Raw versus Cooked Vegetables for Cancer Prevention
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
At the same time, cooking may double
carotenoid bioavailability, such that in the end your body might wind
up with the same amount.
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).
Cooking may reduce cancer risk by destroying some of the pesticides
present in non-organic produce, 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.
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.
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.
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...
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."
13 Journal of the National Cancer Institute 82(1990):282.
14 Journal of Nutrition 128(1998):913.
15 Plant Foods in Human Nutrition 55(2000):207.
16 Journal of AOAC International 79(1996)::1447.
17 Journal of the American Dietetic Association 104(2004):1623.
18 Journal of Nutrition 131(2001):1054.
19 Nutrition and Cancer 38(2000):168.
20 Cancer Epidemiology, Biomarkers and Prevention 13(2004):1422.
Source: November/December 2004 issue of Dr. Michael Greger's "Monthly" Newsletter
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