The present invention relates generally to methods and related compositions using flavonoids and/or indanes extracted from the stems and leaves of C. quadrangularis to reduce weight and inhibit lipase, .alpha.-amylase and .alpha.-glucosidase activity in mammals. By example and not by way of limitation, embodiments of the present disclosure, a composition and related methods for reducing body weight and/or inhibiting any combination of lipase, .alpha.-amylase and .alpha.-glucosidase is provided. The composition contains an effective amount of one or more flavonoids or indanes selected from 3-O-rhamnopyranosylkaempferol, 3-(4-hydroxybenzylidene)-2-(2,5-dihydroxyphenyl)-1-(4-hydroxyphenyl)indan- e-4,6-diol, quercitrin, rhamnitrin, rhamnocitrin, quercitrin-3-O''-acetate and parthenocissin A.