Oleate-enriched diet improves insulin sensitivity and restores muscle protein synthesis in old rats

Background & aims: Age-related inflammation and insulin resistance (IR) have been implicated in the inability of old muscles to properly respond to anabolic stimuli such as amino acids (AA) or insulin. Since fatty acids can modulate inflammation and IR in muscle cells, we investigated the effect of palmitate-enriched diet and oleate-enriched diet on inflammation, IR and muscle protein synthesis (MPS) rate in old rats. Methods: Twenty-four 25-month-old rats were fed either a control diet (OC), an oleate-enriched diet (HFO) or a palmitate-enriched diet (HFP) for 16 weeks. MPS using labeled amino acids and mTOR activation were assessed after AA and insulin anabolic stimulation to mimic postprandial state. Results: IR and systemic and adipose tissue inflammation (TNF alpha. and IL1 beta) were improved in the HFO group. Muscle genes controlling mitochondrial beta-oxidation (PPARs, MCAD and CPT-1b) were up-regulated in the HFO group. AA and insulin-stimulated MPS in the HFO group only, and this stimulation was related to activation of the Akt/mTOR pathway. Conclusions: The age-related MPS response to anabolic signals was improved in rats fed an oleate-enriched diet. This effect was related to activation of muscle oxidative pathways, lower IR, and a decrease in inflammation. (C) 2011 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.