A mixture of extracts of black and green teas and mulberry leaf did not reduce weight gain in rats fed a high-fat diet.

Tea extracts are used in many over-the-counter preparations claiming to promote weight loss. The rationale for this usage includes reports that green tea extract increases thermogenesis, and extracts of green and black tea and mulberry leaf inhibit the digestion/absorption of carbohydrate and fat. The investigators in this study tested the potential of increasing doses of a mixture of three extracts (50-percent black tea, 20-percent green tea, and 30-percent mulberry) to induce weight loss, steatorrhea, and blood lipid alterations in rats ingesting a high-fat diet, ad lib. The mixture was incorporated into chow in quantities of 0.5-, 3.0-, and 6.0 percent by weight; a control group received only chow. Food intake and weight were monitored daily, and quantitative fecal fat measurements were obtained weekly for four weeks. The 3.0- and 6.0-percent chows significantly increased fecal fat excretion to 15 percent of dietary fat intake (controls: 5 percent); however, no significant reduction in weight gain was observed. After four weeks of treatment, the 3.0- and 6.0-percent dosages were associated with significant reductions in serum triglycerides and increases in high-density lipoprotein (HDL) cholesterol. However, these chow concentrations were associated with significant increases in serum ALT, and the 6.0-percent chow markedly increased serum alkaline phosphatase. This study does not provide support for the utility of this combination of black tea, green tea, and mulberry extracts in weight-loss regimens and indicates that high doses of this extract combination may be hepatotoxic.

An extract of black, green, and mulberry teas causes malabsorption of carbohydrate but not of triacylglycerol in healthy volunteers.

BACKGROUND: In vitro studies suggest that extracts of black, green, and mulberry teas could interfere with carbohydrate and triacylglycerol absorption via their ability to inhibit alpha-amylase, alpha-glucosidase, sodium-glucose transporters, and pancreatic lipase. OBJECTIVE: We measured breath hydrogen and 13CO2 to investigate the ability of an extract of black, green, and mulberry tea leaves to induce malabsorption of carbohydrate and triacylglycerol in healthy volunteers. DESIGN: In a crossover design, healthy adult volunteers randomly ingested test meals with a placebo beverage or a preparation containing an extract of black (0.1 g), green (0.1 g), and mulberry (1.0 g) teas. One test meal contained 50 g carbohydrate as white rice, 10 g butter, and 0.2 g [13C]triolein, and the beverages contained 10 g sucrose. The calorie content of the second test meal consisted entirely of lipid (30 g olive oil and 0.2 g [13C]triolein). Breath-hydrogen and 13CO2 concentrations were assessed hourly for 8 h, and symptoms were rated on a linear scale. RESULTS: With the carbohydrate-containing meal, the tea extract resulted in a highly significant increase in breath-hydrogen concentrations, which indicated appreciable carbohydrate malabsorption. A comparison of hydrogen excretion after the carbohydrate-containing meal with that after the nonabsorbable disaccharide lactulose suggested that the tea extract induced malabsorption of 25% of the carbohydrate. The tea extract did not cause triacylglycerol malabsorption or any significant increase in symptoms. CONCLUSION: This study provides the basis for additional experiments to determine whether the tea extract has clinical utility for the treatment of obesity or diabetes.