Fruit and vegetables and cancer risk

Another one to clear off my open tabs… a nice little review of dietary factors influencing cancer…

Fruit and vegetables and cancer risk (pdf)

The possibility that fruit and vegetables may help to reduce the risk of cancer has been studied for over 30 years, but no protective effects have been firmly established. For cancers of the upper gastrointestinal tract, epidemiological studies have generally observed that people with a relatively high intake of fruit and vegetables have a moderately reduced risk, but these observations must be interpreted cautiously because of potential confounding by smoking and alcohol.

For lung cancer, recent large prospective analyses with detailed adjustment for smoking have not shown a convincing association between fruit and vegetable intake and reduced risk.

For other common cancers, including colorectal, breast and prostate cancer, epidemiological studies suggest little or no association between total fruit and vegetable consumption and risk.

It is still possible that there are benefits to be identified: there could be benefits in populations with low average intakes of fruit and vegetables, such that those eating moderate amounts have a lower cancer risk than those eating very low amounts, and there could also be effects of particular nutrients in certain fruits and vegetables, as fruit and vegetables have very varied composition.

Nutritional principles indicate that healthy diets should include at least moderate amounts of fruit and vegetables, but the available data suggest that general increases in fruit and vegetable intake would not have much effect on cancer rates, at least in well-nourished populations. Current advice in relation to diet and cancer should include the recommendation to consume adequate amounts of fruit and vegetables, but should put most emphasis on the well-established adverse effects of obesity and high alcohol intakes.

I read through the paper looking for any reference that meat and/or fat intake might be a dietary factor implicated in the development of cancer – as again, conventional wisdom suggests that this is the case, particularly with regard to cancers of the gastrointestinal tract.  The only mention was with regard to colorectal cancer;

The incidence of this cancer is generally high in populations with high intakes of meat and low intakes of staple plant foods (Armstrong and Doll, 1975), and it has long been suggested that dietary fibre might reduce risk (Burkitt, 1971).

However, the authors note the outcome of the Women’s Health Initiative with regard to this;

In the Women’s Health Initiative randomised trial, the intervention was a low-fat eating pattern aimed at reducing dietary fat intake and increasing consumption of vegetables, fruits and grains; there was an average increase in fruit and vegetable intake of 1.1 servings per day, and the dietary intervention did not cause any significant change in the incidence of colorectal cancer after 8 years (Beresford et al, 2006). Overall, the data do not show a clear association between fruit and vegetables and the risk for colorectal cancer, although they are compatible with a small reduction in risk.

The Science Daily write up provided a good summary;

There is no convincing evidence that eating more fruit and vegetables can reduce chances of developing cancer, although they are important for maintaining a healthy diet.

That’s the conclusion of a review by an Oxford University scientist that looked at a decade of evidence on the links between fruit and vegetables and the development of cancer.

The study, published in the British Journal of Cancer, found that the only diet-related factors that definitely affect cancer risk are obesity and alcohol. Tobacco is still the single biggest cause of cancer.

Professor Tim Key of the Cancer Epidemiology Unit at Oxford University says that while there are undoubted benefits in eating fruit and vegetables, there is little hard evidence that they protect against cancer. But the evidence is indisputable that cancer is strongly linked to being overweight or obese and drinking more alcohol than the recommended daily limits.

He said: ‘Fruit and vegetables are an important part of a healthy diet and a good source of nutrients. But so far the data does not prove that eating increased amounts of fruit and vegetables offers much protection against cancer.

‘But there’s strong scientific evidence to show that, after smoking, being overweight and alcohol are two of the biggest cancer risks.’

Overweight people produce higher levels of certain hormones than people of a healthy weight and this can contribute to an increased risk of breast cancer.

Being overweight can increase your risk of other common cancers like bowel, and also hard-to-treat forms of the disease like pancreatic, oesophageal and kidney cancer.

When alcohol is broken down by the body it produces a chemical which can damage cells increasing the risk of mouth, throat, breast, bowel and liver cancers.

Sara Hiom, director of health information at Cancer Research UK, said: ‘Too few people know about the significant cancer risks associated with obesity and drinking too much alcohol. While stopping smoking remains the best way to cut your chances of developing cancer, the importance of keeping a healthy weight and cutting down on alcohol shouldn’t be overlooked.

‘Keeping alcohol intake to a maximum of one small drink a day for women and two small drinks per day for men and keeping weight within the healthy limits can have an enormous impact.’

No prizes for guessing what dietary pattern is driving the hormonal changes associated with obesity – grains, fructose, industrial seed oils.  So in this regard, there are dietary factors associated with cancer… the same dietary factors driving inflammation in the body.  Which leads nicely to a post on why aspirin has been shown to help reduce cancer rates… but why diet and lifestyle is still going to be better.

2 thoughts on “Fruit and vegetables and cancer risk

  1. Primal Fed

    I suppose it would be hard to accurately study, but I wonder if there is a difference in the rates of those eating conventional farmed fruits and vegetables vs. wild or organic.

  2. O Primitivo

    In order to avoid cancer, it's useless to eat more fruit and vegetables alone if, at the same time, the inflammatory, hyperinsulinemic and immune supressing factors are ignored. And these are all related to modern lifestyle, not only to food. In the WCRF/AICR-2007, page 116 ( you can read "Findings from cohort studies conducted since the mid-1990s have made the overall evidence that vegetables, or fruits, protect against cancers, somewhat less impressive. In no case now is evidence of protection judged to be convincing". Tobacco/urban pollution are inflamamatory/bad (low-grade chronic inflammation), but nobody knows exactly what causes cancer, so official messages are contradictory. There is an important editorial on this issue here: Aspirin effect on cancer risk reduction is awfull, look at the typical NNT numbers, worst that statins for CVD.

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