Best Way to Cook All Those Vegetables

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May 20, 2008

WELL

Finding the Best Way to Cook All Those Vegetables

By TARA PARKER-POPE

By now, most people know they should be eating more vegetables. But

are there ways to get more from the vegetables you already eat?

A growing body of research shows that when it comes to vegetables,

it's not only how much we eat, but how we prepare them, that

influences the amount of phytochemicals, vitamins and other

nutrients that enter our body.

The benefits are significant. Numerous studies show that people who

consume lots of vegetables have lower rates of heart disease,

hypertension, diabetes, eye problems and even cancer. The latest

dietary guidelines call for 5 to 13 servings — that is two and a

half to six and a half cups a day. For a person who maintains her

weight on a 2,000-calorie-a-day diet, this translates into nine

servings, or four and a half cups a day, according to the Harvard

School of Public Health. But how should they be served?

Surprisingly, raw and plain vegetables are not always best. In The

British Journal of Nutrition next month, researchers will report a

study involving 198 Germans who strictly adhered to a raw food diet,

meaning that 95 percent of their total food intake came from raw

food. They had normal levels of vitamin A and relatively high levels

of beta carotene.

But they fell short when it came to lycopene, a carotenoid found in

tomatoes and other red-pigmented vegetables that is one of the most

potent antioxidants. Nearly 80 percent of them had plasma lycopene

levels below average.

" There is a misperception that raw foods are always going to be

better, " says Steven K. Clinton, a nutrition researcher and

professor of internal medicine in the medical oncology division at

Ohio State University. " For fruits and vegetables, a lot of times a

little bit of cooking and a little bit of processing actually can be

helpful. "

The amount and type of nutrients that eventually end up in the

vegetables are affected by a number of factors before they reach the

plate, including where and how they were grown, processed and stored

before being bought. Then, it's up to you. No single cooking or

preparation method is best. Water-soluble nutrients like vitamins C

and B and a group of nutrients called polyphenolics are often lost

in processing. For instance, studies show that after six months,

frozen cherries have lost as much as 50 percent of anthocyanins, the

healthful compounds found in the pigment of red and blue fruits and

vegetables. Fresh spinach loses 64 percent of its vitamin C after

cooking. Canned peas and carrots lose 85 percent to 95 percent of

their vitamin C, according to data compiled by the University of

California, Davis.

Fat-soluble compounds like vitamins A, D, E and K and the

antioxidant compounds called carotenoids are less likely to leach

out in water. Cooking also breaks down the thick cell walls of

plants, releasing the contents for the body to use. That is why

processed tomato products have higher lycopene content than fresh

tomatoes.

In January, a report in The Journal of Agriculture and Food

Chemistry concluded that over all, boiling was better for carrots,

zucchini and broccoli than steaming, frying or serving them raw.

Frying was by far the worst..

Still, there were tradeoffs. Boiling carrots, for instance,

significantly increased measurable carotenoid levels, but resulted

in the complete loss of polyphenols compared with raw carrots.

That report did not look at the effects of microwaving, but a March

2007 study in The Journal of Food Science looked at the effects of

boiling, steaming, microwaving and pressure cooking on the nutrients

in broccoli. Steaming and boiling caused a 22 percent to 34 percent

loss of vitamin C. Microwaved and pressure-cooked vegetables

retained 90 percent of their vitamin C.

What accompanies the vegetables can also be important. Studies at

Ohio State measured blood levels of subjects who ate servings of

salsa and salads. When the salsa or salad was served with fat-rich

avocados or full-fat salad dressing, the diners absorbed as much as

4 times more lycopene, 7 times more lutein and 18 times the beta

carotene than those who had their vegetables plain or with low-fat

dressing.

Fat can also improve the taste of vegetables, meaning that people

will eat more of them. This month, The American Journal of

Preventive Medicine reported on 1,500 teenagers interviewed in high

school and about four years later on their eating habits. In the

teenage years, many factors influenced the intake of fruits and

vegetables. By the time the study subjects were 20, the sole factor

that influenced fruit and vegetable consumption was taste. Young

adults were not eating vegetables simply because they didn't like

the taste.

" Putting on things that make it taste better — spices, a little

salt — can enhance your eating experience and make the food taste

better, so you're more likely to eat vegetables more often, " Dr.

Clinton said.

Because nutrient content and taste can vary so widely depending on

the cooking method and how a vegetable is prepared, the main lesson

is to eat a variety of vegetables prepared in a variety of ways.

As Susan B. Roberts, director of the energy metabolism laboratory at

the Tufts University Friedman School of Nutrition, put it, " Eating a

variety of veggies is especially important so you like them enough

to eat more. "

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