The full text of a review entitled “Fruit and vegetables and cancer risk” is available on the web site of the British Journal of Cancer, and it is not good news.
According to Professor Key, after many years of study there is minimal evidence that a diet high in fruit and vegetables will reduce risk for cancer in general (or for prostate cancer in particular). The article was also discussed on the Los Angeles Times Booster Shots blog yesterday.
In discussing the effect of diet on prostate cancer risk, specifically, Prof. Key writes as follows:
Risk [for prostate cancer] is increased in men with relatively high plasma concentrations of insulin-like growth factor-I, and levels of this growth factor can be affected by diet, but more research on this pathway is needed (Roddam et al., 2008). … recent large prospective studies suggest that there is little or no association between total fruit and vegetable intake and prostate cancer risk (Kirsh et al., 2007). There has been much interest in the possibility that fruits and vegetables, such as tomatoes, which are rich in the carotenoid lycopene might reduce the risk for prostate cancer, but overall the data do not support this hypothesis (Kavanaugh et al., 2007). Studies of soyabeans and prostate cancer have suggested that this vegetable may help to reduce risk, but the results are not conclusive (Hwang et al., 2009).
Having noted this, however, The “New” Prostate Cancer InfoLink believes that part of the problem in studying the impact of diet on all health risk has to do with time.
Most significant scientific study of the impact of diet on health risks dates back to little earlier than the late 1960s. This means that anyone of 50 or more today was born before any such significant research began, and that anyone over about 40 years of age, even if an organic food compulsive today, probably spent his or her childhood eating things that weren’t necessarily the best for their health.
Any really serious analysis of the impact of diet on risk for cancer (and other chronic health conditions) needs to be able to track diet back to infancy — and perhaps even maternal diet for (at least) the 9 months prior to birth. Why? Because we know that our development over time can be profoundly impacted by what we do when we are very young indeed, and there is at least a reasonable possibility that many of our risks for cancer are affected by things we do and eat in our formative years (e.g., growing up near to a chemical plant).
The bottom line is not that diet has no impact on cancer risk today. It is that we really don’t know whether diet has a significant impact on cancer risk. For the time being, however, as Prof. Keys concludes in his review:
Currently, advice in relation to diet and cancer should include the recommendation to consume adequate amounts of fruit and vegetables, but should put more emphasis on the well-established adverse effects of obesity and high alcohol intakes on cancer risk.
Of course when it comes to prostate cancer specifically, even the evidence of significantly increased risk as a consequence of high alcohol intake and obesity are less compelling that they are in some other cancers. But then again, these two particular problems are associated with much bigger risks than prostate cancer, and are a bad idea for a multitude of reasons — as is a poor diet.