By Walter C. Willett, M.D.
Choosing a plant-rich diet is one of the most
important—and enjoyable— ways to stay healthy.
The phrase “Eat your vegetables,
they’re good for you” springs out of the
parent’s mouth unbidden, like wisdom that must be
passed from generation to generation. That’s actually
pretty accurate. “Eat plenty of fruits and
vegetables” is timeless advice that science is only
now catching up to.
A diet rich in fruits and vegetables can decrease the
chances of having a heart attack or stroke; lower blood
pressure; help you avoid constipation; guard against two
common aging-related eye diseases?—? cataracts and
macular degeneration; help you feel full with fewer
calories; add variety to your diet and enliven your palate.
Potatoes Don’t Count
To a botanist, a fruit is any plant part that contains
seeds. In this article, I will stick with the culinary
concept of fruits as sweet dessertlike foods, and
vegetables as savory salad- or dinner-type foods. I am not
including potatoes in the vegetable category, even though
they are the most popular vegetable in America. Like rice
and pasta, potatoes are made up mostly of easily digested
starch. Studies show that eating potatoes isn’t
linked with the same health benefits as is eating other
vegetables and fruits.
Back in 1991, the National Cancer Institute launched its
5-a-Day public health campaign, urging us to eat five
servings of fruits and vegetables a day. This campaign has
been incorporated into the government’s Dietary
Guidelines for Americans. Five a day is a good start, but
it gives no real guidance on what qualifies. Two glasses of
orange juice, an apple, an order of french fries at lunch
and potatoes with dinner meets the 5-a-Day target. While
that’s better than no fruits and vegetables at all,
it doesn’t offer the full dose of health benefits
described here. Use five a day as a minimum, not a goal.
Don’t include potatoes in your daily tally, and try
to vary the fruits and vegetables in your diet.
While any one fruit or vegetable contains dozens, maybe
hundreds, of different compounds that your body uses for
something besides energy, no single fruit or vegetable
contains all the substances you need. It’s a good
idea to eat for color variety as well. Painting your diet
with the bold colors of ripe red tomatoes, crisp orange
carrots, creamy yellow squash, emerald-green spinach, juicy
blueberries, indigo plums, violet eggplants and all shades
in between not only makes meals more appealing, but also
ensures that you get a variety of beneficial nutrients.
Many Health Benefits
Prevent heart disease. A diet that includes plenty of
fruits and vegetables can help control or even prevent two
of the main precursors of heart disease and stroke: high
blood pressure and high cholesterol. Even better, investing
in a plant-rich diet pays off in terms of lowering your
chances of developing several forms of heart disease and
By combining the results of 17 large, long-term studies,
researchers estimated that people in the top tier of fruit
and vegetable consumption (about 35 servings a week or your
basic five a day) are 15 percent less likely to have a
heart attack or other problem caused by restricted blood
flow to the heart muscle than those in the bottom tier.
Among more than 100,000 men and women participating in the
Harvard School of Public Health’s Nurses’
Health Study and the Health Professionals Follow-up Study,
we found that eating about 30 servings of fruits and
vegetables a week (or just under five a day) was associated
with a 30-percent lower risk of the most common type of
stroke (ischemic stroke), the kind caused by a blood clot
blocking an artery in, or to, the brain. We calculated that
eating one extra serving of fruits or vegetables a day
decreases the chances of having an ischemic stroke by about
6 percent. In this study, most of the benefit seemed to
come from eating broccoli, spinach, kale, romaine lettuce,
and citrus fruit or juice.
Keep your eyes healthy. This goes way beyond the admonition
to eat carrots for better vision (actually better night
vision). A number of studies now show that people who
regularly eat dark-green leafy vegetables such as spinach
and collard greens are less likely to develop two common
aging-related eye diseases?—?cataracts and macular
degeneration. In both diseases, free radicals are believed
to be responsible for causing much of the damage. Free
radicals are highly reactive substances generated inside
the eye by bright sunlight, cigarette smoke, air pollution
and infection. Dark-green leafy vegetables contain two
pigments, lutein and zeaxanthin, that accumulate in the
eye. These two can snuff out free radicals before they can
harm the eye’s sensitive tissues
Avoid bowel trouble. Fiber sops up water like a sponge and
expands as it moves through the digestive system. By
triggering regular bowel movements, fiber can relieve or
prevent constipation. The bulking and softening actions of
fiber also decrease pressure inside the intestinal tract
and so may help prevent diverticulosis (the development of
tiny, easily irritated pouches inside the colon) and
diverticulitis (the often painful inflammation of these
Twenty-five years ago, two eminent epidemiologists
estimated that “dietary factors” accounted for
35 percent of cancer deaths in the United States, or
roughly the same amount as were chalked up to smoking at
the time. While 35 percent may be overly optimistic, the
basic message that better diets?—?heavy on the plant
foods, please?—?help guard against a variety of
cancers is perfectly sound.
