New World Cancer Research Fund Report supports dietary fibre for protection against colorectal cancer
The number of new cancer cases in Australia is rising each year. Data from 2007 (AIHW) indicates that bowel cancer (also known as colorectal cancer) is the second most common cancer in Australia and the second largest cause of cancer deaths in Australia, killing almost 80 people a week (Bowel Cancer Australia).
Rates of colorectal cancer increase with industrialisation and urbanisation and are generally more prevalent in high income countries, but now becoming increasingly more common in middle and low income countries. Somewhat more common in men than in women, colorectal cancer is fatal in just under half of all cases, however if detected early, it is actually one of the most curable cancers, with food and nutrition having an important role in its prevention and cause.
A new update to the Food, Nutrition, Physical Activity, and the Prevention of Colorectal Cancer Report by the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) as part of the Continuous Update Project (CUP) has just been published, including an additional 263 new articles from cohort studies and randomised controlled trials. The CUP provides a comprehensive and up-to-date systematic review of scientific developments on the relationship between diet, physical activity, obesity and cancer, with the panel consisting of leading scientists in these fields.
In this new report, the CUP panel agreed that the evidence for a protective effect from foods that contain dietary fibre had strengthened from probable in the previously completed Secondary Expert Report (SER) and therefore the evidence has been upgraded to ‘convincing’. This is highest level of evidence set by the WCRF and AICR, which identifies a causal relationship between a particular aspect of food, nutrition, physical activity or body composition, and cancer.
Twelve new papers were included in the review that investigated total dietary fibre and fibre from cereals, wholegrains, legumes, fruit and vegetables. The new report found that 13 of the 18 studies showed a decreased risk for colorectal cancer with increased intake of total dietary fibre.
The new meta-analyses showed a 10 per cent decreased risk for colorectal cancer and 11 per cent decreased risk for colon cancer with an increase in dietary fibre of 10g/day, which is a slightly better risk reduction than the 2007 report. The updated meta-analyses for rectal cancer, trended in the direction of decreased risk, but did not reach statistical significance.
Likewise, the updated reviews for sources of fibre and colorectal cancer showed a 10 per cent decreased risk for cereal fibre, but estimates for other sources of fibre were in the direction of decreased risk, but again did not reach statistical significance.
With 3 servings of wholegrains per day there was a 21 per cent decreased risk for colorectal cancer and 16 per cent decreased risk for colon cancer. There was also convincing evidence that physical activity protects against colon cancer. It is interesting to note the review concluded there is probable evidence that consumption of garlic, milk, and calcium may also protect from colorectal cancer.
The way in which fibre helps reduce the risk of colorectal cancer is due to several effects in the gastrointestinal tract, but the precise mechanism is still yet to be fully understood. Fibre dilutes faecal content, decreases transit time and increases stool weight whilst healthy gut bacteria from a wide range of dietary carbohydrates that reach the colon produce fermentation products, particularly short-chain fatty acids such as butyrate which helps to maintain healthy colon cells. Fibre intake is strongly correlated with intake of folate, however, adjusting for this does not often affect the risk reduction attributed to fibre.
The latest evidence from the WCRF review report also shows that consumption of red meat and processed meat, ethanol from alcoholic drinks (by men and probably by women), as well as body fatness and abdominal fatness, the factors that lead to greater adult attained height, or its consequences are convincing or probable causes of colorectal cancer.
Australian healthy eating guidelines recommend we eat at least 4 serves of core grain-based foods a day such as breads, breakfast cereals, rice, pasta and noodles, preferably wholegrain. One serve is equal to 2 slices of bread, approx 1 cup of breakfast cereal, 1 cup of cooked rice/noodles/pasta/oats. Don’t forget legumes are also a great source of fibre. Aim for at least 2 serves per week, 4 serves or more is even better for improved health outcomes. One serve is equal to half a cup of cooked dried beans, lentils, chickpeas etc.
WCRF/AICR World Cancer Research Fund / American Institute for Cancer Research.Continuous Update Project Interim Report Summary.Food, Nutrition, Physical Activity, and the Prevention of Colorectal Cancer. 2011