Moms frequently nag their kids with the line, “eat your fruits and veggies.” Many of us remember being served things like cabbage, tomatoes, yams, green beans, grapefruit and other so-called “healthy” foods before we could eat our ice cream and cookies! Well, it seems that our moms really did know best! Over the years, the medical literature has accumulated numerous studies that have supported the notion that a diet high in fruits and vegetables may modestly decrease the risk of certain diseases, including cancer. Indeed, many studies have shown that the Mediterranean diet is protective against several cancers. One of the main reasons this protection occurs is believed to be a direct result of frequent consumption of fruits and vegetables.
Some studies have shown that a diet rich in fruits and vegetables could reduce the risk of colorectal cancer by several percentage points. This protection is likely due to the content of phytonutrients contained in colorful fruits and vegetables. Numerous compounds such as polyphenols have been shown to decrease formation, growth, and spread of cancer cells by inhibiting complex growth pathways.
I recently came across an article published by Lee et al. in the World Journal of Gastroenterology (April 2017 issue) that I thought merited a quick blog. The researchers from South Korea performed a case-control study of 923 colorectal cancer patients and 1,846 control patients recruited from the National Cancer Center in Korea. Vegetables and fruits were categorized into four groups according to color: green, orange/yellow, red/purple, and white. Intake was classified by gender-specific tertiles (e.g., thirds) of the control group (those without colorectal cancer).
For the statistical nerds like me: The authors then used logistic regression to estimate odds ratios (OR) with 95% confidence intervals (CI). [Logistic regression is a complex statistical analysis that aims to assess an association with a studied variable(s) in population or case control studies. In this case, the resulting ORs tell us the relative percent reduction in risk of colorectal cancer from different levels of fruit and vegetable intake].
After adjusting for various confounding factors, the researchers found that higher total intake of vegetables and fruits was associated with a lower risk of colorectal cancer in women (OR=0.32, 95% CI 0.21-0.48, for those in the highest third of total intake compared to those in the lowest intake third). So, this means there was a 68% reduced risk in women with higher intake. The reduction in men was similar: OR=0.60, 95% CI 0.45-0.79; this translates into a 40% lower risk in men in the highest third of intake compared to those men in the lowest third.
This is an interesting study, though it does have its limitations by not being a randomized trial. However, I think it adds to the evidence that a higher intake of vegetables and fruits in general, may help decrease risk of colorectal cancer.
The idea that green fruits and vegetables decrease risk makes sense since they contain fiber, folate and phytonutrients such as sulphoraphane and indoles, which has been shown in previous studies to decrease cancer cell formation, growth and lead to cell death (apoptosis). Similarly, white fruits and vegetables (e.g., onions, leeks, garlic cauliflower, apples, pears, mushrooms,) decreased risk in both sexes, possibly by their vast array of phytonutrients.
In my opinion, it is safe to eat fruits and vegetables in any color group, as we should all strive for several servings of vegetables daily.
Mark A. Marinella, MD, FACP