Posted Aug 31, 2009
The human body does not absorb an important antioxidant from tomatoes effectively unless they have been cooked. New Zealand researchers have confirmed.
Scientists from Plant and Food Research created a model of the digestive system by subjecting foods to an acidic environment similar to the stomach, then deacidifying and exposing them to intestinal enzymes. Three-quarters of tomato antioxidants were released in a form that would be absorbed in the body, but just 4% of lycopene became available unless the tomato had been cooked first.
“Tomatoes are the richest source of lycopene in the human diet, as well as containing other antioxidants essential for health,” says nutritional biochemist Carolyn Lister. “However, the human digestive tract is not able to release the majority of lycopene from raw tomatoes, so only a small amount would be made available for the body to use.
“Processing tomatoes has been shown to make lycopene more bioavailable, so as well as eating raw tomatoes for their nutritional value we should eat tomato sauces to get the goodness of the lycopene,” Lister says.
The low bioavailability of lycopene in raw tomatoes has been known for a while, but Lister hopes her research will “reinforce the message”. She notes: “There are still a lot of people who assume eating raw food must be better”.
Lister has yet to quantify how much cooking releases quantities of lycopene, but doubts that a quick stir fry will match the use of tomato sauce. She says there is a healthy balance between releasing the antioxidant and damaging it. “If a sauce is still red it is an indication the lycopene and other antioxidants are still there, but ir it has gone brown they have started to degrade.”
Some rarely cooked red fruits such as watermelons and guavas are also rich in lycopene. Lister says the research has vet to be done to establish the bioavailability of lycopene in these fruits, and it may sometimes be higher than raw tomatoes but “it’s probably not as good” as tomato sauce.
Benefits from lycopene have been proposed as one explanation lor an association between high tomato consumption and low cancer risk, but the theory is tar horn universally supported.
Date: Aug 24, 2009