Fasting for 72 h increases intramyocellular lipid content in nondiabetic, physically fit men.

The purpose of this study was to determine changes in intramyocellular lipid (IMCL) content in the vastus lateralis of nondiabetic, physically fit males over 72 h of fasting. Six men, mean age 35 yr (range 23-55 yr), body mass index 23.7 kg/m2 (21.2-27.4 kg/m2), undertook a water-only fast for 84 h. Vastus lateralis IMCL content was determined using proton magnetic resonance spectroscopy after 12 and 84 h of fasting. Venous blood was sampled at 12-h intervals throughout the fast. IMCL-(CH2)n/water and IMCL-(CH2)n/total creatine ratios increased from 0.00623 +/- 0.00065 to 0.0142 +/- 0.0015 (P = 0.002) and 6.82 +/- 0.87 to 14.96 +/- 1.73 (P = 0.001), respectively. Plasma free fatty acid (FFA), serum triglyceride, and whole blood 3-hydroxybutyrate concentrations increased (P < 0.001, <0.05, <0.03, respectively), whereas plasma glucose and serum insulin concentrations decreased (both P < 0.001) during fasting. In conclusion, 72-h water-only fasting produces a large increase in plasma FFA concentration, a drop in serum insulin concentration, and accumulation of IMCL in the vastus lateralis muscle of nondiabetic, physically fit men.