Vegan Health ArticlesRaw versus Cooked Vegetables for Cancer Prevention
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From Michael Greger, MD

We know that vegetables in general prevent cancer, but a researcher at the Columbia University School of Public Health recently attempted to determine whether they are more protective raw or cooked.

Unfortunately, we have no studies directly comparing raw versus cooked veggies, so researchers had to review the totality of available research (published over the last decade) in an attempt to tease out the difference.

Cooking destroys some cancer-fighting nutrients, yet enhances the absorption of others. For example, by cooking your dark green leafy vegetables, studies show you may be destroying half of the antioxidant carotenoids.[1] At the same time, cooking may double carotenoid bioavailability, such that in the end your body might wind up with the same amount.[2]

Cooking vegetables increases the content of one type of fiber (soluble), which may help prevent cancer by decreasing insulin levels, but cooking decreases the content of another type (insoluble), which may help prevent cancer in a different way (by binding and excreting carcinogens).[3]

Cooking may reduce cancer risk by destroying some of the pesticides present in non-organic produce,[4] but cooking also destroys enzymes that may have beneficial effects. Wait, though, the American Dietetic Association just reviewed raw foods diets (October 2004) and concluded that one's stomach acid destroys the plant enzymes anyway so it doesn't matter if cooking destroys them first.[5] Yes, but digestion starts in the mouth, not in the stomach.

Raw garlic (in homemade salsa, guacamole, pesto, etc.) may be healthier than cooked because of an enzyme called alliinase, which produces a DNA-protecting compound called allicin when chewed in your mouth. One minute worth of microwaving, though, completely inactivates this enzyme, such that when you then chew it you absorb little or none of the protective allicin compound.[6]

The same thing happens in broccoli. There's an enzyme (called myrosinase) that produces special compounds whenever the plant's cell walls are ruptured (i.e. when you chew) that rev up your own liver's ability to detoxify carcinogens. But cooking inactivates the enzyme, such that people chomping down on steamed broccoli only seem to get about a third as much of these special cancer-fighting compounds.[7]

At the same time, cooking one's broccoli seems to increase the bioavailability of other cancer-fighters (called indoles) which help your body control hormone levels. Bottom-line, we should eat a combination of both cooked AND raw vegetables, which is exactly what the Columbia researcher found:

"It is clear from this review that both raw and cooked vegetables are inversely related to [in other words protective against] several... cancers. Although more of the studies showed a statistically significant inverse [protective] relationship between raw vegetables and cancer than either cooked or total vegetables, the literature is too varied to compare definitively... In the meanwhile the public should be encouraged to increase their vegetable intake and to consider eating some of them raw."[8]


1 Journal of the National Cancer Institute 82(1990):282.

2 Journal of Nutrition 128(1998):913.

3 Plant Foods in Human Nutrition 55(2000):207.

4 Journal of AOAC International 79(1996)::1447.

5 Journal of the American Dietetic Association 104(2004):1623.

6 Journal of Nutrition 131(2001):1054.

7 Nutrition and Cancer 38(2000):168.

8 Cancer Epidemiology, Biomarkers and Prevention 13(2004):1422.

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We began this archive as a means of assisting our visitors in answering many of their health and diet questions, and in encouraging them to take a pro-active part in their own health. We believe the articles and information contained herein are true, but are not presenting them as advice. We, personally, have found that a whole food vegan diet has helped our own health, and simply wish to share with others the things we have found. Each of us must make our own decisions, for it's our own body. If you have a health problem, see your own physician.