So far, more than 200 studies have looked at the connection
between diets high (or low) in fruits and vegetables and
the development of cancer. Initially, they estimated a
50-percent reduction in most major cancers if everyone got
at least five servings of fruits and vegetables a day. That
was the basis of the National Cancer Institute’s
ongoing 5-a-Day program.
Most of the early studies were case- control studies. In a
nutshell, these involve comparing differences in diet,
habits and other possible causes of cancer between a group
of people with a particular cancer and a group without it.
Such comparisons aren’t always fair or without bias.
People with cancer, for example, tend to seek reasons for
why they were stricken and may be more apt to find fault
with their diets than those without the disease. The
consistency of results from case-controlled studies created
a deceptively strong idea that eating plenty of fruits and
vegetables helped ward off cancer.
Cohort studies, in which information on diet and other
lifestyle factors are collected before cancer, heart
disease and other conditions occur, tend to give more
reliable and durable results. Not long ago, our team at the
Harvard School of Public Health combined information on
fruit and vegetable consumption and cancer from our two
large cohort studies after the 110,000 participants had
been followed for almost 20 years. During this time, 9,100
had developed some type of cancer. Those who averaged eight
or more servings of fruits and vegetables a day developed
cancer at about the same rate as those who ate fewer than
one-and-a-half servings a day.
Does this mean that eating fruits and vegetables has no
impact whatsoever on cancer risk? No. Although they
don’t have a blanket anti-cancer effect, fruits and
vegetables may work against specific cancers. The
International Agency for Research on Cancer commissioned an
exhaustive review of the hundreds of case-control and
cohort studies that have looked at fruit and vegetable
consumption and cancer over the years. Drill down a bit
into the data and there’s some evidence that certain
types of fruits or vegetables work against specific
cancers. Examples include the following:
• Eating cruciferous vegetables such as broccoli has
been linked to lower rates of bladder cancer.
• There is strong evidence that the vitamin folic acid
helps protect against colon and rectal cancer. Vegetables
such as spinach and beets are good sources of folic acid.
• Lycopene from tomatoes and cooked or processed
tomato products such as tomato sauces or ketchup seems to
be helpful in the prevention of prostate cancer.
Putting it into Practice
There isn’t any magic daily number or combination of
fruits and vegetables for optimal health. Instead, I offer
two words of advice: more and different.
Aim high. Use five servings a day as a minimum goal and
shoot for more.
Eat for variety and for color. On most days, try to get at
least one serving from each of the following fruit and
• dark-green, leafy vegetables.
• yellow or orange fruits and vegetables.
• red fruits and vegetables.
• legumes (beans) and peas.
• citrus fruits.
Cook your tomatoes. Treat yourself to tomatoes, processed
tomatoes or tomato products cooked in oil on most days.
Tomatoes are rich in lycopene, a powerful antioxidant that
has been linked with lower rates of a variety of cancers.
Because lycopene is tightly bound inside cell walls, your
body has a hard time extracting it from raw tomatoes.
Cooking breaks down cell walls, and oil dissolves lycopene
and helps shuttle it into the bloodstream.
Fresh is better. Eat several servings of fresh, uncooked
fruits and vegetables each week because cooking damages or
destroys some important nutrients. Vitamin C and folic
acid, for example, are sensitive to heat. Truly fresh
fruits and vegetables add enormously to the pleasure of
eating a healthy diet. The freshest produce is what you
grow yourself and pick just before you eat it.?
Walter C. Willett, M.D., is chair of the Department of
Nutrition at the Harvard School of Public Health and a
professor of medicine at the Harvard Medical School.