Net Nitrogen Balance Research Articles

Response of Starter Nitrogen and Phosphorus Fertilizer Rates to Nodulation, Nitrogen Fixation, and Net Nitrogen Balance on Groundnut (Arachis hypogaea L.) in the Semi-arid Tigray Region of Ethiopia

Response of Starter Nitrogen and Phosphorus Fertilizer Rates to Nodulation, Nitrogen Fixation, and Net Nitrogen Balance on Groundnut (Arachis hypogaea L.) in the Semi-arid Tigray Region of Ethiopia

Net energy, energy utilization, and nitrogen and energy balance affected by dietary pea supplementation in broilers.

Pea starch consists predominantly of C-type of amylopectin chain which is more resistant to digestive enzymes than A-type of starch thus slowly digested in poultry. It was hypothesized that the presence of slowly digested pea starch in broiler diets will increase net energy and the efficiency of energy utilization in broilers. Two experiments were performed to investigate starch digestibility of pea at different incubation times (in vitro study) and the effect of dietary pea on heat increment and net energy in broilers using an open-circuit respiratory calorimetry system (in vivo study). One-day-old Ross 308 male broilers were fed a common starter crumble from d 1 to 10 and standard grower diets thereafter. At d 21, birds were transferred to the chambers each housing 2 birds. Each treatment was replicated 6 times with 2 identical runs of 3 replicates per treatment. A wheat-soybean meal-based diet was used as a control and the treatment diet contained 500 g of pea/kg pea. In vitro study showed that pellet processing increased (P < 0.001) starch digestibility, particularly at shorter times for wheat and a much larger response for pea. Birds offered the pea-based diet had lower (P = 0.002) feed intake, lower (P = 0.020) body weight gain, but a similar (P > 0.05) FCR compared to those offered the wheat-based diet. Net energy (NE) and apparent metabolizable energy (AME) values were higher in the pea-based diet than in the wheat-based diet (P = 0.037 for NE and P = 0.018 for AME). Heat production, respiratory quotient, heat increment of feed, efficiency of utilization of gross energy for AME, and efficiency of utilization of AME for NE did not differ (P > 0.05) between the 2 treatments. There was no effect (P > 0.05) of pea on the total tract digestibilities of dry matter, crude protein and ash, but the total tract digestibility of starch was higher (P = 0.022) in the pea-based diet compared to the wheat-based diet. This study provides insight into the energy metabolism of broilers offered a pea-based diet and indicates that dietary pea supplementation increases dietary AME and NE but has no effect on heat increment of feed and the efficiency of energy utilization in broilers.

Pilot Study Examining the Influence of Potassium Bicarbonate Supplementation on Nitrogen Balance and Whole-Body Ammonia and Urea Turnover Following Short-Term Energy Restriction in Older Men.

With aging there is a chronic low-grade metabolic-acidosis that may exacerbate negative protein balance during weight loss. The objective of this randomized pilot study was to assess the impact of 90 mmol∙day−1 potassium bicarbonate (KHCO3) versus a placebo (PLA) on 24-h urinary net acid excretion (NAE), nitrogen balance (NBAL), and whole-body ammonia and urea turnover following short-term diet-induced weight loss. Sixteen (KHCO3; n = 8, PLA; n = 8) older (64 ± 4 years) overweight (BMI: 28.5 ± 2.1 kg∙day−1) men completed a 35-day controlled feeding study, with a 7-day weight-maintenance phase followed by a 28-day 30% energy-restriction phase. KHCO3 or PLA supplementation began during energy restriction. NAE, NBAL, and whole-body ammonia and urea turnover (15N-glycine) were measured at the end of the weight-maintenance and energy-restriction phases. Following energy restriction, NAE was −9.8 ± 27.8 mmol∙day−1 in KHCO3 and 43.9 ± 27.8 mmol∙day−1 in PLA (p < 0.05). No significant group or time differences were observed in NBAL or ammonia and urea turnover. Ammonia synthesis and breakdown tended (p = 0.09) to be higher in KHCO3 vs. PLA following energy restriction, and NAE was inversely associated (r = −0.522; p < 0.05) with urea synthesis in all subjects. This pilot study suggests some benefit may exist with KHCO3 supplementation following energy restriction as lower NAE indicated higher urea synthesis.

