Whole grain diets could reduce the risk of bowel cancer

by Jennifer Bowden / 18 November, 2017
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There’s good news and bad about New Zealand’s second-biggest cancer killer. 

New Zealand has one of the highest rates of bowel cancer in the world, and diet clearly plays a role. So, could food trends be increasing our cancer risk?

Bowel cancer – also known as colon, rectal or colorectal cancer – is a malignant growth that develops in the intestine. It is the second-highest cause of cancer death in New Zealand. A family history of bowel cancer is a risk factor, and as we age, the chance of getting it increases.

Bowel cancer appears to be affecting more younger adults. A recent study based on 1995-2012 New Zealand National Cancer Registry data, published in the British Journal of Surgery, found the rate is climbing in people under 50. In contrast, there was a fall in the incidence in those aged 50-79.

New Zealand began rolling out a free national bowel-screening programme in July. However, its two-yearly checks are offered only to those aged 60-74.

The causes of the disease are unknown, but dietary and lifestyle factors have been linked to it. In September, the World Cancer Research Fund (WCRF) released a report analysing global research on the relationships between diet, nutrition, physical activity, weight and colorectal-cancer risk.

It concluded there was “convincing” evidence that processed meat, alcohol, being overweight or obese – and being tall – increased bowel-cancer risk. There was also a “probable” link to red-meat consumption.

On the positive side, the report said it is “probable” that whole grains, foods containing dietary fibre, dairy products and calcium supplements reduce the risk. This might give pause to paleo-diet followers, who avoid whole grains and, in many cases, dairy products. And also on the plus side is that physical activity reduces the risk.

It is the first time the WCRF has linked whole grains to reduced bowel-cancer risk. Its analysis suggests that eating three servings (about 90g) of whole grains a day cuts the risk by about a fifth. A serving is defined as half a cup of muesli or porridge, two wheat biscuits, a slice of wholegrain bread, or a cup of cooked brown rice or wholegrain pasta. So three servings could equate to two slices of wholegrain bread and half a cup of wholegrain muesli, for example.

There are a number of ways in which whole grains could be reducing bowel-cancer risk. For a start, whole grains are a source of dietary fibre, a fuel source for gut bacteria that in turn produce short-chain fatty acids, which have anti-inflammatory and anti-carcinogenic effects. Dietary fibre also reduces food’s transit time through the bowel, and may bind to carcinogens and prevent insulin resistance.

Whole grains are also a rich source of valuable biologically active compounds such as vitamin E, selenium, copper, zinc, lignans, phytoestrogens and phenolic compounds, many of which have “plausible anti-carcinogenic properties”, says the WCRF report.

Whole truth

Replacing refined grains with more wholesome ones is easy:

  • Eat wholegrain cereals for breakfast – try an oat-based porridge or whole-wheat cereal.
  • Swap white bread for whole-wheat or rye varieties.
  • Eat whole-wheat tortillas instead of white ones.
  • Replace white rice with brown or wild rice or bulgar.
  • Eat wholegrain pasta instead of standard pasta.
  • Add wild rice or barley to soups, stews, casseroles and salads.
  • In recipes, replace breadcrumbs with rolled oats or crushed whole-wheat bran.
  • Eat bran muffins rather than fruit muffins or scones.

This article was first published in the October 7, 2017 issue of the New Zealand Listener.

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