BACKGROUND We recently reported better wheat-protein utilization and a higher apparent lysine requirement than would be predicted, because of adaptive mechanisms of lysine conservation. However, such findings may be subject to the feeding protocol of frequent small meals. OBJECTIVE We used a [1-13C]leucine balance, large single-meal protocol to estimate the utilization of wheat and the consequent lysine requirements. DESIGN Wheat and milk utilization were compared in 5 adults infused for 9 h with L-[1-13C]leucine, in the postabsorptive (0-3 h) and postprandial (3-9 h) states after ingestion of a single meal of either milk (30.4 kJ/kg; 32% of energy as protein) or a mixture of wheat gluten and whole wheat (29.2 kJ; 26.7% of energy as protein). Premeal nitrogen balance was predicted from [1-13C]leucine oxidation and postmeal balance predicted from cumulative increased leucine oxidation, enabling evaluation of the metabolic demand for protein, the efficiency of postprandial protein utilization (PPU), and the requirements for wheat protein and lysine. RESULTS Mean (+/-SD) PPU was 0.61 +/- 0.03 and 0.93 +/- 0.02 for wheat and milk (P < or = 0.001), respectively, and the estimated average wheat-protein requirement (0.6 g.kg(-1).d(-1)/PPU) was 0.98 +/- 0.05 g.kg(-1).d(-1), indicating a lysine requirement of 18.3 +/- 1.0 mg. kg(-1).d(-1). CONCLUSIONS Measured wheat utilization efficiency at 0.61 was considerably higher than the value predicted from wheat lysine intake and milk protein lysine deposition (ie, 0.222 +/- 0.004). These results confirm our previous finding that lysine conservation allows wheat protein to be utilized more efficiently than expected and is consistent with a lysine requirement in fully adapted individuals of 19 mg.kg(-1).d(-1), as indicated by recalculated nitrogen balance data.

BACKGROUNDThere is considerable debate about the human lysine requirement and the consequent nutritional value of wheat protein.OBJECTIVEWe used a novel [1-(13)C]leucine balance protocol to examine whether adaptive mechanisms to conserve lysine allow wheat to be utilized more efficiently than expected according to current estimates of lysine requirements and wheat utilization.DESIGNWheat and milk proteins were compared in 6 adults infused for 9 h with L-[1-(13)C]leucine in the postabsorptive state (0-3 h), who were fed half-hourly with low-protein (2% of energy, 3-6 h) and isoenergetic higher-protein (12-13% of energy, 6-9 h) meals providing maintenance energy intakes. From acute measurements of [1-(13)C]leucine balance, we predicted nitrogen balance, the metabolic demand for protein, the efficiency of postprandial protein utilization (PPU), and the requirements for wheat protein and lysine.RESULTSLeucine balance was higher after the milk than after the wheat feeding because of the greater inhibition of proteolysis by milk. PPU, calculated as the ratio of Deltanitrogen balance to Deltanitrogen intake between the low-protein and higher-protein periods, was 0.68 +/- 0.06 for wheat and 1.00 +/- 0.09 for milk (P </= 0.001). The estimated average wheat protein requirement (0. 6/PPU) was 0.89 +/- 0.08 g*kg(-)(1)*d(-)(1), indicating a lysine requirement of 23.2 +/- 2.0 mg*kg(-)(1)*d(-)(1). The measured PPU for wheat, 0.68 +/- 0.06, was higher than the value calculated from wheat lysine intake and milk protein lysine deposition, 0.26 +/- 0. 02, and higher than predicted by most published estimates of lysine requirements, apart from a value of 19 mg/kg indicated by nitrogen balance studies.CONCLUSIONSThe results show that adaptive mechanisms of lysine conservation allow wheat protein to be utilized more efficiently than expected.

1. The variability between normal individuals in the efficiency of postprandial protein utilization (PPU), a determinant of the apparent protein requirement, was examined in relation to the relative responses of protein synthesis and proteolysis to protein feeding by means of [1-13C]leucine turnover and balance studies.2. Twenty-five healthy adults were infused intravenously with L-[1-13C]leucine continuously for 9 h. This was started in the postabsorptive state (PA, 3 h) and followed by low-protein feeding (LP, 3 h), and then by isoenergetic high-protein feeding (HP, 3 h). This allowed protein intake to be varied against a constant postprandial insulin level so that the extent of any amino-acid-mediated responses which were additional to those exerted by insulin could be investigated. Leucine oxidation, O, and balance (intake-oxidation), protein synthesis, S, and degradation, D, were calculated from plasma [1-13C]alpha-ketoisocaproic acid enrichment and 13CO2 excretion.3.PPUprotein, calculated as change in leucine balance/change in intake (HP-LP), varied from 0.58 to 0.99 (mean=0. 81+/-0.10), independently of age or sex. PPUprotein varied directly with the inhibition of D and inversely with the increase in leucine concentration and stimulation of O and S.4. Efficient PPU, as demonstrated by the top quintile of individuals categorized in terms of PPUprotein, involves maximal inhibition of D by protein feeding with minimal increases in free amino acid concentrations, O and S. Lesser inhibition of D and greater stimulation of S and O characterized the lower, less efficient quintile. This indicates that the efficiency of protein utilization in individuals, and a component of their apparent protein requirement, is determined by the sensitivity of the insulin-mediated inhibition of proteolysis to amino acid supply.

