PREBIOTICS, PROBIOTICS AND BOWEL CANCER RISK

Eating yoghurt, and possibly taking a probiotic supplement, may reduce the risk of colorectal cancer, according to the findings of a new systematic review.
Prebiotic and probiotic supplements, and yoghurt (a food containing probiotics) can change the diversity of the gut microbiota, which in turn, may influence the risk of colorectal cancer.

Probiotics are live bacteria found in certain foods and supplements, which can provide particular health benefits. Prebiotics are the food for our good bacteria and include indigestible carbohydrates in certain foods, such as fibre, resistant starches and resistant sugars, which our digestive system can’t break down. Instead, they pass down into our large intestine, where they feed our beneficial bacteria. The bacteria in our gut break down prebiotics to form short-chain fatty acids (acetate, propionate and butyrate), which help to keep the lining of the gut healthy and have been associated with reduced inflammation, improved immunity and a reduced risk of bowel cancer.

A recent systematic review of 10 studies (7 prospective cohort studies, 2 case-control studies and 1 randomised controlled trial) looked at the effect of consuming probiotics and prebiotics on the incidence of colorectal cancer. Study participants were adults 18 years or older who didn’t have gastrointestinal disease when the studies began. The follow-up period in the studies ranged from 4 to 32 years.
The studies included the use of:

• Prebiotic supplements, including inulin, fructooligosaccharides, galactooligosaccharides, xylooligosaccharides, isomaltooligosaccharides, and β-glucans
• Probiotic supplements containing bacterial strains of Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Bacillus, Pediococcus, Leuconostoc, and Escherichia coli
• Synbiotic supplements, a mixture of both prebiotics and probiotics
• Yoghurt containing live microbes

Compared to those who ate little or no yoghurt, participants with a high consumption of yoghurt had a moderate decrease in the risk of adenoma and colorectal cancer. Colorectal adenomas are benign (non-cancerous) tumours, often called polyps, which are a precursor to bowel cancer.

The review also found some evidence that probiotic supplementation may be associated with a lower risk of adenomas, but not with the incidence of colorectal cancer. There was no association between prebiotic supplementation and colorectal cancer risk.

The researchers suggest that further research is needed to understand whether the association between yogurt and colorectal cancer is due to the probiotic bacteria in the yogurt or other nutritional components. For example, there is evidence that dairy foods and calcium may reduce colorectal cancer risk. They also point out that the study didn’t include prebiotic foods and probiotic foods other than yoghurt, which may have a different effect compared to supplements.

Foods containing prebiotics include legumes, oats, under-ripe bananas, Jerusalem artichokes, asparagus, garlic, onions and leeks. Other food sources of probiotics include fermented drinks, including kefir and kombucha, sauerkraut and kimchi (fermented cabbage), miso (fermented soybean paste) and some types of pickles and pickled vegetables.

Read more:

• Kim and colleagues. The Impact of Prebiotic, Probiotic, and Synbiotic Supplements and Yogurt Consumption on the Risk of Colorectal Neoplasia among Adults: A Systematic Review. Nutrients. 2022.
• World Cancer Research Fund. Colorectal cancer.

Dr Kate Marsh is an is an Advanced Accredited Practising Dietitian, Credentialled Diabetes Educator and health and medical writer with a particular interest in plant-based eating and the dietary management of diabetes and polycystic ovary syndrome (PCOS).

Contact: Via her website www.drkatemarsh.com.au