They say the extract may be helpful in humans for preventing diet-induced obesity and perhaps even metabolic syndrome.
The team from Kirin Brewery and Tokyo-based medical institutes fed two strains of mice commonly used as an animal model for type 2 diabetes with a standard or high-fat diet containing isohumulones, the compounds that make up isomerized hop extract.
"Supplementation of high-fat-containing chow with hop extract reduced body weight gain and improved glucose tolerance in our experimental mice," said the researchers in this month's issue of the International Journal of Obesity (vol 29, issue 991-997).
A reduction in body weight gain was also observed in the mice fed a standard diet with added hop extract.
In further tests on Wistar rats, the researchers found that those fed a high-fat diet containing hop extract for 15 days showed reduced plasma triacylglycerol levels and an increase in their faecal lipid excretion.
The pancreatic lipase activity was inhibited in these rats and the supplement also suppressed raised triacylglycerol levels after administration of a lipid emulsion.
The hop extract-fed mice showed an increased expression in their lipid oxidation genes and a decreased expression in genes involved in triacylglycerol biosynthesis.
The authors conclude that the hop extract may inhibit intestinal dietary fat absorption. It could also alter lipid metabolism, explaining, at least in part, the beneficial effects on body weight gain.