Fat content in individual muscle fibers of lean and obese subjects

Abstract

OBJECTIVE: To examine skeletal muscle intracellular triglyceride concentration in different fiber types in relation to obesity. DESIGN: Skeletal muscle fiber type distribution and intracellular lipid content were measured in vastus lateralis samples obtained by needle biopsy from lean and obese individuals. SUBJECTS: Seven lean controls (body mass index (BMI) 23.0 AE 3.3 kg=m 2 ; mean AE s.d.) and 14 obese (BMI 33.7 AE 2.7 kg=m 2 ) individuals; both groups included comparable proportions of men and women. MEASUREMENTS: Samples were histochemically stained for the identification of muscle fiber types (myosin ATPase) and intracellular lipid aggregates (oil red O dye). The number and size of fat aggregates as well as their concentration within type I, IIA and IIB muscle fiber types were measured. The cellular distribution of the lipid aggregates was also examined. RESULTS: The size of fat aggregates was not affected by obesity but the number of lipid droplets within muscle fibers was twice as abundant in obese compared to lean individuals. This was seen in type I (298 AE 135 vs 129 AE 75; obese vs lean, P < 0.05), IIA (132 AE 67 vs 79 AE 29; P < 0.05), and IIB (103 AE 63 vs 51 AE 13; P < 0.05) muscle fibers. A more central distribution of lipid droplets was observed in muscle fibers of obese compared to lean subjects (27.2 AE 5.7 vs 19.7 AE 6.4%; P < 0.05). CONCLUSION: The higher number of lipid aggregates and the disposition to a greater central distribution in all fiber types in obesity indicate important changes in lipid metabolism and=or storage that are fiber type-independent.

Effect of diet-induced obesity and metabolic syndrome on skeletal muscles of Ossabaw miniature swine

“…Similar findings were previously reported for Biceps muscles of Yucatan swine on a "Western"-type diet (14). These data correlate well with previous studies in humans showing that skeletal muscles from obese compared with lean individuals have greater muscle CSAs (9,24). The increased CSAs could have a negative effect on the oxygen and substrate supply to the center of the fiber, leading to the reduced muscle performance.…”

“…Increased fiber size could diminish oxygen and substrate supply for the metabolic processes in the central area of the fiber. Skeletal muscles from obese compared with lean individuals had greater muscle cross-sectional areas (CSAs) of both type 1 and 2 fibers (9,24). Weight loss resulted in a 14 -25% decrease of the fiber CSAs of both type 1 and type 2 muscle fibers (12), supporting the idea that obesity correlates with an increase in muscle fiber area.…”

“…Lillioja et al (22) showed that in vivo insulin action determined by the euglycemic clamp was positively correlated with the percentage of type 1 fibers and negatively correlated with the percentage of type 2b/x fibers in vastus lateralis muscles of humans. Several studies showed that obese individuals with or without type 2 diabetes had a significantly lower percentage of type 1 and a higher percentage of type 2b/x muscle fibers than lean individuals (2,10,17,24,25,29,35).…”

“…Muscle lipid content followed the order of type 1 Ͼ type 2a Ͼ type 2b/x, but, within each fiber type, skeletal muscle from obese and NIDDM women and men had greater lipid content than muscle from lean subjects (16,24). The size of lipid aggregates was not affected by obesity, but the number of lipid droplets within muscle fibers was two times as abundant and had a more central distribution in obese compared with lean individuals (24). Weight loss results in the decreased IMCL content (11,12).…”

Lipotoxicity: the obese and endurance-trained paradox

“…In both obese and lean subjects, it has been shown that the IMTG content is the greatest in the oxidative type I and the lowest in the glycolytic type II muscle fibres. 34 Interestingly, it is the oxidative type I fibres which are the most insulin sensitive. 35 When comparing the divergent conditions of obesity and ETr, an apparent inconsistency exists in the relationship between IMTG and insulin sensitivity.…”