-Pyran-4-acetic acid-3-ethylidene-2-[(6-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy]-3,4-dihydro-5-(methoxycarbonyl)methyl ester, commonly called excelside A, an isolated compound (2S,3E,4S) 2H-Pyran-4-acetic acid-3-ethylidene-2-[(6-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy]-3,4-dihydro-5-(methoxycarbonyl)2-(4-hydroxyphenyl)ethyl ester, commonly called excelside B, and the compounds GI5, GI3, nuzhenide, and oleoside dimethyl ester.