Grapefruit flavonoid naringenin helps muscles' glucose uptake
Naringenin is a flavonoid found in grapefruit. Most readers of ergo-log will recognise naringenin as the substance that sabotages glucose uptake in fat cells. [Biochem Biophys Res Commun. 2003 May 30;305(2):229-34.] That same naringenin actually stimulates the uptake of glucose in muscle cells, write health scientists from Brock University, Canada, in Biochemical and Biophysical Research Communications. [We read every number. Religiously. We are fans.]
The diagram shows the structure of naringenin, which is remarkably similar to that of quercetin. Remove 2 hydroxyl groups from quercetin and you've got naringenin. Because naringenin's structure resembles that of resveratrol, and because the researchers had previously discovered that resveratrol induces muscle cells to absorb more glucose [Biochem Biophys Res Commun. 2008 Sep 12; 374(1): 117-22.] the Canadians wanted to know whether naringenin does the same. The researchers are looking for ways of lessening the damaging effects of diabetes-2 through diet.
The Canadians exposed young and fully-grown muscles cells of rats to naringenin in test tubes. Young muscle cells did not react, adult ones did. This indicates that naringenin enhances the activity of GLUT4, a glucose transporter. Fully-grown muscle cells synthesise it; young muscles cells don't.
The figure below shows that as the naringenin concentration rises, the muscle cells take up more glucose. The figure underneath shows that the glucose uptake rises, the longer the exposure to 75 micromols naringenin.
The third figure shows that 75 micromols naringenin boosts the glucose uptake in the presence of insulin. The bottom figure shows how naringenin works: it boosts the amount of active AMPK. AMPK is an enzyme that becomes active when muscle cells have exhausted their fuel supply. It starts up mechanisms which enable the muscle cell to take up more fuels from the bloodstream.
A grapefruit contains about 50 mg naringenin per 100g. The concentration of naringenin in people who have eaten grapefruit varies from 0.7 to 14.8 micromol. So it's possible that the naringenin concentrations used in this study are found in some people in their normal everyday life.
Less energy going to your fat cells and more energy going to your muscles: insulin boosters that inhibit fat cells are always more than interesting.
Biochem Biophys Res Commun. 2010 Jul 23;398(2):178-83.
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