Carotenoids, and their oxidised metabolites xanthophylls, are a heterogenous group of phytonutrients responsible for many of the orange, yellow and red colours found in plants. Examples of carotenoids include β-carotene and α-carotene in carrots and lycopene in tomatoes. Carotenoids are bioavailable in humans and animals, where they may confer particular health benefits. In particular, carotenoids have been researched for their ability to prevent cancer. This anti-cancer related activity may relate to the ability of carotenoids to act as free radical scavengers. The antioxidant ability of carotenoids have been shown to reduce the effects of oxidative stress in humans, and in animals and cell culture models. Increasing intakes of foods containing carotenoids may reduce the risk of developing certain types of cancer significantly. In particular, certain carotenoids may have effects against specific types of cancer and this may relate to the way they accumulate in specific tissues.
Tomatoes are a rich source of the carotenoid lycopene. This is largely responsible for the red colour of tomatoes. Lycopene is not able to be converted into vitamin A in humans as with other carotenoids including β-carotene. However, the lack of provitamin A activity does not mean that lycopene does not have significant health effects. Lycopene is an antioxidant and may significantly reduce the risk of prostate cancer. Good sources of of lycopene are foods containing concentrated forms of tomatoes, and this include tomato juice and tomato sauce. Like all carotenoids, lycopene is best absorbed in meals containing fat, and this relates to the lipid soluble nature of carotenoids.
For example, tomatoes are a rich source of lycopene. Lycopene has been shown to accumulate in the prostate and here it may confer antioxidant protection, which may in turn inhibit the growth of cancer cells. A number of studies have shown inverse associations between lycopene intake and the risk of prostate cancer. One group of researchers investigated the association between tomato consumption over a 23 year period in a large group of men. The results showed that there was a significant inverse association between tomato sauce intake and prostate cancer, and this association became stronger as cumulative tomato sauce intake increased. Those subjects with more than 2 servings per week of tomato sauce had a significantly lower risk of prostate cancer compared with those consuming less than 1 serving per week. The researchers also showed that tomato sauce was protective of only one type of prostate cancer, but lycopene intake was protective of more than one type suggesting other factors may modify the association.
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