A team of scientists from South Korea reporting in the Archives of Pharmacology has investigated green tea’s reputed effects on weight loss and type 2 diabetes.
Green tea extract (GTE) is regarded by some as a herbal remedy for these conditions. When present in the intestinal lumen after oral ingestion, the gallated catechins (GCs) of GTE have been shown to inhibit intestinal glucose uptake by inhibiting the type 1 sodium-dependent glucose transporter (SGLT1). In addition, GCs have also been shown to inhibit the intestinal absorption of lipids. However, GCs have not yet been adapted as a therapeutic drug for type 2 diabetes, whereas α-glucosidase inhibitors have been.
The Korean team did their work based on the assumption that the gallated catechins weaken intestinal glucose and lipid absorption, while enhancing insulin resistance by inhibiting cellular glucose uptake in various tissues. Hence they attempted to block the intestinal absorption of GCs and observe whether GTE containing the nonabsorbable GCs could ameliorate body weight (BW) gain and glucose intolerance in db/db (a model of obesity, diabetes, and dyslipidemia wherein leptin receptor activity is deficient) and high-fat diet mice. They found that GTE mixed with meals did not have any ameliorating effects on BW gain and glucose intolerance. However, the administration of GTE plus a synthetic chemical (PEG 3350, a polyethylene glycol) significantly reduced BW gain, insulin resistance, and glucose intolerance, without affecting food intake and appetite. The effect was comparable to that of the α-glucosidase inhibitors used in treatment for type 2 diabetes.
They conclude that prolonging the action of GCs from green tea in the intestinal lumen and blocking their entry into the circulation may allow green tea extract to be used as a prevention and treatment for both obesity and obesity-induced type 2 diabetes.