Short-term effects of dietary fat on intramyocellular lipid in sprinters and endurance runners

The effect of short-term fat loading on intramyocellular lipid (IMCL) in different types of muscle in endurance runners and sprinters has not been fully elucidated yet. The purpose of this study was to investigate the effect of dietary lipid on IMCL in soleus muscle (SOL) and tibialis anterior muscle (TA) during training period in endurance runners and sprinters. Seven male endurance runners and 7 male sprinters were selected to participate in the study. We measured TA- and SOL-IMCL levels after 3-day course of isocaloric normal- (25%), high- (60%), and low-fat (10%) diet during training period by (1)H-magnetic resonance spectroscopy in each subject. In sprinters, TA- and SOL-IMCL levels were comparable after each diet protocol. However, in endurance runners, TA-IMCL levels after normal-fat and high-fat diets were 1.7 times and 3.0 times higher than that after low-fat diet, respectively. The SOL-IMCL values after normal-fat diet and high-fat diet were 1.5 times and 1.6 times higher than that after low-fat diet, respectively. In addition, the TA-IMCL level after high-fat diet, but not SOL-IMCL, was significantly higher compared with that after normal-fat diet. Our data suggested that short-term dietary fat challenge during training period significantly altered IMCL level in endurance runners, but not in sprinters. In addition, response to fat loading on IMCL was influenced by variation of muscle type in endurance runners. These phenotypic and regional differences might be explained by differences in type of exercise training and muscle fiber composition.