A new study has reported that sulforaphane, a chemopreventive compound found in cruciferous vegetables such as broccoli, broccoli sprouts, cabbage, cauliflower, kale, and watercress is absorbed during digestion of cooked cruciferous vegetables and therefore biologically available. The study was designed to test the theory that glucoraphanin in cooked cruciferous vegetables is hydrolyzed by bacteria in the lower gut to produce the bioactive isothiocyanate sulforaphane in the absence of the plant enzyme myrosinase (part of the plant defense against herbivores which acts when plants are crushed or chewed and which is disabled when such plants are cooked). In the study, digestion was simulated in rats and found to cause no loss of glucoraphanin, confirming that glucoraphanin is not destroyed by digestive enzymes during passage through the digestive tract and is able to reach the rat cecum (a pouch at the beginning of the large intestine) intact. Introduction of glucoraphanin directly into the cecum resulted in appearance of isothiocyanates in the mesenteric vein, which flows from the gut to the liver, within two hours.

Incubation of cecal bacteria from rats with glucoraphanin in the laboratory demonstrated that metabolism by microbiota in experimental conditions does not mirror metabolism in the actual conditions found within the body. The authors comment that the study is the first to report direct evidence that sulforaphane is able to cross the cecal enterocyte for systemic absorption. In a separate interview, study author Elizabeth Jeffery, professor of nutrition at the University of Illinois, commented that the study findings are reassuring "because many people overcook their broccoli, unwittingly destroying the plant enzyme that gives us sulforaphane. Now we know the microbiota in our digestive tract can salvage some of this important cancer-preventive agent even if that happens."