Many health organizations, including the World Health Organization and the National Cancer Institute, recommend five servings of fruit and vegetables daily to help ward off disease.
Some people (I’m not one of them) go even further and propose that eating enough fruits and vegetables provides strong protection from cancer.
Cancer is a complex group of diseases. We still know very little about what causes some cancers, but it’s probably safe to say that increased risk for most cancer types usually stems from a combination of factors—some genetic and environmental, which are hard to control, and some that we have much more power over. Smoking, exercise, obesity, diet and sun exposure have all been shown to affect cancer risk.
A healthy lifestyle has many components, and I personally don’t believe any one healthy diet habit by itself—even if practiced religiously over a lifetime—has a hugely dramatic effect on cancer incidence in a population.
Having said that, every little bit helps, and while we shouldn’t exaggerate any intervention as the “solution” to cancer, these small measures together do add up and help prevent some disease.
That, by the way, is why I see all health claims on food as at least a little misleading. The diet-health relationship is real, but is always more complicated and variable than what a simplistic statement implies.
A new study in the Journal of the National Cancer Institute got quite a lot of coverage in the past few days; it found what the authors called only a weak association between high fruit and vegetable intake and reduced overall cancer risk. The headlines in many news publications (“Eating Vegetables Doesn’t Stop Cancer " in the New York Times, “Fruit and vegetables have little effect on cancer risk, study finds ” in The Guardian) suggested deep disappointment over fruits and veggies’ “poor performance” against cancer.
Is this a blow to the five-servings-a-day advice? Let’s first take a closer look at the study.
Paolo Boffetta of the Mount Sinai School of Medicine in New York and colleagues analyzed data from the EPIC study (European Prospective Investigation into Cancer and Nutrition), which included almost 500,000 participants from ten Western European countries. In about nine years of follow-up, more than 30,000 participants were diagnosed with cancer.
The authors found a small but statistically significant association between high intake of fruits and vegetables and reduced overall cancer risk--the higher the intake the lower the risk.
The data shows a 3 percent lower risk of cancer for every 200 grams, or seven ounces, of fruits and vegetables a day a person eats. People who ate five or more servings a day had 11 percent fewer cancers than those who ate 0-1.5 servings a day.
These results were consistent across the countries studied.
Higher intakes of fruits and vegetables in this study group were associated with other healthy behaviors, such as smoking avoidance, limited alcohol consumption and exercise, which may also be protective from cancer. But the small protective effect of fruits and veggies persisted even after adjusting for these factors.
How significant is 3 percent protection from cancer?
Numbers are often hard to understand without context—they aren’t as absolute as they sound. Is 3 percent a small number?
There is of course no one right answer to that.
Let’s take a look at the Toyota recall and compare risk/benefit ratios.
The chance of an owner of a recalled Toyota experiencing a deadly acceleration problem is assessed at 2.8 in a million. (There were 17 fatal accidents related to acceleration in 10 years, before six million cars were recalled. New complaints are now pouring in, which is quite typical after a recall and law suits are announced.) But we all expect Toyota to recall and fix all relevant cars, and we’re angry they failed to address this problem sooner.
The yearly cancer incidence in the U.S. is estimated at 4,600 in a million; one and a half million Americans are diagnosed with cancer each year, and 1,500 die of cancer daily. If, as this study suggests, eating an additional seven ounces a day of fruits and veggies can reduce cancer incidence by 3 percent we’d have 40,000 fewer Americans receiving the diagnosis of invasive cancer yearly.
In Toyota's case we demand action when the current risk is as small as 2.8 in a million, yet with cancer, where the disease risk is as high as 4,600 in a million, some suggest that a reduction of 3 percent in risk does not make much of a difference.
I wouldn’t perhaps recommend a drug with many side effects if it reduced a rare disease’s risk by 3 percent, but for an “intervention” as benign as eating an additional apple a day, and a disease as serious and common as cancer a 3 percent risk reduction looks like a decent size reward.
What if fruits and veggies offer no protection from cancer?
When a study shows only a small difference in outcome between the studied groups, there’s also the possibility that this difference can be explained by chance, and by something other than the variable studied. In this case we have to bear in mind that eating more fruits and veggies is generally associated with a healthier lifestyle, and no matter how hard the authors try to control for the other healthy lifestyle factors, some bias may remain.
So even though this study and several others show a probable small reduction in all-cancer risk, let’s bear in mind that it’s also possible that eating your veggies might offer no significant protection from cancer.
Yet, this “worst case” scenario still leaves us with many excellent reasons to continue promoting fruits and veggies. Here’s a partial list of good reasons to eat plenty of fruits and vegetables:
• They help lower the risk of heart disease and stroke (a study showed a 30 percent lower risk in people eating five servings a day, compared to those who eat only 1.5 servings a day)
• They help lower blood pressure
• They help lower diabetes risk
• They help lower risk of eye (cataract and macular degeneration) and digestive (constipation and diverticulitis) problems
• They provide lots of fiber, both soluble fiber, which helps lower cholesterol and regulate sugar, and insoluble fiber, which is important to digestive health
• They provide vitamins, minerals and many other beneficial plant molecules—phytonutrients—many of which we’re only starting to understand. (And I’m sure there are a few we have yet to discover. My mom knew nothing about lycopene, for example, when she fed me tomatoes and watermelon.)
• They have high nutritional value and low caloric density, so eating many fruits and vegetables (rather than practically any other food) helps lower caloric intake and maintain optimal weight
• They taste good, are beautiful to look at, and connect us to nature
My last item on the virtues list is completely non-objective; I’m guilty of total fascination with colorful growing things that we can also eat.
If, in all the years that fruits and vegetables have been consumed and studied, the worst we can say about them is that they’re not as thick a shield against all cancers as some had hoped, this speaks to just how good for us they really are.
So keep those fruits and veggies coming!
Reposted as part of Food Renegate's Fight Back Fridays--go join the food fight!
This entry has been posted as part of The Kathleen Show's Prevention not Prescriptions