Finding the Best Way to Cook
All Those Vegetables
Published: May 20, 2008
By now, most people know they should be eating more vegetables.
But are there ways to get more from the vegetables you already eat?
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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,
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
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
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.”