Fact or Fiction: Raw veggies are healthier than cooked ones

Dovegetables lose their nutritional value when heated?

Cooking is crucial to our diets. It helps usdigest food without expending huge amounts of energy. It softens food, such ascellulose fiber and raw meat, that our small teeth, weak jaws and digestivesystems aren’t equipped to handle. And while we might hear from raw foodiststhat cooking kills vitamins and minerals in food (while also denaturing enzymesthat aid digestion), it turns out raw vegetables are not always healthier.

A study published in  last year foundthat a group of 198 subjects who followed a strict raw food diet had normallevels of vitamin A and relatively high levels of beta-carotene (an antioxidantfound in dark green and yellow fruits and vegetables), but low levels of theantioxidant lycopene.

Lycopene is a red pigment found predominantly intomatoes and other rosy fruits such as watermelon, pink guava, red bell pepperand papaya. Several studies conducted in recent years (at Harvard MedicalSchool, among others) have linked high intake of lycopene with a lower risk ofcancer and heart attacks. Rui Hai Liu, an associate professor of food scienceat Cornell University who has researched lycopene, says that it may be an evenmore potent antioxidant than vitamin C.

One 2002 study he did (published in the
Cooked carrots, spinach, mushrooms, asparagus,cabbage, peppers and many other vegetables also supply more antioxidants, suchas carotenoids and ferulic acid, to the body than they do when raw, Liu says.At least, that is, if they’re boiled or steamed. A January 2008 report in the
Deep fried foods are notorious sources of freeradicals, caused by oil being continuously oxidized when it is heated at hightemperatures. These radicals, which are highly reactive because they have atleast one unpaired electron, can injure cells in the body. The antioxidants inthe oil and the vegetables get used up during frying in stabilizing the cycleof oxidation.

Another study published in the  in 2002 showed that cooking carrots increases their level ofbeta-carotene. Beta-carotene belongs to a group of antioxidant substancescalled carotenoids, which give fruits and vegetables their red, yellow, andorange colorings. The body converts beta-carotene into vitamin A, which playsan important role in vision, reproduction, bone growth and regulating theimmune system.

The downside of cooking veggies, Liu says: itcan destroy the vitamin C in them. He found that vitamin C levels declined by10 percent in tomatoes cooked for two minutes—and 29 percent in tomatoes thatwere cooked for half an hour at 190.4 degrees F (88 degrees C). The reason isthat Vitamin C, which is highly unstable, is easily degraded through oxidation,exposure to heat (it can increase the rate at which vitamin C reacts withoxygen in the air) and through cooking in water (it dissolves in water).

Liu notes, however, that the trade-off may beworth it since vitamin C is prevalent in far more fruits and vegetables than islycopene. Among them: broccoli, oranges, cauliflower, kale and carrots.Besides, cooked vegetables retain some of their vitamin C content.

That said, research shows that some veggies,including broccoli, are healthier raw rather than cooked. According to a studyin the
Research published in the journal  in December 2008 found that sulforaphane might block theproliferation of and kill precancerous cells. A 2002 study in
On the other hand, indole, an organic compound,is formed when certain plants, particularly cruciferous vegetables such asbroccoli, cauliflower and cabbage, are cooked. According to research in  in 2001, indole helps kill precancerous cells before theyturn malignant. And while boiling carrots was found to increase carotenoidlevels, another study found that it leads to a total loss of polyphenols, agroup of chemicals found in raw carrots. Specific polyphenols have been shownto have antioxidant properties and to reduce the risk of cardiovascular diseaseand cancer, according to a 2005 report in
Comparing the healthfulness of raw and cookedfood is complicated, and there are still many mysteries surrounding how thedifferent molecules in plants interact with the human body. The bottom line,says Liu, is to eat your veggies and fruits no matter how they’re prepared.

"We cook them so they taste better,"Liu says. "If they taste better, we’re more likely to eat them." Andthat’s the whole idea.