Intense exercise alters the balance of bacteria and important compounds in the digestive system of athletes.[1][2] A German study from the University of Tübingen followed 150 people who had not previously exercised during an eight-week weight training program with two to three workouts per week.[1][2] Participants used either lighter weights for 15 to 20 repetitions or heavier weights for 8 to 10 repetitions, resulting in improvements in strength and body composition.[2] In people with a high response to training, there was an increase in 16 types of intestinal bacteria and a decrease in 11 others, and two new species were added.[2] Bacteria producing short-chain fatty acids increased, although their levels in stool samples did not increase.[1] When the training load decreased, the quality of the diet decreased and digestion slowed down, causing microbial changes. These changes can affect the performance of athletes.[4]