Current protein requirements for the elderly derive from 1985 FAO/WHO/UNU recommendations of no change with age in adults: i.e., 0.6 g/kg average and 0.75 g/kg safe allowance. Although concern has been expressed that protein requirements for the elderly may be greater, a review of nitrogen balance data, none of which are entirely satisfactory, indicates little reason for any revision. Furthermore, the 1985 recommendation is generally consistent with reports that the rate of whole-body protein turnover, a commonly assumed determinant of the protein requirement, exhibits minimal change with age per unit fat-free mass. Recent novel tracer studies aimed at evaluating protein requirements and turnover in a systematic way also support the 1985 recommendations. [1-13C]leucine balance studies have allowed measurement of metabolic demand from postabsorptive leucine oxidation and the efficiency of protein utilization from changes in leucine balance with feeding. The apparent protein requirement is metabolic demand divided by efficiency, an indication of protein needs and utilization during a standardized protocol at intakes similar to habitual ones. In healthy, mobile, elderly persons, metabolic demands are reduced by about one-third, with no significant impairment in efficiency of protein utilization. Thus, apparent protein requirements appear to fall with age from 0.98 +/- 0.17 to 0.69 +/- 0.22 g/kg. These changes with age reflect an improved restraint of proteolysis in the postabsorptive state, with little change with age in whole-body protein synthesis. The requirements of frail and immobile elderly and the efficiency of protein utilization of meals as eaten by elderly people remain to be evaluated.

The protein requirements of the elderly were investigated with [13C]leucine balance studies of metabolic demand, the efficiency of postprandial protein utilization (PPU) and the consequent apparent protein requirement. Ten elderly subjects aged 68-91 years (five men and five women) and ten young adult subjects aged 21-31 years (five men and five women) were infused with L-[1-13C]leucine for 9 h commencing in the postabsorptive state (0-3 h), continuing during the half-hourly feeding of low-protein meals (LP; protein 3% energy, 3-6 h), and during similar feeding of isoenergetic higher protein meals (HP; protein 15% energy, 6-9 h). Leucine oxidation and balance were determined from plasma [1-13C]-alpha-ketoisocaproate enrichment and expired 13CO2 excretion measured during the 3rd hour of each 3 h period. The protein intake during the HP phase was similar to the habitual intake estimated in the subjects from 24 h urinary N excretion. Metabolic demand was defined as equal to twice the body-protein equivalent of measured postabsorptive leucine oxidation. The efficiency of PPU was calculated from the increased leucine oxidation observed during feeding, and the apparent protein requirement was defined as metabolic demand/PPU and calculated in relation to both body weight (BW) and fat-free mass (FFM) determined by densitometry or bioimpedance. Metabolic demand in the young adults was 0.83 g protein/kg per d; in both elderly groups it was 36% lower when expressed per kg BW and 30% lower when expressed per kg FFM. The apparent protein requirement calculated from metabolic demand and PPU was 0.99 g protein/kg per d in the young adults and this was also lower in the elderly, although this was only significant in the men (0.66 g per kg BW, P = 0.013; 0.79 g per kg FFM, P = 0.02). The results show that in this group of healthy elderly adults protein requirements as assessed from leucine balance studies were either similar to or less than those of younger adults.