Bioturbating invertebrates enhance decomposition and nitrogen cycling in urban stormwater ponds

Stormwater retention ponds manage runoff in developed areas, reducing flooding and erosion, and improving downstream water quality. Urban ponds also serve as habitat for aquatic organisms in an otherwise terrestrial habitat. However, the relationship between common pond species and biogeochemical function of ponds is poorly understood. Using a microcosm experiment, we evaluated the influence of two bioturbating invertebrates, Chironomus sp. and Lumbriculus variegatus, on sediment–water column nutrient exchange and benthic metabolism in stormwater ponds with divergent management histories and sediment organic matter (OM) content. Both organisms facilitated net release of reactive inorganic nitrogen to the water column, flipping the net reactive nitrogen balance of sediments relative to controls. Release of ammonium to the water column and sediment oxygen consumption were enhanced by both species, especially during colonization, but sediment uptake of nitrate was strongly enhanced by Chironomus and inhibited by L. variegatus. Comparison with direct animal respiration and excretion rates allows attribution of direct relative to indirect effects of bioturbation and bioirrigation. The influence of L. variegatus is predominantly direct, whereas Chironomus has strong direct and indirect biogeochemical effects. After 30 days, microalgal photosynthetic efficiency was reduced in all L. variegatus treatments, and context specific interactions appeared, with a reduction in OM in sediment with initially higher values, and reduced nitrate uptake in sediments with lower OM. Animal impacts on key processes ultimately influence downstream water quality and this study illustrates the important role of tolerant benthic invertebrates in mediating ecosystem functions in even the most disturbed aquatic ecosystems.

Sex differences in amino acids lost via sweating could lead to differential susceptibilities to disturbances in nitrogen balance and collagen turnover

Fluid collected during sweating is enriched with amino acids derived from the skin’s natural moisturising factors and has been termed “faux” sweat. Little is known about sex differences in sweat amino acid composition or whether faux sweat amino acid losses affect nitrogen balance. Faux sweat collected by healthy adults (n = 47) after exercise, and at rest by chronic fatigue patients, was analysed for amino acid composition. Healthy females had higher total amino acid concentrations in sweat (10.5 ± 1.2 mM) compared with healthy males (6.9 ± 0.9 mM). Females had higher levels of 13 amino acids in sweat including serine, alanine and glycine. Higher hydroxyproline and proline levels suggested greater collagen turnover in females. Modelling indicated that with conservative levels of exercise, amino acid losses in females via faux sweat were triple than those predicted for urine, whereas in males they were double. It was concluded that females were more susceptible to key amino acid loss during exercise and/or hot conditions. Females reporting chronic fatigue had higher levels of methionine in faux sweat than healthy females. Males reporting chronic fatigue had higher levels of numerous amino acids in faux sweat compared to healthy males. Higher amino acid loss in faux sweat associated with chronic fatigue could contribute to a hypometabolic state. Depending on activity levels, climatic conditions and gender, amino acid losses in sweat and skin leachate could influence daily protein turnover where periods of continuously high turnover could lead to a negative net nitrogen balance.

Measurement and Modeling of N Balance Between Atmosphere and Biosphere over a Grazed Grassland (Bugacpuszta) in Hungary

This work is a synthesis of a 5-year estimation of nitrogen balance at a semi-arid, semi-natural, undisturbed grassland site (Bugac). We measured the N input of atmospheric pollutants by wet and dry deposition of gases and aerosols, while we considered N output as NO and N2O gases volatilized from soil. Besides measurements of soil fluxes, the denitrification-decomposition (DNDC) ecological model was also used and simulations were compared to and validated against the measured values. The daily flux simulations generally did not match well the measured data for N2O and NO. In most cases, the mean fluxes were underestimated, though results of the comparison of monthly values suggest that model data, together with observed deposition data, are applicable to estimate the net N balance for grasslands. The calculated yearly N balance (net flux) between atmosphere and surface, without biological fixation and effect of grazing, ranged between −9.4 and −14 kg N ha−1 year−1 as the sum of the measured deposition and emission terms, −11 to −15 and 0.9 to 2.9 kg N ha−1 year−1, respectively, between 2006 and 2010. Observed and modeled soil emissions were lower by one order of magnitude than atmospheric deposition. Considering the biological nitrogen fixation and the effect of grazing (effects of both grazed plant and excreta), the net nitrogen balance varies within −6.6 and −11 kg N ha−1 year−1. It seems — taking into account the high uncertainty in calculation due to the effect of grazing — that sources of nitrogen exceed the sinks; the surplus is probably mineralized in the soil.

