What I have seen about tomatoes is that after some cooking the amount of lycopenes is either increased - or mor easily absobred - but that doesn't actually mean that cooked tomatoes are healthier cooked than raw. It only says something about one single component in tomatoes - and nothing about the levels of minerals, vitamins, antioxidants/phytosterols/flavonoid compounds - or the other carotenoids (beta-carotene, gamma-carotene, phytone etc) in cooked vs raw tomatoes.
This tomatoe/lycopenes example's I've heard (again and again) for cooking plants. Beta-carotene levels in carrots have also been mentioned + phenolic antioxidants in some plants. (More info in the links below).
Some people seem to use these two examples as an 'alibi' for eating cooked food (as if they need one!), by not mentioning all the other plants and nutrients out there. Several other vitamins are reduced ny cooking at high temperatures, there are other sources of lycopene (grapefruit, watermelon and many others), and raw tomatoes also have high levels of lycopenes. But why not just eat both cooked and raw tomatoes?
The studies about lycopene boost in tomatoes are conflicting, by the way. If I remember right, one mention a ten times boost, while another only found a 35% increase.
Tomatoes are mainly made out of water (almost 95% by weight), so anything which removes some of that water would increase the ratio of the nutritional 'goodies' in that plant if the same goodies aren't killed in the process. Some will insist that sundrying is better than cooking, and when it comes to cooking, steaming may be better in some cases, but worse (than boiling) in others.
It is now maybe 15-20 years ago it was found that men who consumed tomato products had fewer cases of prostate cancer, which started the discussion about lycopenes in tomatoes. But since them, the link between eating plants - raw or cooked - has been confirmed by a lot of other findings as well, so maybe the whole thing about lycopenes is a bit exaggerated.
Some links:
Raw vs. Cooked Veggies: A Nutrition Smackdown
Is raw or cooked food better?
Top 10 foods highest in lycopene (9 of them are plants)
Food sources for lycopene
From the last link above:
Quote:
The Arguments Against Lycopine
Although there is question that fruits and vegetables high in lycopene had shownprotective and curative effects against prostate cancer and other cancers, many scientistsare not convinced that lycopene is the one which is doing the trick.
Some argue that it is the antioxidant properties of lycopene that is really beneficialcombined with complex interaction with other micronutrients present in the food. Thereare other examples of herbs or foods that provides the beneficial effect. Then comes thescientists and propose an active ingredient responsible for this benefit. On further study,we find that the proposed active ingredient, given alone, cannot reproduce the healingresults identified with the whole food or whole herb. I am a strong proponent of takingthe whole food or herb as opposed to supplements.
Don't rely on lycopene supplements. Eat tomatoes and tomato-containing foods as part ofa diet rich in fruits and vegetables. We know they work. Go for it.
Recommendations:
Take 1 to 2 servings of lycopene-rich tomato or tomato products every day for maximumprotection against cancers. Cooked tomato products (especially cooked in olive oil) is themost beneficial. Lycopene is not well absorbed unless it has been heated. Tomato sauce,tomato paste, and catsup are the best sources. Avoid foods that are high in sugar and salt.
Buy the reddest tomatoes you can find. They contain the most lycopenes.