The purpose of this study was to identify possible relationships between the sum of knee flexion and extension peak torques and the severity of lower-body injuries in professional dancers. Twenty male [age 26.6 (± 6.0) years] and 22 female [age 27.1 (± 5.4) years] ballet and contemporary dancers reported one or more low-back, pelvis, leg, knee and foot injuries. The severity of injuries was established by recording the days off dance activities. Subjects were then monitored on a Cybex II or a KIN-CON isokinetic dynamometer. Knee flexion and extension peak torques were obtained bilaterally during three maximal contractions at the velocities of 1.04 and 4.19 rad/sec. No musculoskeletal injuries were reported at the time of data collection. At 1.04 rad/sec, results revealed significant correlation coefficients between relative thigh peak torques — expressed in Nm/kg fat free mass (FFM) — and prevalence of low extremity injuries. These findings suggest that the lower the thigh-power output, the greater the degree of injury. Female dancers demonstrated higher correlation coefficients (r -0.70; p < 0.005) than their male counterparts (r = -0.61; p < 0.01). However, no such correlations were found at the angular velocity of 4.19 rad/sec (p > 0.05), nor when low-back injuries and thigh-power outputs were considered at both velocities (p > 0.05). The main conclusions are: a) low thigh power outputs are likely to be associated with the severity of low extremity injuries, but not with low-back injuries, and b) such relationships are better identified at lower compared to higher isokinetic velocities.

Ten adult men were infused with L-[1-13C]leucine for 9 h commencing in the postabsorptive state (PA, 0-3 h), during the half-hourly feeding of low-protein meals (LP, protein = 2% calories, 3-6 h), and during feeding isoenergetic high-protein meals (HP, protein = 14% calories, 6-9 h). Leucine oxidation and turnover (protein synthesis and degradation) were determined from plasma alpha-[1-13C]ketoisocaproate enrichment and expired 13CO2 excretion measured during the third hour of each 3-h period. Plasma insulin increased markedly with feeding to a level that was maintained with both diets. The negative postabsorptive leucine balance became less negative during the LP meals (P < 0.01) and was positive with the HP meals (P < 0.01). The significant responses to feeding (all P < 0.01) were for oxidation -13% (PA-LP), +50% (LP-HP), and +29% (PA-HP); for degradation -24% (PA-LP), -30% (LP-HP), and -47% (PA-HP); and for synthesis -14% (PA-LP), +29% (LP-HP), and +11% (PA-HP). These data support a feeding mechanism involving both an insulin-mediated, protein-conserving influence of dietary energy that inhibits degradation, lowers amino acid levels, and reduces oxidation, and amino acid-mediated augmentation of the inhibition of degradation, a stimulation of synthesis, and an increase in oxidation when leucine dietary supply exceeds the capacity for its net deposition.

Conference Article| May 01 1996 Lipoproteins in non-insulin dependent diabetes mellitus (NIDDM) C.G.L. HOBBS; C.G.L. HOBBS 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar M. KODIKARA; M. KODIKARA 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar R. GRAY; R. GRAY 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar P. BORDIN; P. BORDIN 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar A. ROBINSON; A. ROBINSON 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar P.J. PACY; P.J. PACY 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar S. VENKATESAN; S. VENKATESAN 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar D. HALLIDAY D. HALLIDAY 1MRC Human Metabolism Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 1PG Search for other works by this author on: This Site PubMed Google Scholar Author and article information Publisher: Portland Press Ltd Online ISSN: 1470-8752 Print ISSN: 0300-5127 © 1996 Biochemical Society1996 Biochem Soc Trans (1996) 24 (2): 153S. https://doi.org/10.1042/bst024153s Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Cite Icon Cite Get Permissions Citation C.G.L. HOBBS, M. KODIKARA, R. GRAY, P. BORDIN, A. ROBINSON, P.J. PACY, S. VENKATESAN, D. HALLIDAY; Lipoproteins in non-insulin dependent diabetes mellitus (NIDDM). Biochem Soc Trans 1 May 1996; 24 (2): 153S. doi: https://doi.org/10.1042/bst024153s Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1996 Biochemical Society1996 Article PDF first page preview Close Modal You do not currently have access to this content.

Current post-prandial studies of amino acid metabolism and utilization are consistent with a feeding mechanism mediated primarily by insulin and amino acids, with the balance between protein conservation and net deposition dependent on the amino acid supply [1-13C]leucine post-prandial kinetic tracer studies of leucine oxidation, non-oxidative disappearance and endogenous appearance allow study of the regulation of whole-body amino acid oxidation, protein synthesis and proteolysis. On the basis of these studies it appears that for leucine oxidation, the main determinant of the efficiency of protein utilization, the overriding regulatory influence is substrate availability rather than insulin. Such substrate sensitivity is manifest throughout the physiological range of insulin down to the lowest insulin levels observed suggesting that a basal insulin need is not an important part of regulation of this important catabolic pathway. The key protein turnover response is an inhibition of proteolysis sufficient to limit any increases in amino acid levels thus limiting any increase in amino acid oxidation. It appears that the influences of amino acids and insulin on proteolysis are separate and additive and may both be receptor mediated so that extracellular amino acid levels can regulate intracellular levels. It is likely that protein synthesis is regulated by intracellular amino acid levels but post-prandial stimulation through increases in amino acid levels appears to be unhelpful because of parallel increases in amino acid oxidation. Evidence for any influence of insulin on protein synthesis has yet to be unequivocally identified.

