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Title: The effects of age, meal size and protein quality on protein utilisation in adult humans
Author: Fereday, Amelia Clare
ISNI:       0000 0001 3459 9291
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1995
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The studies described in this thesis were designed to evaluate the efficiency of postprandial protein utilisation (PPU) especially in relation to ageing, protein quality and meal size. The methodology for the quantitation of the efficiency of PPU was developed using a 9 hour leucine constant intravenous infusion. This protocol consisted of 3, 3 hour phases: the postabsorptive state; frequent feeding of small, low protein meals and frequent feeding of small, high protein meals. Using this protocol milk protein was fed to a group of 25 adults (aged 19-90 years). Dietary energy, via its influence on insulin secretion, exerted a protein conserving effect by inhibiting proteolysis and to a lesser extent protein synthesis. The addition of protein to the diet had an anabolic effect, enhancing the insulin-mediated inhibition of proteolysis and stimulating protein synthesis. Milk protein appeared to be utilised with a near 100% efficiency, any variation reflecting mainly the degree to which proteolysis was inhibited by insulin and dietary amino acids. In the elderly subjects (n=10, >65 yrs) PPU was not significantly different from younger age groups. However in a subgroup of 4 elderly PPU was lower due to a reduction in the amino acid sensitivity of proteolysis. Although this subgroup had no significant difference in their lean body mass it may be that the reduced PPU values indicate a risk of development of loss of lean body mass and hence they may require higher habitual protein intakes to ensure optimal postprandial protein deposition. The influence of protein quality on PPU was examined in 5 subjects by comparing the utilisation of wheat protein with milk. The PPU for wheat protein was less than that observed for milk (67% efficient), but greater than would be predicted from its amino acid composition and the currently recommended scoring pattern. The reason for this was a lower inhibition of proteolysis with wheat compared with milk, possibly because of the lower leucine concentration in wheat protein. The effect of meal size on PPU was examined by measuring leucine balance following a single meal of milk or wheat protein. The values of PPU obtained were similar to the small meal values (i.e. 60% wheat, 94% milk). Non steady state calculations indicated that milk protein was deposited by an inhibition of proteolysis with little change in protein synthesis while the wheat protein was deposited by a combination of a reduction in proteolysis and a stimulation of protein synthesis. Thus postprandial protein utilisation is i) reduced in some otherwise healthy elderly adults, ii) is lower for wheat than for milk protein and iii) is not influenced markedly by meal size.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nutrition