7th June 2017

A number of papers today cover a new study comparing the health effects of white bread versus wholegrain sourdough bread.

The study was a randomised crossover trial in 20 healthy subjects that compared the effects of consuming white bread for one week, followed (after a washout period) by consuming wholegrain sourdough for one week, or vice versa. Subjects were asked to have the equivalent of 3-4 slices for breakfast and then to have additional bread throughout the day and were told not to consume any other wheat-based products like other breads that were not included in the study or pasta.  

The researchers were expecting to see differences in the rise in blood sugar after the participants consumed the white bread versus the wholegrain sourdough bread and they also looked to see if subjects’ gut flora changed. However, they didn’t find any differences in either case when comparing consumption of the white and wholegrain breads.

 What they did find was that people’s individual responses to the bread, in terms of glycaemic response, varied much more than they expected and in some cases was opposite to what they would have predicted from the Glycaemic Index values of the bread, i.e. some people had a higher glycaemic response to the wholegrain bread than the white bread. 

The researchers looked at whether these differences could be linked to differences in gut flora and found that there did appear to be a relationship between the two and suggest that in future this should be taken into account when giving dietary advice. 

While these results are interesting, this work is at a very early stage and more research using bigger trials would be needed to confirm the results. This was a very small study of short duration and so the findings need to be interpreted with caution. The study didn’t do any in-depth measures of dietary intakes and so it’s not possible to look at whether other dietary factors could have affected results. In addition, the subjects ate a fairly large quantity of bread, which may not be a realistic dietary pattern.

 In practice most people have no way of knowing the composition of their gut flora and so wouldn’t be able to make food choices based on this. Choosing wholegrain bread and other wholegrain foods, as recommended in the Eatwell Guide, is important as fibre intakes are well below the recommendation of 30g per day.