A process for the bioactivity guided fractionation of the rhizomes of Cyperus rotundus to obtain anti-adipogenic/anti-obesity compositions comprising A. scirpusin A and scirpusin B represented by STR#1 and STR#2 and B. piceatannol and its dimers scirpusin A and scirpusin B represented by STR#1 and STR#2 respectively, said process comprising the steps of: a) Drying the rhizomes of Cyperus rotundus and pulverizing the same to form a coarse powder; b) Extracting the powder of step a) with 3 volumes of hexane followed by heating, reflux for 3 hours and filtering to obtain the hexane soluble fraction and spent material; c) Extracting the spent material of step b) with 3 volumes of methanol followed by heating, reflux for 3 hours and filtering to obtain the methanol soluble active fraction and spent material; d) Solubilizing the methanol soluble active fraction of step c) in aqueous methanol and successively partitioning with chloroform (CHCl 3), Ethyl acetate (EtOAc) and methanol to obtain the chloroform layer, ethyl acetate layer and the aqueous methanol layer respectively; e) Subjecting the chloroform layer, ethyl acetate layer and the aqueous methanol layer to further bioactivity guided fractionation, wherein the bioactivity parameter is the ability of the chloroform layer, ethyl acetate layer and the aqueous methanol layer to inhibit adipogenesis in 3T3-L1 mouse adipocytes (mammalian adipocytes); f) Calculating the IC 50 (μg/ml) values for adipogenesis inhibition exemplified by chloroform layer, ethyl acetate layer and the aqueous methanol layer (0, 9.39 and 66.42 respectively); g) Fractionation of the ethyl acetate layer using column fractionation to identify the bioactivity (adipogenesis inhibition) biomarker, said fractionation includes the step where fractions are eluted with increasing polarity of methanol: chloroform to yield sub-fractions of the ethyl acetate layer (fraction); h) Subjecting the sub fractions of step g) for bioactivity (anti-adipogenesis) analysis; i) Identifying the most bioactive sub fractions of step h) and subjecting the same to LC-MS analysis to identify the bioactive principles scirpusin A and scirpusin B; j) Subjecting sub fractions of step g) through the preparative HPLC to obtain purified dimer and subjecting the same to High Resolution Mass Spectroscopy (HRMS), liquid chromatography-mass spectrometry (LC-MS/MS) and Nuclear Magnetic Resonance Spectroscopy to confirm the mass and structures of scirpusin bioactive principles. a) Drying the rhizomes of Cyperus rotundus and pulverizing the same to form a coarse powder; b) Extracting the powder of step a) with 3 volumes of hexane followed by heating, reflux for 3 hours and filtering to obtain the hexane soluble fraction and spent material; c) Extracting the spent material of step b) with 3 volumes of methanol followed by heating, reflux for 3 hours and filtering to obtain the methanol soluble active fraction and spent material; d) Solubilizing the methanol soluble active fraction of step c) in aqueous methanol and successively partitioning with chloroform (CHCl 3), Ethyl acetate (EtOAc) and methanol to obtain the chloroform layer, ethyl acetate layer and the aqueous methanol layer respectively; e) Subjecting the chloroform layer, ethyl acetate layer and the aqueous methanol layer to further bioactivity guided fractionation, wherein the bioactivity parameter is the ability of the chloroform layer, ethyl acetate layer and the aqueous methanol layer to inhibit adipogenesis in 3T3-L1 mouse adipocytes (mammalian adipocytes); f) Calculating the IC 50 (μg/ml) values for adipogenesis inhibition exemplified by chloroform layer, ethyl acetate layer and the aqueous methanol layer (0, 9.39 and 66.42 respectively); g) Fractionation of the ethyl acetate layer using column fractionation to identify the bioactivity (adipogenesis inhibition) biomarker, said fractionation includes the step where fractions are eluted with increasing polarity of methanol: chloroform to yield sub-fractions of the ethyl acetate layer (fraction); h) Subjecting the sub fractions of step g) for bioactivity (anti-adipogenesis) analysis; i) Identifying the most bioactive sub fractions of step h) and subjecting the same to LC-MS analysis to identify the bioactive principles scirpusin A and scirpusin B; j) Subjecting sub fractions of step g) through the preparative HPLC to obtain purified dimer and subjecting the same to High Resolution Mass Spectroscopy (HRMS), liquid chromatography-mass spectrometry (LC-MS/MS) and Nuclear Magnetic Resonance Spectroscopy to confirm the mass and structures of scirpusin bioactive principles.