A mixture of extracts of black and green teas and mulberry leaf did not reduce weight gain in rats fed a high-fat diet by Elizabeth Fallon, Litao Zho

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%); 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. (Altern Med Rev 2007; 12(4):43-49)

Introduction

At least 402 different dietary supplements for the purpose of weight reduction are sold in the United States, (1) a sizeable portion of which contain various teas or tea extracts. To date, studies designed to demonstrate tea-induced weight loss have yielded variable results. (2-5)

The scientific basis for the use of tea for weight control includes reports that green and black tea extracts increase thermogenesis, (6-8) black tea inhibits fat digestion, (9,10) and green tea and mulberry leaf extracts inhibit the digestion and absorption of carbohydrate. (11-18) The present study hypothesized that a combination of these extracts would reduce weight gain in rats fed a high-fat diet. Varying dosages of a mixture of extracts of green tea, black tea, and mulberry leaf were added to chow, and potentially beneficial effects on weight loss, fecal fat excretion, and blood lipids were assessed, as were deleterious effects on hepatic and renal function.

Material and Methods

Extracts and Chow

The extract mixture was provided by NatureGen, Inc. (San Diego, CA) and consisted, by weight, of extracts of black tea (50%), green tea (20%) and mulberry (Morus alba) leaf (30%). The extracts were produced via repeated extraction of the dried leaves with a water/ethanol mixture, followed by evaporation to dryness. The mixture was incorporated into pellets made from a high-fat chow supplied by Harlan-Teklad Custom Research Diets (Madison, WI) (Table 1). Milk fat comprised about 43 percent of the chow calories, while carbohydrate (primarily corn starch) and protein (casein) provided about 42- and 15 percent of total calories (4.3-4.5 Kcal/g), respectively.

Subjects

Twenty male, Sprague-Dawley (Harlan; Indianapolis, IN) rats with initial weights of approximately 250 g were used. The rats were divided into four groups of five and provided with ad lib access to water and high-fat chow into which had been incorporated (by weight) 0.5-, 3.0-, and 6.0 percent of the mixture of extracts; a control group received chow without any of the extract mixture. The black tea dosages were selected to bracket the quantity required to yield an in vitro inhibition of pancreatic lipase similar to that of Orlistat[R], a commercially available lipase inhibitor. The green tea and mulberry dosages were approximately five times greater (per unit body surface area) than the dosages previously shown to inhibit carbohydrate absorption in humans. (19,20) The study was approved by the Animal Studies Subcommittee of the Minneapolis Veterans Affairs Medical Center.

Measurements

Food intake was assessed daily and individual body weights were obtained weekly. Fecal fat was measured weekly by housing the rats in individual wire screen bottom cages to minimize coprophagy, with measurements after one, two, and three weeks determined on 24-hour fecal collections. A three-day fecal collection was obtained for the measurements at four weeks. Fecal fat was determined using minor modifications of a standard gravimetric technique. (21) Total fecal collection was added to pre-weighed polypropylene tubes. After the weight was determined, a recorded volume of water was added as needed to provide a smooth homogenate via a blender. Three grams of homogenate was transferred to polypropylene tubes with 1 drop concentrated HCl, 5 mL ethanol, and 10 mL hexane. The tubes were shaken for 10 minutes and centrifuged for five minutes. The hexane layer was transferred to pre-weighed glass vials. This extraction procedure was repeated with an additional 10 mL of hexane. The extracts were evaporated to dryness over a steam bath and stored overnight in a desiccator. The dry weights of the two extracts were added to obtain total fecal fat.