Naringin is a flavonoid that gives grapefruit its distinct bitter flavor.

Research shows that naringin acts as an antioxidant and may help to stabilize blood sugar. Because naringin alters enzymatic activity in the intestines it interferes with the metabolism of a number of pharmaceutical drugs.

References

Jung UJ, Lee MK, Park YB, Kang MA, Choi MS.Effect of citrus flavonoids on lipid metabolism and glucose-regulating enzyme mRNA levels in type-2 diabetic mice.Int J Biochem Cell Biol. 2006 Jul;38(7):1134-45. Epub 2006 Jan 6. Ho PC, Saville DJ, Wanwimolruk S. Inhibition of human CYP3A4 activity by grapefruit flavonoids, furanocoumarins and related compounds. Journal of Pharmacy and Pharmaceutical Sciences, 2001, 4, 217-227. Fuhr U, Klittich K, Staib AH. Inhibitory effect of grapefruit juice and its bitter principal, naringenin, on CYP1A2 dependent metabolism of caffeine in man. British Journal of Clinical Pharmacology, 1993, 35, 431-436. Jung UJ, Lee MK, Jeong KS, Choi MS.The hypoglycemic effects of hesperidin and naringin are partly mediated by hepatic glucose-regulating enzymes in C57BL/KsJ-db/db mice.Nutr. 2004 Oct;134(10):2499-503. Kanno S, Shouji A, Asou K, Ishikawa M.Effects of naringin on hydrogen peroxide-induced cytotoxicity and apoptosis in P388 cells.J Pharmacol Sci. 2003 Jun;92(2):166-70.