SHR # 2784:: Beginning Your Fast With Aerobic Exercise - Dr. Bruce Bailey, PhD, FTOS, FACSM - Landon Deru PhD Student, M.S., M.B.A., A.T.C. - Completing aerobic exercise at the beginning of a fast accelerates the production of BHB throughout the fast without altering subjective feelings of hunger, thirst, stomach discomfort, or mood. Insulin and the insulin/glucagon ratio experience a marked reduction within the first 12 h of fasting and was not altered with exercise. Thus, exercising at the beginning of a fast may improve the metabolic outcomes of fasting.