Macronutrient Metabolism in Starvation and Stress.

In starvation and to a lesser extent in stress starvation, the loss of protein mass is spared as much as possible. This metabolic arrangement must have developed under the influence of evolutionary pressure in view of the importance of protein mass for function and longevity. Peripheral adipose tissue mass is only limiting when its mass is extremely small. Protein is the predominant precursor of glucose in (stress) starvation and glucose is an essential substrate for the synthesis and maintenance of cells and matrix and for the control of the redox state. To spare protein, glucose should be used efficiently only for those purposes that cannot be achieved by fat. It is suggested that this is achieved by limiting full glucose oxidation and increasing fatty acid and ketone body oxidation, which most likely can also largely cover energy needs of the central nervous system. In stress states, net negative nitrogen balance (catabolism) largely results from net losses of peripheral protein mass, predominantly muscles, whereas central organs (e.g. the liver), the immune system and wound healing are anabolic. A number of factors are responsible for a net negative nitrogen balance which may ultimately lead to death if stress persists. In stress, the amino acid mix derived from peripheral (predominantly muscle) tissues is modified in interplay with the liver and to a minor extent the kidney. This mix is different in nonstressed conditions, containing substantially increased amounts of the nonessential amino acids glutamine, alanine, glycine and (hydroxy)proline. Part of the amino acid skeletons released by muscles are substrates to produce glucose in the liver and kidney. Glucose and the amino acids produced especially serve as substrates for cell proliferation and matrix deposition. The catabolic processes in peripheral tissues cannot be countered completely by adequate nutritional support as long as stress persists. This metabolic arrangement dictates a nutritional mix containing liberal amounts of protein and carbohydrates and addition of lipids to cover energy requirements.

Prediction of Yield and Nitrogen Uptake of Wheat from Net Nitrogen Balance after Rice in Rice–Wheat Cropping System

Net nitrogen (N) balance after rice (Oryza sativa L.) and its relationship with yield and N uptake of succeeding wheat crop was studied in a greenhouse. Three urea-enriched green manures, namely dhaincha (Sesbania aculeata L.), cowpea (Vigna unguiculata L.), and guar (Cyamopsis tetragonoloba L.) were compared with split application of urea in a rice–wheat cropping sequence. After rice, a negative N balance was measured in all treatments; however, the N balance values were greater with urea than with green manures. The N balance was positively correlated with the N content but negatively correlated with lignin content and carbon (C)–N ratio of the green manures. Lignin content was a better index than C/N ratio for predicting the net N balance, which described 82.3% of the total variations. Efficiency of residual N utilization by wheat could be determined by estimating the N balance after rice. Net N balance after rice can be used as a yardstick for the prediction of yield and N uptake by wheat crop.

Nutritional value of the marine algae wakame (Undaria pinnatifida) and nori (Porphyra purpurea) as food supplements

The nutritional properties of seaweeds are incompletely known, and studies on nutrient bioavailability are scarce, although such information is required to evaluate seaweed as a foodstuff. In the present study, samples of wakame (Undaria pinnatifida) and nori (Porphyra purpurea) were analysed to determine their chemical composition. To evaluate the algae as dietary supplements, the effects on rats of the inclusion of these seaweeds in a standard rodent diet were investigated. The control rats were fed a diet containing 100 % standard rodent diet. The wakame diet was obtained by mixing 10 % dried wakame with 90 % standard rodent diet, and the nori diet was obtained by mixing 10 % dried nori with 80 % standard rodent diet and 10 % starch. Food intake and the body weight were measured. Nitrogen ingested and excreted were determined to calculate true digestibility, biological value, net protein utilization and nitrogen balance. Biochemical determinations were made on serum blood samples. The protein content was high (16.8 % for wakame and 33.2 % for nori), the fat content was low (1 % for wakame and 2.8 % for nori) and the carbohydrates comprised 37 % for both seaweeds. The fibre and ash contents in wakame were 16.9 and 28.3 %, respectively, and in nori, they were 7.5 and 21.3 %, respectively. Both seaweeds contain high concentrations of calcium, sodium, potassium, iron and magnesium, and the most abundant vitamin was vitamin A. Few changes were observed in the nutritional parameters, but LDL cholesterol levels were significantly lower in rats fed with seaweed-supplemented diets than in the control rats. Wakame and nori are excellent sources of nutrients and are well accepted by experimental animals.

