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'Carotenoids' is the term which describes the large range of more than 600 pigments which give many plants their characteristic red, orange or yellow colouring. Amongst those most commonly found in modern Western diets are alpha-carotene, beta-carotene, lutein, zeaxanthin, and lycopene.

Most attention has been paid to alpha-carotene and beta-carotene as these can be synthesized by the body to form vitamin A, which is one of the body's most powerful antioxidants, immune system boosters and infection fighters. Neither lutein, zeaxanthin nor lycopene are 'pro-vitamin A' active substances in this sense, but this should not be taken as detracting from their nutritional value in any way.

Indeed, the evidence now indicates that these lesser known carotenoids also function as valuable fat-soluble anti-oxidants within the body. Lycopene, in particular, is now even thought to be responsible for many of the anti-oxidant functions previously credited to beta-carotene. Research suggests that as a highly fat-soluble anti-oxidant, lycopene is particularly important in preventing free radical damage to the delicate but vital fatty structures of the body's cells, such as the membranes.

It also seems possible that lycopene may be at least as important as beta-carotene in protecting against the oxidation of Low Density Lipids (LDLs), the so-called 'bad cholesterol', which is now widely held to be a principal cause of atherosclerosis, or hardening of the arteries - the precursor of serious cardio-vascular diseases such as heart attack and stroke.

Like beta-carotene, lycopene has also generated much excitement as a potential weapon against cancer, probably because of its general anti-oxidant function, but also because of its proven role in keeping open the pathways between cells which are vital to allow the immune system to kill off cancer cells in the early stages of the disease.

In 1995 the Journal of the National Cancer Institute reported research suggesting a 45% reduction in rates of prostate cancer for men consuming a lycopene rich diet ' ie one containing considerable quantities of processed tomatoes. Other studies have since indicated a role for lycopene in combatting lung, stomach, colon and breast cancer; in protecting against cardiovascular disease, and as an immune system booster.

Unfortunately the consumption of a diet rich in lycopene presents practical problems which do not arise with the better known carotenoids, alpha and beta-carotene, because it is not nearly so widely available in common foodstuffs. It is lycopene which gives tomatoes their characteristic vivid red colour, and it is this fruit which is by far the richest source. But it is the processing and/or cooking of tomatoes which makes available far more lycopene than would be provided by the raw fruit.

So a cup of regular tomato paste may contain more than 75,000 mcg of lycopene, tomato puree more than 50,000, a regular can of tomato soup more than 25,000 and canned tomato juice perhaps 20,000. A serving of raw tomatoes, by contrast, will provide a mere 5,000. So rather than rely on raw tomatoes, unless you can consume truly heroic quantities, you'd do better to try a cup of canned mixed vegetable juice at around 23,000 mcg or even a slice of watermelon which may yield up to 13,000 mcg.

The above figures make it clear that processed tomatoes are the best source of significant dietary lycopene, but the problem with this from the point of view of the health purist is that the processing of tomatoes into soup, paste or puree commonly involves the addition of considerable amounts of salt and sugar ' just what your body doesn't need if you're seeking extra protection for your heart and circulatory system.

It also needs to be remembered when planning a lycopene rich diet that, as with other carotenes, the optimum absorption requires the presence of dietary fat. This is not so easy to achieve with tomatoes unless you're thinking about the rich kind of meat and tomato sauce commonly eaten with pasta, or smothering a fatty meal with ketchup. Nothing wrong with either option in moderation of course, but they're hardly healthy ways to get the lycopene you need every day.

So tomato juice in the purest form possible is probably the best means of obtaining significant dietary lycopene. That Bloody Mary with accompanying potato chips may be doing you some good after all!

Supplements containing lycopene are also readily available as an alternative, but opinions are divided as to their effectiveness. Conventional medicine tends to accept the value of a diet rich in carotenoids, but argues that the positive effects may be due to factors associated with such diets other than the carotenoids themselves. Alternative practitioners, of course, admit to no such doubts and are therefore convinced of the benefits of specific carotenoid supplementation.

So as ever, the commonsense advice for maximum benefit appears to be to combine supplementation with a normal daily diet already well supplied with lycopene rich foods.