HbA1c and Liver Fat Following 16 Weeks of Fasted versus Fed Exercise Training in Adults with Type 2 Diabetes

Purpose Exercise-nutrient timing is of interest for people with type 2 diabetes (T2D) as a potential method to optimize glycemic control. However, the optimal nutritional environment for exercise is not well understood over the long term. The Fasted Exercise for Type 2 Diabetes (FED) Trial compared 16 weeks of fasted versus postprandial morning exercise on glycated hemoglobin (HbA1c) and liver proton density fat fraction (PDFF). Methods Twenty adults with T2D were recruited and randomized to complete exercise after an overnight fast versus after their morning meal. Participants walked three mornings per week, progressing to 180 minutes per week over 16 weeks. Results Groups were balanced with 5 males and 5 females each. Sixteen participants completed the trial (8 in each group, 50% female). Age, HbA1c, and PDFF were 59.8 ± 9.0 years, 7.2 ± 0.7%, and 9.3 ± 4.1%, respectively. On average, both groups completed 98% of their walking sessions but there was no change in HbA1c (-0.2%, p = 0.588). However, one participant from each group had changes in their glucose lowering medication during the trial and, when excluded, the fasted training group had greater improvements in HbA1c compared to the postprandial group (-0.3% versus 0.0%, p = 0.033). There was no difference in changes in liver PDFF between groups (-1.6% versus 0.3%, p = 0.221) but visceral fat and intramuscular fat decreased to a greater extent following fasted exercise. Conclusions Although our study had a small sample size, it suggests that exercise after an overnight fast can have high adherence and represents an option for people with T2D to improve longer-term indicators of glycemia and ectopic fat depots.