Leucine-protein supplemented recovery feeding enhances subsequent cycling performance in well-trained men

The purpose of this study was to determine whether a practical leucine-protein, high-carbohydrate postexercise feeding regimen could improve recovery, as measured by subsequent cycling performance and mechanistic markers, relative to control feeding. In a crossover, 10 male cyclists performed 2- to 2.5-h interval training bouts on 3 consecutive evenings, ingesting either leucine-protein, high-carbohydrate nutrition (0.1/0.4/1.2/0.2g·kg(-1)·h(-1); leucine, protein, carbohydrate, fat, respectively) or isocaloric control (0.06/1.6/0.2g·kg(-1)·h(-1); protein, carbohydrate, fat, respectively) nutrition for 1.5h postexercise. Throughout the experimental period diet was controlled, energy and macronutrient intake balanced, and protein intake clamped at 1.6g·kg(-1)·day(-1). The alternate supplement was provided the next morning, thereby isolating the postexercise nutrition effect. Following 39h of recovery, cyclists performed a repeat-sprint performance test. Postexercise leucine-protein ingestion improved mean sprint power by 2.5% (99% confidence limit,±2.6%; p = 0.013) and reduced perceived overall tiredness during the sprints by 13% (90% confidence limit,±9.2%), but perceptions of leg tiredness and soreness were unaffected. Before exercise, creatine-kinase concentration was lowered by 19% (90% confidence limits,±18%), but lactate dehydrogenase and pressure-pain threshold were unaltered. There was a small reduction in anger (25%± 18%), but other moods were unchanged. Plasma leucine (3-fold) and essential amino acid (47%) concentrations were elevated postexercise. Net nitrogen balance trended mildly negative in both conditions (mean± SD: leucine-protein,-20± 46mg·kg(-1) per 24h; control, -25± 36mg·kg(-1) per 24h). The ingestion of a leucine-protein supplement along with other high-carbohydrate food following intense training on consecutive days enhances subsequent high-intensity endurance performance and may attenuate muscle membrane disruption in well-trained male cyclists.

Effect of High-Protein Feeding on Performance and Nitrogen Balance in Female Cyclists

The effect of dietary protein ingested after exercise on recovery in women athletes is unknown. Therefore, we asked whether there is a meaningful difference between high- and low-protein recovery diets on the subsequent performance of well-trained female cyclists. In a crossover, 12 female cyclists completed three high-intensity rides composed of 2.5-h intervals on day 1, followed by repeat-sprint performance tests on days 2 and 4, interspersed with a rest day. During the 4-h recovery on days 1 and 2, cyclists ingested 1.4/0.7/0.26 or 2.1/0.1/0.26 g·kg(-1)·h(-1) of CHO/protein/fat in high-protein or isocaloric control conditions, respectively. At other times, cyclists ingested an isoenergetic high-CHO diet. No effect of protein dose on the mean power during repeat sprint was evident on day 2 (high-protein vs control = -1.1%; 95% confidence limits = ±4.6%) or on day 4 (1.7%; ±4.6%); furthermore, fatigue effects (slope) were unclear (day 2 = 1.4%; ±4.9%, day 4 = 0.5%; ±4.9%). Perceptions of leg tiredness and soreness were increased, and leg strength was reduced in the high-protein condition relative to control. In the high-protein condition, plasma glucose concentrations were lower during recovery, and plasma lactate concentrations were lower during the sprints. Effects on circulating creatine kinase activity were trivial. Net nitrogen balance during the experiment was positive in the high-protein condition (mean ± SD = 177 ± 140 mg of N·kg(-1) fat-free mass) but negative in the control condition (-81 ± 73 mg of N·kg(-1) fat-free mass); the estimated protein requirement was 1.28 g·kg(-1)·d(-1) (±0.57 g·kg(-1)·d(-1)). In contrast with the previous findings in males, we observed no clear influence of dietary protein quantity on the subsequent performance in females. The findings on nitrogen balance suggest that female cyclists training intensely have daily protein requirements approximately 1.6 times the recommended daily allowance but 0.65 times that of males

Nitrogen Depletion and Redistribution by Free‐Ranging Cattle in the Restoration Process of Mosaic Landscapes: The Role of Foraging Strategy and Habitat Proportion