Conference Article| May 01 1996 Apolipoprotein CII & CIII in Non-Insulin Dependant Diabetic Patients M. KODIKARA; M. KODIKARA 1Human Metabolic Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 Search for other works by this author on: This Site PubMed Google Scholar CGL. HOBBS; CGL. HOBBS 1Human Metabolic Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 Search for other works by this author on: This Site PubMed Google Scholar P. BORDIN; P. BORDIN 1Human Metabolic Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 Search for other works by this author on: This Site PubMed Google Scholar PJ. PACY; PJ. PACY 1Human Metabolic Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 Search for other works by this author on: This Site PubMed Google Scholar S. VENKATASAN; S. VENKATASAN 1Human Metabolic Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 Search for other works by this author on: This Site PubMed Google Scholar D. HALLIDAY D. HALLIDAY 1Human Metabolic Research Group, Unit of Metabolic Medicine, St. Mary's Hospital Medical School, Paddington, London W2 Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1996) 24 (2): 172S. https://doi.org/10.1042/bst024172s Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation M. KODIKARA, CGL. HOBBS, P. BORDIN, PJ. PACY, S. VENKATASAN, D. HALLIDAY; Apolipoprotein CII & CIII in Non-Insulin Dependant Diabetic Patients. Biochem Soc Trans 1 May 1996; 24 (2): 172S. doi: https://doi.org/10.1042/bst024172s Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1996 Biochemical Society1996 Article PDF first page preview Close Modal You do not currently have access to this content.

This study was designed to establish whether moderate aerobic exercise (2 h at 30-35% VO2 max) in lean non-athletic male adults had a prolonged stimulatory effect on energy expenditure while at rest. Four weight maintaining male adults had their 24 h energy expenditure measured by direct calorimetry on four separate occasions. During the 24 h in the calorimeter each subject received a diet which in total supplied 35 kcal (146 kJ) per kg body weight. All studies in an individual were completed within four to six weeks during which time body weight remained stable. On two of these 24 h periods, individuals rested throughout while on the other two, they also performed the prescribed exercise. This consisted of cycling for two 1 h sessions; the first while they were fasting while the second period was approximately 45 min after consuming a 800 kcal (3.4 MJ) meal. Total 24 h energy expenditure was greater on exercise (8.3 +/- 1.8 MJ/day) than non-exercising days (6.3 +/- 1.4 MJ/day, P < 0.001) In contrast when the acute effects of the cycling where removed 24 h resting energy expenditure on the exercise day (6.8 +/- 1.7 MJ/day) was not significantly different from that of rest days (95% confidence intervals of the difference ranged from -0.36 to 1.27 MJ/day). This study did not demonstrate a prolonged stimulatory influence on non-exercising resting energy expenditure following physical activity likely to be achieved by non-athletes. These data provide no evidence that such exercise is associated with a greater energy deficit than that due to the activity itself.

Conference Abstract| February 01 1995 Protein Balance in the Elderly: Comparison with Young Adults N Gibson; N Gibson 1Nutrition Research Unit, 4 St Pancras Way, London NW1 2PE Search for other works by this author on: This Site PubMed Google Scholar A Fereday; A Fereday 1School of Biological Sciences, Surrey University, GU2 5XH Search for other works by this author on: This Site PubMed Google Scholar M Cox; M Cox 1Nutrition Research Unit, 4 St Pancras Way, London NW1 2PE Search for other works by this author on: This Site PubMed Google Scholar J Millward; J Millward 1School of Biological Sciences, Surrey University, GU2 5XH Search for other works by this author on: This Site PubMed Google Scholar P Pacy P Pacy 1Nutrition Research Unit, 4 St Pancras Way, London NW1 2PE Search for other works by this author on: This Site PubMed Google Scholar Clin Sci (Lond) (1995) 88 (s32): 10P–11P. https://doi.org/10.1042/cs088010Pc Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation N Gibson, A Fereday, M Cox, J Millward, P Pacy; Protein Balance in the Elderly: Comparison with Young Adults. Clin Sci (Lond) 1 February 1995; 88 (s32): 10P–11P. doi: https://doi.org/10.1042/cs088010Pc Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsClinical Science Search Advanced Search This content is only available as a PDF. © 1995 The Biochemical Society and the Medical Research Society1995 Article PDF first page preview Close Modal You do not currently have access to this content.