Updated: Sep 14, 2021
The largest microbiome study (the American Gut Project) to date tested over 11 000 stool samples alongside dietary and lifestyle questionnaires and observed that the largest predictor of a diverse microbiome (associated with favourable health outcomes) was diet diversity, in particular a diversity of plant foods.
Those who consumed more than 30 different plant foods per week also had reduced antibiotic resistance. This may partly be due to the association between reduced plant consumption and increased meat intake from antibiotic treated animals. (McDonald et al., 2018)
This study additionally observed that those who reported mental illness, including anxiety, depression, schizophrenia and OCD, had an altered microbiome with specific species elevated and others absent/reduced.
So how does a variety of plant foods improve the microbiome?
· Different fibres feed different species of gut microbes!
· When we consume fibre our gut microbes produce compounds including short chain fatty acids which improve the integrity of our gut lining, can reduce inflammation, improve our immune response and much more.
· A variety of plant foods contain different polyphenols which can both feed beneficial microbes and inhibit pathogenic species.
Resistant starch is a type of fibre which resists digestion and instead acts as a substrate for butyrate production by our gut microbes!
Resistant starch can improve the integrity of the gut wall, promote a healthy gut mucus membrane, regulate the immune system (reducing inflammation), modulate blood sugar and blood cholesterol levels and reduce risk of conditions including colon cancer, constipation, diverticulosis, haemorrhoids and inflammatory bowel disease.
Foods rich in resistant starch include green bananas, legumes, cooked and cooled potato/sweet potato and cooked and cooled rice (adding 1tsp of coconut oil when cooking increases resistant starch formation).
McDonald, D., Hyde, E., Debelius, J. W., Morton, J. T., Gonzalez, A., Ackermann, G., Aksenov, A. A., Behsaz, B., Brennan, C., Chen, Y., DeRight Goldasich, L., Dorrestein, P. C., Dunn, R. R., Fahimipour, A. K., Gaffney, J., Gilbert, J. A., Gogul, G., Green, J. L., Hugenholtz, P., … Gunderson, B. (2018). American Gut: an Open Platform for Citizen Science Microbiome Research. MSystems, 3(3). https://doi.org/10.1128/msystems.00031-18