A large European study finds fruits and vegetables are only
modestly protective against cancer, but it's a different story
for heart disease.
We've gotten used to flip-flops in health advice by now, but the
recommendation to eat plenty of fruits and vegetables looked to
be incontrovertible. Science seemed to support the folk wisdom
about what an apple per day would keep away. Actually, make that
five apples (or oranges or peaches or servings of arugula),
because in 1990 the World Health Organization (WHO) recommended
that people eat five daily servings of fruits and vegetables
(about 14 ounces worth) to prevent cancer and other chronic
diseases. A year later, the National Cancer Institute came up
with its 5-a-Day program to promote fruit and vegetable
consumption. For years, cancer prevention had revolved around
telling people what not to do — smoke cigarettes. Now
the experts and public health officials had an opportunity to
tell us what we should do — load up on the fruits and
But since those salad days, study findings have been chipping
away at the notion that fruit and vegetable consumption protects
against cancer. It didn't get much attention at the time, but
Harvard researchers reported results in The Journal of the
American Medical Association in 2001 that suggested fruit
and vegetable consumption in adulthood really didn't have any
effect on the risk of getting breast cancer. Two years later, the
International Agency for Research on Cancer, a branch of the WHO,
said the evidence for overall cancer protection was limited.
Experts knew that a shift was under way, but the public didn't,
so study results reported in The Journal of the National
Cancer Institute in April 2010 took many people by surprise.
The headlines accurately reflected the study's main conclusion:
fruit and vegetable intake has a very small effect on cancer
risk. In an accompanying editorial, Dr. Walter C. Willett, chair
of the nutrition department at the Harvard School of Public
Health and a member of the Health Letter's editorial
board, said that "any association of intake of fruits and
vegetables with the risk of cancer is weak at best."
It wasn't a complete reversal; after all, "weak at best" is
better than nothing. (Thanks goodness we didn't find ourselves
trying to figure out how fruits and vegetables might cause
cancer!) But there are some lessons to be learned from how what
seemed a sure thing now seems less so. And for reasons we'll
explain, giving up on fruits and vegetables is not one of them.
The results reported in April 2010 were from the European
Prospective Investigation into Cancer and Nutrition study, also
known as the EPIC study. Ordinarily, the results from a single
study wouldn't be given much weight, but in health research,
there's credibility in numbers, and the size of the EPIC study
matches its acronym. By cobbling together the cohorts of various
studies, the EPIC researchers have assembled a juggernaut of a
study that includes data on almost half a million people from 10
The fruit and vegetable investigation was fairly straightforward.
The researchers pulled together data on fruit and vegetable
intake from answers to dietary questionnaires. Cancer registries
showed that about 30,000 people in the EPIC cohorts had gotten
cancer over the follow-up period of about nine years. And some
sophisticated, but standard, statistical techniques were used to
calculate how fruit and vegetable consumption might be related to
the likelihood of being among those who got cancer. The EPIC
researchers had conducted similar studies for particular types of
cancers, but this time they lumped the cancers together, which
increased the statistical certainty.
The main finding was that each 7-ounce increment in fruit and
vegetable consumption — or about two servings' worth — lowered
cancer risk by a modest 4%. That may seem okay, especially if you
were to eat five servings a day. But it pales in comparison to
earlier estimates of a 50% risk reduction from fruits and
Some further analysis by the EPIC researchers showed that
vegetables may have more of an effect on cancer risk than fruits,
and that fruits and vegetables together may have more of an
effect among people who drink lots of alcohol. The possible
benefit for heavy drinkers fits with evidence from other research
that alcohol creates some vulnerability to cancerous processes
that may be countered by folate, a B vitamin found in many fruits
Four morals to the story
There are any number of morals to the story of how cancer
protection from fruit and vegetables came down to earth. Here are
four of them:
1. Case-control studies may mislead. As
Dr. Willett explained in his editorial, much of the evidence for
a large protective effect from fruits and vegetables came from
case-control studies, and case-control studies tend to amplify
the effect of risk factors for a couple of reasons. For one
thing, they rely on memories of past behaviors and events, and
people are prone to recall bias: selective memory for whatever
they believe caused their condition (if they're cases) or
prevented it (if they're the healthy controls).
Another problem is that the healthy controls in such studies tend
to be people who are exceptionally health-conscious. That means a
habit like high fruit and vegetable intake may seem more
responsible for good health than it actually is.
2. Likable ideas win popularity
contests. In health, as in other matters, we're
more likely to accept ideas and follow advice that's appealing
and leaves our other notions intact. Fruit and vegetables have a
wholesome image. Studies showed — and experts believed — that
antioxidants and fiber had important anticancer properties. So
why wouldn't the foods that contain them also? It was only later
that estimations of fiber and antioxidants as cancer fighters
3. Something that comes "out of the blue" usually
hasn't. The EPIC study results seemed to come out
of nowhere to upend views about diet and cancer prevention. But,
as mentioned earlier, it was just the latest in a number of
findings that have called into question the size of a protective
effect from fruits and vegetables.
4. Every study leaves stones unturned.
One way to limit the frustration with the back-and-forth in
health news is to recognize that health research is almost always
a work in progress. No study answers all the questions.
Consider the EPIC study results and all the questions it raises.
Is nine years a long enough follow-up period for a cancer study?
How applicable are results for Europeans to the rest of humanity?
Could "exposure" to fruit and vegetables in adulthood be too
late? Perhaps consumption in childhood and the teen years matters
Don't give up on them
Even if the EPIC study results hold up, and fruits and vegetables
prove to be minor players in cancer prevention, we shouldn't give
up on them.
Cancer isn't the only foe, and there's good evidence from
reliable studies (not just case-control comparisons) that eating
fruits and vegetables lowers the risk of having a heart attack,
stroke, and some other forms of cardiovascular disease. A large
Harvard study found a 30% difference in cardiovascular risk
between high and low fruit and vegetable intake.
Nor is it time to give up cancer prevention. We can choose not to
smoke — and quit if we do. We can work to stay slim: being
overweight is associated with a higher risk for many cancers. In
fact, by some measures, extra heaviness now accounts for about
the same number of cancers as active smoking. And we can
exercise. Physical activity is associated with lower risk of
several important cancers.