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The letter P brings together two of the most talked about supplement families: proteins, which have been perennially popular since the time of the ancient Olympians and prohormones, which will be dealt with in a later issue. Both supplement families include products which range from simple and relatively inexpensive, to exotic, expensive and emotively marketed. Part 32 also includes information on proline, a non-essential amino acid which is marketed for growth and repair of soft tissue based on its importance in the make-up of collagen.
S M Phillips L Breen
Skeletal muscle protein turnover rates are ∼1%–2%/d and exist in dynamic, usually balanced, equilibrium between muscle protein breakdown (MPB) and muscle protein synthesis (MPS). For example, in the fasted state, MPB>MPS, whereas in response to ingestion of protein-containing meals, MPS>MPB.1 Thus, in healthy adults, muscle mass remains relatively stable due to ‘fed-gain’ being balanced by fasted-loss, so daily protein flux, while it may be 3–4 times greater than net intake and loss, is in tight balance. Fasted-state protein losses are typically about 40–60 g/d for a sedentary person weighing 70–90 kg and it is debatable what the losses would be in athletes, be they aerobically or resistance trained. Dietary protein for athletic populations can serve as signal and substrate for MPS, resulting in protein accretion for hypertrophy, repair of damaged proteins or assisting the maintenance of lean mass. There are important messages for athletes, who differ from sedentary individuals, in terms of quantity, timing and quality of protein intake in relation to an athlete's training stimulus. The molecular changes underpinning these adaptations are gene transcription and mRNA translational signalling and are highlighted in a review.2
The general consensus is that adults need no more than 0.8–0.9 g/kg/d of protein to meet their needs. However, the notion of consumption of ‘extra’ protein above these …
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