In a mosaic landscape in N‐Belgium (W‐Europe), consisting of forest, grassland, and wooded pasture on former agricultural land, we assessed nitrogen redistribution by free‐ranging cattle (±0.2 animal units ha−1 yr−1). We examined if the spatial redistribution of nitrogen among habitats by cattle could restore nutrient‐poor conditions in preferred foraging habitats, and conversely whether such translocation could lead to extreme eutrophication in preferred resting habitats. We used nitrogen content of different diet classes, habitat use, foraging and defecation behavior, weight gain, and nitrogen losses in the actual situation to explore four different habitat proportion scenarios and two different foraging strategies to calculate a net nitrogen balance per habitat. An atmospheric deposition of 30 kg N ha−1 yr−1 with varying interception factors according to the habitat types was included in an integrated nitrogen balance. All scenarios showed a net nitrogen transport from grassland and wooded pasture to forest habitat. We found that nitrogen redistribution strongly depends on habitat proportion. Nitrogen losses from preferred grassland habitat can be high, given its proportion is small. Depletion is only to be expected at excretion‐free areas and probably is of minor importance to trigger the establishment of woody species. In general, nitrogen transported by cattle was much lower than input by atmospheric deposition, but grazing can compensate for high N inputs in excretion‐free areas and maintain grassland types that support critical loads of 20–25 kg N ha−1 yr−1. In none of the scenarios, N transport by cattle resulted in the exceeding of critical nitrogen loads to vulnerable forest ground vegetation.

A.S.P.E.N. Clinical Guidelines: Nutrition Support of the Critically Ill Child

careful selection of the appropriate mode of feeding and monitoring the success of the feeding strategy. The use of specific nutrients, which possess a drug-like effect on the immune or inflammatory state during critical illness, continues to be an exciting area of investigation. The lack of systematic research and clinical trials on various aspects of nutrition support in the PICU is striking and makes it challenging to compile evidence based practice guidelines. There is an urgent need to conduct well-designed, multicenter trials in this area of clinical practice. The extrapolation of data from adult critical care literature is not desirable and many of the interventions proposed in adults will have to undergo systematic examination and careful study in critically ill children prior to their application in this population. In the following sections, we will discuss some of the key aspects of nutrition support therapy in the PICU; examine the literature and provide best practice guidelines based on evidence from PICU patients, where available. While some PICU popu lations include neonates, A.S.P.E.N. Clinical Guidelines for neonates will be published as a separate series.

Functional impact of high protein intake on healthy elderly people

Decline in muscle mass, protein synthesis, and mitochondrial function occurs with age, and amino acids are reported to enhance both muscle protein synthesis and mitochondrial function. It is unclear whether increasing dietary protein intake corrects postabsorptive muscle changes in aging. We determined whether a 10-day diet of high [HP; 3.0 g protein x kg fat-free mass (FFM)(-1) x day(-1)] vs. usual protein intake (UP; 1.5 g protein x kg FFM(-1) x day(-1)) favorably affects mitochondrial function, protein metabolism, and nitrogen balance or adversely affects insulin sensitivity and glomerular filtration rate (GFR) in 10 healthy younger (24+/-1 yr) and 9 older (70+/-2 yr) participants in a randomized crossover study. Net daily nitrogen balance increased equally in young and older participants, but postabsorptive catabolic state also increased, as indicated by higher whole body protein turnover and leucine oxidation with no change in protein synthesis. Maximal muscle mitochondrial ATP production rate was lower in older people, with no change occurring in diet. GFR was lower in older people, and response to HP was significantly different between the two groups, with a significant increase occurring only in younger people, thus widening the differences in GFR between the young and older participants. In conclusion, a short-term high-protein diet increased net daily nitrogen balance but increased the postabsorptive use of protein as a fuel. HP did not enhance protein synthesis or muscle mitochondrial function in either young or older participants. Additionally, widening differences in GFR between young and older patients is a potential cause of concern in using HP diet in older people.

