Insulin-like biological activity of culinary and medicinal plant aqueous extracts in vitro

To evaluate the possible effects on insulin function, 49 herb, spice, and m edicinal plant extracts were tested in the insulin-dependent utilization of glucose using a rat epididymal adipocyte assay. Cinnamon was the most bioa ctive product followed by witch hazel, green and black teas, allspice, bay leaves, nutmeg, cloves, mushrooms, and brewer's yeast. The glucose oxidatio n enhancing bioactivity was lost from cinnamon, tea, witch hazel, cloves, b ay leaf and allspice by poly-vinylpyrrolidone) (PVP) treatment, indicating that the active phytochemicals are likely to be phenolic in nature. The act ivity of sage, mushrooms, and brewers's yeast was not removed by PVP. Some products such as Korean ginseng, flaxseed meal, and basil have been reporte d to be effective antidiabetic agents; however, they were only marginally a ctive in our assay. Our technique measures direct stimulation of cellular g lucose metabolism, so it may be that the active phytochemicals in these pla nts improve glucose metabolism via other mechanisms or that this in vitro s creening is not a reliable predictor of hypoglycemic effects in vivo for so me products. In summary, the positive effects of specific plant extracts on insulin activity suggest a possible role of these plants in improving gluc ose and insulin metabolism.