Effects of intermittent fasting or calorie restriction on markers of lipid metabolism in human skeletal muscle.

CONTEXT Impaired lipid metabolism is linked with obesity-associated insulin resistance, which may be reversed by caloric restriction (CR). OBJECTIVE In a secondary analysis of a randomized controlled trial, we compared the effects of intermittent fasting (IF) and CR on markers of lipid metabolism in muscle. DESIGN Seventy-six women (BMI 25-40 kg/m2) were randomized to one of three diets for eight weeks and provided with foods at 70% (CR70 and IF70) or 100% (IF100) of energy requirements. IF groups ate breakfast, prior to a 24-hour fast on 3 non-consecutive days per week. On non-fasting days, IF70 ate at 100% and IF100 ate at 145% of energy requirements to achieve the prescribed target. Weight, body composition, insulin sensitivity by clamp, non-esterified fatty acids (NEFA), β-hydroxybutyrate, and markers of lipid metabolism and oxidative stress in muscle by qPCR were measured at baseline and week 8 following a 12-hour overnight fast (all groups) and 24-hour fast (IF groups). RESULTS IF70 resulted in greater weight and fat losses and reduced NEFA versus CR70 and IF100 after an overnight fast. IF70 and IF100 induced a greater reduction only in mRNA levels of antioxidant enzymes  GPX1, SOD1 and SOD2 versus CR70. Fasting for 24-hours increased NEFA and β-hydroxybutyrate in IF groups, but impaired insulin sensitivity and increased PLIN5 mRNA levels. CONCLUSIONS In comparison to CR, IF did not increase markers of lipid metabolism in muscle, but reduced expression of antioxidant enzymes. However, fasting-induced insulin resistance was detected, alongside increased PLIN5 expression, potentially reflecting transient lipid storage.