HOW TO PREVENT CANCERS

The headlines this week about fruits and vegetables doing little, if anything, to lower cancer risk may entice you to reach for a candy bar rather than a carrot (study), but there's still plenty of good reasons to keep working on your 5 or more each day.

Most importantly, there's still very good evidence that eating a diet rich in fruits and vegetables can significantly lower the risk of heart disease and stroke - two major killers in the United States.  One 2004 study that included over 70,000 participants from the Nurses' Health Study and over 35,000 participants from Health Professionals Follow-Up Study found that those people eating eight or more servings of fruits and vegetables per day had a 30 percent lower risk of cardiovascular disease than those eating less than 1.5 servings per day (study) (1).  On top of this, studies also strongly suggest that a diet high in plant foods can lower the risk of diabetes and high blood pressure (2,3), and help keep weight in check (4,5).

In terms of cancer risk, while it's true that the recent study out of Europe that included over 400,000 people followed over eight years found only a very small benefit from eating fruits and vegetables, it's important to keep some things in mind when looking at these results (6).

First, they don't rule out a benefit for specific cancers from eating specific fruits and vegetables.  It can get fairly complicated, fairly quickly, but the European study looked at links between overall cancer risk and overall fruit and vegetable intake.  Yet, there is good evidence that some certain types of fruits and vegetables may lower the risk of some certain types of cancer.  For example, diets high in tomato-based foods have been found in previous studies to lower the risk of prostate cancer and diets rich in yellow/orange vegetables have been found to lower the risk of lung cancer (7-9).  The broad approach of the European study could have washed out such targeted benefits.

Second, the study only looked at adult intake of fruit and vegetables.  One thing that's become clear over the years is that when a person is exposed to a factor can have important implications on how it affects cancer risk. The time frame for prevention matters.  Radiation is one good example, and one mentioned in the editorial accompanying the study (editorial) (10).  The younger a person is when exposed to a given amount of radiation, the greater the impact that exposure will have on later cancer risk.  Soy intake and breast cancer risk is another prime example, with studies showing that the reduced risk linked to high soy intake may be strongest for intake in childhood and adolescence (11). The relationship could be similar with fruits and vegetables.  Eating a diet rich in fruits and vegetables early in life could have a much bigger impact on lowering cancer risk than such a diet later in life.  Looking at diet so late and only a few years before cancer is diagnosed may be looking in the wrong place. (See related post).

The results of this new study are little surprise to the scientific community, who have seen the cancer benefits of total fruit and vegetable consumption dwindle as good evidence has accumulated over the past ten years.  Yet, the overall health benefits of a diet rich in fruits and vegetables aren't in question when you look beyond cancer to heart disease, stroke, diabetes, and weight control.