Poor Fitness Linked to Mitochondrial Problems

Twin study finds association between obesity, mitochondrial oxidative phosphorylation

MONDAY, June 23 (HealthDay News) -- Obesity is associated with poorer physical fitness, decreased insulin sensitivity, and decreased expression of mitochondrial genes involved in oxidative phosphorylation, independent of genetic factors, according to the results of a twin study released online May 6 in advance of publication in the American Journal of Physiology - Endocrinology and Metabolism.

Linda Mustelin, of the Helsinki University Central Hospital in Finland, and colleagues analyzed data from 14 identical twin pairs in which the siblings had discordant body mass index (BMI) status, and 10 pairs in which the twins had similar BMI status. The researchers assessed subjects' whole body insulin sensitivity, transcript profiles of mitochondrial genes from adipose samples, and maximal oxygen uptake and working capacity.

Obese subjects had lower insulin sensitivity than their non-obese twins, and the genes involved in the mitochondrial oxidative phosphorylation pathway were downregulated compared with the non-obese twins. They also had lower VO2max and maximal working capacity, and were less active as assessed by a leisure-time activity index.

"Although we found that the reduced transcript levels of genes encoding mitochondrial oxidative phosphorylation in obesity is influenced by environmental and acquired factors, it does not exclude the possibility that genetic factors contribute to regulation of mitochondrial oxidative metabolism, as has been shown for VO2max, physical activity and the VO2max response to physical training. The heritability estimates for VO2max vary between 50 percent and 67 percent in the two most recent studies," the authors write.

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