diet and cancer risks

An American study has just released, updating the latest findings regarding what we eat and our cancer risks. According to the media representation, this research means great news if you are short but cause for concern if you are overweight. It is the usual swings and roundabouts. The report itself is not a new or definitive study, rather it is a systematic review of recently published health studies.

Perhaps what fascinates me more about the report, released jointly by the World Cancer Research Fund and the American Institute for Cancer Research, is what sound bites the media runs with. The Age ran with Tall people 'at higher cancer risk’ over the weight issue (News Radio, ABC and the BBC). The Age also promoted the American Institute for Cancer Research study into people’s perception of cancer risks, making big news of there being no proven link between pesticides and cancer:

71 per cent thought that pesticide residue on produce was a cause - something that has never been shown; 56 per cent thought stress causes cancer, again not proven; and 49 per cent believed hormones in beef cause cancer.

However, is this what the report actually says and does the lack of evidence actually prove that these people’s perceptions are truly wrong? What the Diet and Cancer report actually found, concerning pesticide and herbicide risks, were much more complex than The Age implied.

There are theoretical grounds for concern, which are constantly reviewed by international and national regulatory bodies. However, there is no epidemiological evidence that current exposures are causes of cancers in humans, and so the Panel has made no judgements. Nevertheless, a precautionary approach is wise for women of reproductive age, since vulnerability during embryonic phases of development is increased, and early exposure may result in increased risk at later stages in life. (Diet and Cancer Report)

The panel did find studies that showed links between conventional food production and cancers but no specific epidemiological studies have been produced as yet. However they are concerned enough with the preliminary findings to suggest that “women of a reproductive age” (a significant chunk of the population) should take a “precautionary approach” to eating conventionally grown foods. Perhaps a more accurate headline should have screened “Don’t eat conventional food if you plan to get pregnant!" 71% of the 1000 Americans interviewed may not be so wrong after all.

The actual study document is dense and takes a lot of reading. I wonder if any of the journalists reporting on it poured over it? I always find inclusion criteria in such large scale analysis interesting. For example although we may think this all about humans and the food they eat, the panel included animal studies (genetically modified animals and rodent).

Overall the dietary recommendations made as a result of the report mimic much of what the naturopathic community has always said – pull way back on meat and dairy (yes, dairy a got specific mention) and focus more on plant foods such as whole grains, fruit and vegetables. Alcohol, salt, sweet drinks, processed meat and moulds (specifically afllatoxins, which are common to peanuts) got the thumbs down, while moving your body more received a predictable tick.

But the report is actually a lot more specific than this as there is no single "cancer", it exams the published literature on diet and specific cancers. The findings link eating carrots with cervical cancer protection, soy reducing prostate cancer and so on. However it was perplexing to find suggestions about cancer reduction linked to nutrients such as vitamins E, C and Selenium (the presumed link the panel was making regarding certain groups of foods) yet categorically implied people should not take nutritional supplements, which were not within the scope of the review.

Selenium is an interesting case in point. The cancer protective effects of this nutrient, would depend entirely on the soil it was grown in. New Zealand for example, has little or none, while in Australia anywhere near medicinal doses of selenium are considered a poison. So unless each individual study did an actual lab analysis of the foods these people were eating, they are making some leaps of faith in their conclusions.

The weight issue that was such a popular tag line in the press, is also slightly misrepresented. The Panel acknowledged being over weight (a BMI of 25-29) or obese (BMI >30) as a significant health risk. But will the lifestyle factors they surmised as being likely causes of weight gain, such as being sedentary, watching too much TV and consuming ‘energy dense’ (sugary or fatty) foods and drinks actually cause cancer? The conclusion was increased body fat “should be considered to be additional, indirect causes of (some) cancers”. (Chapter 8)

What about tall people, does height really determine cancer risk as the other popular headline suggests? The conclusion was not so obvious: “The Panel emphasizes that greater adult attained height, meaning how tall people are as adults, is unlikely directly to modify the risk of cancer”. Though there are odd implications that being tall may be a factor in some gynaecological and colorectal cancers, it was not suggesting that being short is necessarily a “get out of cancer free” card.

Keeping in mind that the study looks at the swings and roundabouts of individual cancers and that all cancers are not the same, the general conclusions about diet and cancer risk confirm nutritional and naturopathic commonsense:

Breastfeeding has benefits for both mother and child

Eat lots of vegetables, legumes and fruit

Ensure your diet has sufficient amounts of plant fibre, folate, vitamins B6, C, E, beta carotene (the vegetable form of vitamin A) and nutrients selenium, caratenoids, quercetin and lycopenes.

Eat less meat, this includes all meat of which processed meats get a special increased cancer risk mention

Cut out the cheese, though there are cancer factors for and against milk drinking

Don’t drink alcohol

There is a handy graph showing food risks and benefits at this summary.

Remember this study looked primarily at diet, rather than all lifestyle factors such as smoking and other recreational drugs).


So what’s for dinner tonight?