The bi-phasic feeding pattern used in Experiment 2 resulted
in pigs having a greater proportion of muscle (2.8%) and a lower
proportion of fat (2.6%) than for pigs fed ad libitum. This
improved nutrient utilisation may also be a response to the
difference in insulin status for these two treatment groups.
Studies in growing animals have shown that the release of
insulin and amino acids after a meal plays a pivotal role in the
stimulation of skeletal muscle protein synthesis (Garlick et al.
1983; Davis et al. 1996; O’Connor et al. 2003; Orellana et al.
2006). Studies in neonatal pigs have shown that elevated
concentrations of circulating insulin, similar to those found in
fed animals, are required for the phosphorylation of skeletal
muscle insulin receptors and the stimulation of protein
synthesis (Suryawan et al. 2004). In addition, studies in older
animals have also shown that amino acids act independently or
in conjunction with infused insulin to stimulate protein synthesis
and act as primary regulators of protein synthesis in skeletal
muscle (Bennet et al. 1990; Giordano et al. 1996; Volpi et al.
1998). A specific threshold in insulin concentration appears to
be necessary to initiate protein synthesis. Studies in humans by
Cahill (1971) have shown that concentrations of insulin greater
than 10mU/mL are required for both lipogenesis and protein
synthesis. Therefore, a bi-phasic feeding regimen, where the
circulating insulin concentrations exceed this value, may be
instrumental in the stimulus of protein synthesis.