High-protein diets can affect the gut microbiome in a way that hinders endurance performance, a new study shows.5 UK researchers fed runners either high-protein or high-carb diets and found the high-protein group saw a disturbance in the stability of their gut microbiome, which was accompanied by a huge 23% reduction in time-trial performance. On the other hand, those put on a high-carb diet saw improvements in time trial performance of 6.5%.