Elevated intramyocellular lipid concentration in obese subjects is not reduced after diet and exercise training

To determine the effects of weight loss on intramyocellular energy substrat es, vastus lateralis muscle biopsies were taken from six obese subjects (bo dy mass index 34 +/- 5 kg/m(2)) before, after 15 wk of energy restriction ( ER; -700 kcal/day), and after a further average 20.7 +/- 1.6 wk of enduranc e training plus low-fat diet (ET-LFD). Body weight fell from 100 +/- 6 to 8 9 +/- 6 kg during ER and to 84 +/- 4 kg after ET-LFD. Lipids and glycogen w ere histochemically measured in type I, IIA, and IIB fibers. Total muscle g lycogen content (MGC; per 100 fibers) decreased after ER [from 72 +/- 13 to 55 +/- 8 arbitrary units (AU)]. A similar but not significant decrease was seen in total muscle lipid content (MLC; 14 +/- 5 to 9 +/- 1 AU). After ET -LFD, MGC returned to initial values (74 +/- 8 AU), and MLC approached near -initial values (12 +/- 3 AU). Individual fiber lipid concentration did not change throughout the protocol in all fiber types, whereas glycogen concen tration increased after ET-LFD. The training effects of ET-LFD were measure d as increasing activities of key mitochondrial enzymes. Although total mus cle energy reserves can be reduced after weight loss, their concentration w ithin individual myofibers remains elevated. Weight loss does not appear su fficient to correct the potential detrimental effects of high intracellular lipid concentrations.