In September 2018 researchers from Japan published the results of their study to assess the effects of white rice and white bread on gut microbiota. A total of 7 healthy individuals completed two 1-week periods of consuming either white rice or white bread with the same selection of meals with a 1-week break in between. Fasting blood samples, breath samples, and faecal samples were collected at both the start and end of the study periods. Results showed that after the period of eating bread, the faecal Bifidobacterium genus, fasting glucagon-like peptide 1, and breath hydrogen were significantly higher than the levels following the period when rice was eaten instead. The level of short chain fatty acids also tended to be higher after the bread period. White bread contained more dietary fibre than refined short grain rice.
Mano F et al. The Effect of White Rice and White Bread as Staple Foods on Gut Microbiota and Host Metabolism. Nutrients. 2018 Sep 18;10(9). pii: E1323.