Colorectal cancer is cancer that develops in the large intestine. Some intestinal conditions are associated with the development of colorectal cancer but for most, the causes are unknown. Nutrition has been a point of interest for research into risk factors for colorectal cancer. Unfortunately, studies on the impact of diet on colorectal cancer risk have had inconsistent results or very small effects. Diets high in fruits and vegetables are generally considered to reduce the risk of many cancers but research has yet to find consistent benefits against colorectal cancer.
Researchers from London conducted a review of previous trials that had examined the benefits of fruits and vegetables for colorectal cancer prevention. The review, published in Gastroenterology, found that there was a small decrease in colorectal cancer in participants with the highest levels of fruit and vegetable consumption.
The meta-analysis included 19 prospective cohort studies. Each study evaluated the effect of fruits and vegetables on the risk of colorectal cancer. Overall, the incidence of colorectal cancer was less than 1% of all participants. The participants were divided according to the amounts of fruits and vegetables they reported in their diet. A lower risk of colorectal cancer was noted in participants with:
- The highest fruits and vegetable intake compared to the lowest intake group — in an analysis of 11 studies with 1,523,860 participants
- The highest fruit intake compared to the lowest intake group — in an analysis of 14 studies with 1,558,147 participants
- The highest vegetable intake compared to the lowest intake group — in an analysis of 16 studies with 1,694,236 participants
A meta-analysis can increase the reliability of study outcomes by creating a large pool of participants from similar studies. This analysis had a very large pool of participants, which should increase its reliability. However, the meta-analysis is only as reliable as the studies that are included. In this case, the included studies are all observational studies, which are a less reliable study design. In addition, there were a very small percentage of participants that developed colorectal cancer. These factors may mean the effects of fruits and vegetables on colorectal cancer may be overexaggerated or under-represented.
A diet high in fruits and vegetables has been associated with a decreased risk of cancer in general. They are also associated with a range of other health benefits, so it can't hurt to bulk up your fruits and veggies. Some organizations recommend at least five servings per day but this may be higher based on how many overall calories you need. An easy way to begin is to make fruit or vegetable readily available for snacks through the day and having one to two servings of fruit or vegetables at each meal. The Centers for Disease Control and Prevention (CDC) also has a website (listed below) to help you determine how many fruits and veggies you should eat.
Aune D, Lau R, Chaun D, et al. Nonlinear reduction in risk for colorectal cancer by fruit and vegetable intake based on meta-analysis of prospective studies.
Gastroenterology. 2011 Jul;141(1):106-18. Epub 2011 Apr 16.
by Brian P. Randall, MD
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