Fruits & veggies have limited effect on cancer says new stud

[runrevolt]

http://blogs.indystar.com/fitforlife/20 ... _vegg.html

[Fallen_Horse]

Nice try, but I wonder how many of those studies counted ketchup (catsup) as a veggie and sugared orange juice as a fruit....

[iain_g]

The main finding, writes the Harvard Medical School's Health Publications, was that each 7-ounce portion of fruit and vegetables consumed (two servings' worth) lowered cancer risk by only 4 percent. That's much less than previous estimates of fruits and vegetables reducing cancer risk by 50 percent.

The article misses out one detail that is just slightly important: the 7-ounce portion mentioned should be PER DAY (and btw 7 ounces is about 200 grams). Otherwise it would suggest that eating 5kg of fruit & veg over a 9-year period would result in a cancer risk of zero......

[vegimator]

Jack Norris had an interesting post on this study:

The study showed that adding 200 g of fruits and vegetables per day decreased the risk of cancer by 4%. What the reports didn’t mention was that people who ate more than 647 grams of fruit and vegetables per day (the equivalent of about 2 cups of broccoli plus 2 1/4 medium apples) had an 11% reduced risk of cancer compared to those who at only 226 g per day (the equivalent of about 3/4 apple plus 3/4 cup of broccoli).

http://jacknorrisrd.com/?p=1028

[iain_g]

That's an interesting link, thanks. The author is being _slightly_ naughty by comparing the extreme values within the quintiles i.e. the maximum consumption of people within the first quintile and the minimum within the 5th quintile. It would be better to use some kind of 'typical' or average daily consumption value within the quintiles. In the 1st quintile this might be expected to be close to 113g per day and in the 5th quintile, well we have no idea without further information. It would be a good bit higher than 647 gram/day at any rate. Let's just say it's 747 g/day. The difference between these two average consumption values for the top and bottom quintiles is then somewhat over 600g, from which we would expect a risk reduction of a bit over 12%, going by the headline 4% claim. This is in fact a bit stronger than the 11% mentioned.

[Gelert]

Nice try, but I wonder how many of those studies counted ketchup

May as well, given the increased lycopene bioavailability in it. Better than unprocessed tomatos in that respect.

Original article here.

http://jnci.oxfordjournals.org/cgi/reprint/102/8/529

Background: It is widely believed that cancer can be prevented by high intake of fruits and vegetables. However, inconsistent results from many studies have not been able to conclusively establish an inverse association between fruit and vegetable intake and overall cancer risk.

Methods: We conducted a prospective analysis of the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort to assess relationships between intake of total fruits, total vegetables, and total fruits and vegetables combined and cancer risk during 1992–2000. Detailed information on the dietary habit and lifestyle variables of the cohort was obtained. Cancer incidence and mortality data were ascertained, and hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox regression models. Analyses were also conducted for cancers associated with tobacco and alcohol after stratification for tobacco smoking and alcohol drinking.

Results: Of the initial 142 605 men and 335 873 women included in the study, 9604 men and 21 000 women were identified with cancer after a median follow-up of 8.7 years. The crude cancer incidence rates were 7.9 per 1000 person-years in men and 7.1 per 1000 person-years in women. Associations between reduced cancer risk and increased intake of total fruits and vegetables combined and total vegetables for the entire cohort were similar (200 g/d increased intake of fruits and vegetables combined, HR = 0.97, 95% CI = 0.96 to 0.99; 100 g/d increased intake of total vegetables, HR = 0.98, 95% CI = 0.97 to 0.99); intake of fruits showed a weaker inverse association (100 g/d increased intake of total fruits, HR = 0.99, 95% CI = 0.98 to 1.00). The reduced risk of cancer associated with high vegetable intake was restricted to women (HR = 0.98, 95% CI = 0.97 to 0.99). Stratification by alcohol intake suggested a stronger reduction in risk in heavy drinkers and was confined to cancers caused by smoking and alcohol.

Conclusions: A very small inverse association between intake of total fruits and vegetables and cancer risk was observed in this study. Given the small magnitude of the observed associations, caution should be applied in their interpretation.

Always worth examining the original article rather than its diminishing returns in the blogosphere.

My two cents is that the approach advocated by Norris: X amount of F&V reduces cancer by Y, ergo 5X will reduce cancer by 5Y - a broadly linear dose response that is, has some hypothetical merit perhaps. But is it going to work in the real world? How successful have 5-a-day campaigns been to date - not much. (Just the other day I was in a GP's surgery which had a poster up on the nutritional benefit of F&V which cited peas as a good source of vitamin B12 ffs!) Is saying 10 a day going to help? Particularly against the backdrop of the previous message on 5-a-day being invalidated!

I remain a little sceptical. Even if the approach taken by Norris is adopted, we're still seeing a HR of 0.90 compared to the 0.97 values seen.

As I've said before (ad nauseum) in the debate about diet and cancer, it isn't unimportant but there are other initiatives which are far more important IMO.

For a quick and contemporary example, shoving a camera probe up people's arses once in their lifetime to look for signs of colorectal cancer.

A recent multicentre RCT study (Atkin et al. 2010 Lancet 375:1624-1633) shows that this has major impacts. It cut actual incidence by 23% (HR=0.77) and death by 31% (HR=0.69). After adjustment for self-selection the impacts increased to cuts of 33% and 43% respectively. It halved the rate of death from one kind of colorectal cancer and the authors concluded that for every 191 bums abused by fibre optics, a life was saved.


But that doesn't get clicks on nutrition websites...