Dietary feeding pattern does not modulate the loss of muscle mass or the decline in metabolic health during short-term bed rest

This is the author accepted manuscript. The final version is available from the American Physiological Society via the DOI in this record.Short periods of bed rest lead to the loss of muscle mass and quality. It has been speculated that dietary feeding pattern may impact upon muscle protein synthesis rates and, therefore, modulate the loss of muscle mass and quality. We subjected 20 healthy men (age: 25±1 y, BMI: 23.8±0.8 kg·m-2) to one week of strict bed rest with intermittent (4 meals/day) or continuous (24 h/day) enteral tube feeding. Participants consumed deuterium oxide for 7 days prior to bed rest and throughout the 7-day bed rest period. Prior to and immediately after bed rest, lean body mass (DXA), quadriceps cross-sectional area (CSA; CT), maximal oxygen uptake capacity (VO2peak), and whole-body insulin sensitivity (hyperinsulinaemic-euglycaemic clamp) were assessed. Muscle biopsies were collected 7 days prior to, 1 day prior to, and immediately after bed rest to assess muscle tracer incorporation. Bed rest resulted in 0.3±0.3 vs 0.7±0.4 kg lean tissue loss and a 1.1±0.6 vs 0.8±0.5% decline in quadriceps CSA in the intermittent vs continuous feeding group, respectively (both P0.05). Moreover, feeding pattern did not modulate the bed rest-induced decline in insulin sensitivity (-46±3% vs 39±3%; P0.05). Myofibrillar protein synthesis rates during bed rest did not differ between the intermittent and continuous feeding group (1.33±0.07 vs 1.50±0.13%·d−1, respectively; P>0.05). In conclusion, dietary feeding pattern does not modulate the loss of muscle mass or the decline in metabolic health during one week of bed rest in healthy men

Tumour‐specific and organ‐specific protein synthesis rates in patients with pancreatic cancer

Background: Living tissues maintain a fine balance between protein synthesis and protein breakdown rates. Animal studies indicate that protein synthesis rates are higher in organs when compared with skeletal muscle tissue. As such, organ and tumour protein synthesis could have major effects on whole‐body protein metabolism in wasting disorders such as cancer cachexia. We aimed to assess protein synthesis rates in pancreatic tumour tissue and healthy pancreas, liver, and skeletal muscle tissue in vivo in humans. Methods: In eight patients with pancreatic cancer undergoing pancreaticoduodenectomy, primed continuous infusions with L‐[ring‐13C6]phenylalanine and L‐[3,5‐2H2]tyrosine were started prior to surgery and continued throughout the surgical procedures. During surgery, plasma samples and biopsies from the pancreas, pancreatic tumour, liver, and vastus lateralis muscle were taken. Post‐absorptive fractional protein synthesis rates were determined by measuring incorporation of labelled L‐[ring‐13C6]phenylalanine in tissue protein using the weighed plasma L‐[ring‐13C6]phenylalanine enrichments as the precursor pool. Results: Five male patients and three female patients with a mean age of 67 ± 2 years were included into this study. Plasma L‐[ring‐13C6]phenylalanine enrichments (6–9 mole per cent excess) did not change during surgery (P = 0.60). Pancreatic tumour protein synthesis rates were 2.6‐fold lower than surrounding pancreatic tissue protein synthesis rates (0.268 ± 0.053 vs. 0.694 ± 0.228%/h, respectively; P = 0.028) and 1.7‐fold lower than liver protein synthesis rates (0.268 ± 0.053 vs. 0.448 ± 0.043%/h, respectively; P = 0.046). Among healthy organ samples, protein synthesis rates were 20‐fold and 13‐fold higher in pancreas and liver, respectively, compared with skeletal muscle tissue (0.694 ± 0.228 and 0.448 ± 0.043 vs. 0.035 ± 0.005%/h, respectively; P < 0.05). Conclusions: Liver and pancreas tissue protein synthesis rates are higher when compared with pancreatic tumour and skeletal muscle tissue protein synthesis rates and can, therefore, strongly impact whole‐body protein metabolism in vivo in humans