Health benefits associated with wholegrains may be, in part, due to their prebiotic effect. This is the conclusion of a 3-week intervention study conducted by UK scientists at Reading.

Many observational studies have linked whole-wheat consumption with a lower risk of cancer and heart disease. The health effects were thought to be due to fibre or the vitamin and minerals present in wholegrains. Now an intervention study has raised the possibility that wholegrain cereals could be producing a prebiotic effect. Prebiotics are non-digestible fibres that pass through the small intestine unchanged, reaching the colon, where they are fermented by ‘beneficial’ bacteria, such as lactobacillus and bifidobacteria, stimulating the growth of these beneficial bacteria. Consumption of prebiotic-rich foods has been linked with a lower risk of bowel cancer and other gut diseases, and lower cholesterol levels.

Healthy volunteers (n=31) were randomly assigned to one of two groups and asked to consume 48g of breakfast cereal daily for 3 weeks. The first group consumed a wholegrain cereal, while the second group consumed a cereal rich in wheat bran. After a two-week washout period (normal diet), the groups swapped over and repeated the study protocol. Various tests were done at baseline and after the cereal interventions, e.g. measuring levels of gut bacteria in faeces, fasting blood cholesterol levels, blood sugar levels, genotoxicity of faeces (indicating bowel cancer risk).

The results showed that faecal levels of ‘beneficial’ bacteria were higher after wholegrain consumption compared with wheat bran consumption. This suggests that the wholegrain cereal was having a prebiotic effect. However, there were no significant changes in the other measures taken. Given that no health benefits were found in this study, more research is needed to confirm whether wholegrain cereals are truly prebiotic.

For more information, see
Costabile A et al (2007). Whole-grain wheat breakfast cereal has a prebiotic effect on the human gut microbiota: a double-blind, placebo-controlled, crossover study. British Journal of Nutrition, e-publication, 29^th August.

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