Proeyen, K. V., Deldique, L., Nielens, H., Szlufcik, K., & Hespel, P. (2010). Effects of training in the fasted state in conjunction with fat-rich diet on muscle metabolism. Presentation 721 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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"A high turnover rate of intramyocellular lipids (IMCL) is proposed to reduce high-fat diet-induced accumulation of toxic lipid intermediates interfering with insulin action. It has been shown that an acute exercise bout in the fasted state stimulates IMCL breakdown compared with postprandial exercise."

This study compared the effect of an exercise training program in the fasted state versus the postprandial state on insulin sensitivity and intramyocellular lipid content during a period of hypercaloric fat-rich diet, and to explore the underlying cellular mechanisms.

Moderately active males consumed a hyper-caloric (normal diet +30% kcal/day) high-fat (50%) diet during six weeks, alone (control; N = 7) or in conjunction with endurance training (1-1.5h @70% VO2max, four days per week) in either a fasted state (N = 10) or with carbohydrate intake before and during exercise (N = 10). Needle biopsies were taken from medial vastus lateralis. Glucose tolerance was measured by a two-hour oral glucose tolerance test.

In the control group, body weight increased by ~3kg. This weight gain was largely, if not entirely accounted for by fat accretion as evidenced by the 15% increase in sum of skinfolds, reflecting elevated subcutaneous fat deposit. The high-fat diet induced increase in body weight and skinfolds largely negated by training in a fasted state. Compared with the controls, both glucose tolerance and whole-body insulin sensitivity were improved after training in a fasted state, but not in the carbohydrate state. The high-fat diet increased intramyocellular lipid content to the same degree in all groups in both type I and type IIa fibers. Muscle diacylglycerol, ceramide, and phospholipid content were not significantly different between the groups at any time. The training-induced upregulation (+28%) of muscle GLUT4 content was greater in the fasting condition than in the carbohydrate condition. Furthermore, compared with the control, the phosphorylated fraction of AMPKa increased by ~25% in the fasting group but not in the carbohydrate group. Endoplasmatic reticulum stress occurred only in the fasting group, as indicated by elevated protein content of the unfolded protein response markers IRE1a and BiP.

Implication. Exercise training in the fasted state during a period of high-fat diet is more effective than similar training in the carbohydrate-fed state to promote metabolic adaptations in muscles that enhance glucose tolerance and insulin action.

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