Despite their popularity, potatoes have a reputation for being an unhealthy food that is high in starchy carbohydrates. Work from the lab of Dr. Thomas Schmidt of the University of Michigan, however, offers some redemption for the humble potato. While potatoes are high in easily digestible starch that can lead to blood sugar spikes, they are also high in resistant starch – a type of fiber that is “resistant” to digestion by human enzymes. Instead of being broken down by our body’s digestive enzymes, resistant starches are broken down by members of the gut microbiota, leading to the production of chemicals, such as butyrate, which are known to be good for our health.

The objective of the study led by Dr. Schmidt and his team was to compare the ability of different resistant starches to effect butyrate levels in the gut. To do this, the team recruited 174 healthy university students who were instructed to not modify their diets during the study other than by increasing their resistant starch intake through a dietary supplement. Although the authors recognize that different diets have an impact on the composition of the gut microbiota, this study allowed them to examine how the addition of resistant starch affects a normal diet.

The team compared the effect of digestible corn starch (the control group) to the effect of resistant starch from potatoes, resistant starch from maize, and inulin from chicory root. In the end, resistant starch from potatoes led to the greatest increase in butyrate compared to the other resistant starches tested. All of the resistant starches had an effect on the composition of the gut microbiota, but authors highlight that changes in the gut microbiota do not always translate to increased production of butyrate. It turns out that butyrate-producing bacteria depend on the action of other species of bacteria known as “primary degraders” to complete the first step of digestion before they can produce butyrate. The number of primary-degrading bacteria residing in the guts of participants at the beginning of the study affected the amount of butyrate that their gut microbiota produced in response to the resistant starch.

This study emphasizes that diverse and healthy gut microbiota is essential for realizing the health benefits of resistant starch consumption, and at this time, a varied and balanced diet is still the best way to ensure a similarly varied and balanced gut microbiota.