High-fat diet overrules the effects of training on fiber-specific intramyocellular lipid utilization during exercise

A hypercaloric fat-rich diet increased intramyocellular lipid content by 50% in type I and 75% in type IIa muscle fibers.

• Endurance training in either a fasted or fed state did not significantly alter the net breakdown of muscle glycogen during exercise.
• A hypercaloric fat-rich diet, regardless of training state, led to a twofold increase in exercise-induced net intramyocellular lipid breakdown in type I fibers.
• Type IIa fibers experienced approximately fourfold increased net intramyocellular lipid breakdown during exercise when on a hypercaloric fat-rich diet.
• The control group that did not undergo training gained about 3 kg in body weight after the hypercaloric diet.
• The study indicates that a hypercaloric fat-rich diet supports high muscle glycogen content without impairing muscle glycogen breakdown during exercise.

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