Effect of prolonged intravenous glucose and essential amino acid infusion on nitrogen balance, muscle protein degradation and ubiquitin-conjugating enzyme gene expression in calves

BackgroundIntravenous infusions of glucose and amino acids increase both nitrogen balance and muscle accretion. We hypothesised that co-infusion of glucose (to stimulate insulin) and essential amino acids (EAA) would act additively to improve nitrogen balance by decreasing muscle protein degradation in association with alterations in muscle expression of components of the ubiquitin-proteasome proteolytic pathway.MethodsWe examined the effect of a 5 day intravenous infusions of saline, glucose, EAA and glucose + EAA, on urinary nitrogen excretion and muscle protein degradation. We carried out the study in 6 restrained calves since ruminants offer the advantage that muscle protein degradation can be assessed by excretion of 3 methyl-histidine and multiple muscle biopsies can be taken from the same animal. On the final day of infusion blood samples were taken for hormone and metabolite measurement and muscle biopsies for expression of ubiquitin, the 14-kDa E2 ubiquitin conjugating enzyme, and proteasome sub-units C2 and C8.ResultsOn day 5 of glucose infusion, plasma glucose, insulin and IGF-1 concentrations were increased while urea nitrogen excretion and myofibrillar protein degradation was decreased. Co-infusion of glucose + EAA prevented the loss of urinary nitrogen observed with EAA infusions alone and enhanced the increase in plasma IGF-1 concentration but there was no synergistic effect of glucose + EAA on the decrease in myofibrillar protein degradation. Muscle mRNA expression of the ubiquitin conjugating enzyme, 14-kDa E2 and proteasome sub-unit C2 were significantly decreased, after glucose but not amino acid infusions, and there was no further response to the combined infusions of glucose + EAA.ConclusionProlonged glucose infusion decreases myofibrillar protein degradation, prevents the excretion of infused EAA, and acts additively with EAA to increase plasma IGF-1 and improve net nitrogen balance. There was no evidence of synergistic effects between glucose + EAA infusion on muscle protein degradation or expression of components of the ubiquitin-proteasome proteolytic pathway.

Apparent digestibilities of diets based on timothy and Italian ryegrass hay harvested in different regions in Japan fed to exercising Thoroughbreds

ABSTRACTThe apparent digestibility of diets based on timothy hay harvested in Hidaka in Hokkaido (HT) and Italian ryegrass hay harvested in Miyazaki in Kyushu (MI) were compared in Thoroughbreds undergoing exercise. The nitrogen retention and plasma‐free amino acid (AA) concentrations were also examined to evaluate the quality of the protein contained in the two types of hay. Four male Thoroughbreds (aged 34.4 ± 0.9 months (mean ± standard deviation) and weighing 506.3 ± 30.4 kg) undergoing exercise training at 80% of maximal heart rate were used for the study, and the apparent digestibility of the diets based on HT and MI was assessed. The net nitrogen balance was also measured by subtracting the amount of nitrogen excreted in the feces and urine from the total nitrogen intake. The apparent digestibilities of dry matter, energy, neutral detergent fiber and ether extract were all higher in the MI group than in the HT group (P &lt; 0.05). The larger energy digestibility in the MI group (56.8 ± 3.3%) compared with that in the HT group (51.6 ± 2.4%) was attributed to the relatively easy digestibility of hemicellulose. The net nitrogen balance and plasma AA concentrations did not differ significantly between the two forage groups. We concluded that the nutritive value of MI is adequate for exercising horses, even though the timothy and Italian ryegrass used in this study were second cuttings, and their nutrient values were not easily comparable.

Phosphate binder therapy for attainment of K/DOQI™ bone metabolism guidelines

Phosphate binder therapy for attainment of K/DOQI™ bone metabolism guidelines

Acid loading during treatment with sevelamer hydrochloride: Mechanisms and clinical implications

Short-term and long-term studies indicate that patients treated with sevelamer hydrochloride have lower serum bicarbonate levels than patients treated with calcium-containing phosphate binders. This observation has previously been attributed to withdrawal of a source of base with discontinuation of calcium carbonate or calcium acetate. However, understanding of the chemistry of sevelamer hydrochloride suggests at least three potential mechanisms whereby it might induce a dietary acid load. Moreover, preliminary results from an animal model demonstrate that treatment with sevelamer hydrochloride results in a fall in urine pH, as well as an increase in urinary ammonium and calcium excretion consistent with an increase in net acid excretion. Chronic metabolic acidosis in maintenance dialysis patients is associated with major systemic effects. It is independently associated with an increased risk of death in dialysis patients. Metabolic acidosis has both catabolic and antianabolic effects that may lead to a net negative nitrogen balance and total body protein balance. Metabolic acidosis also leads to physiochemical dissolution of bone and promotes cell-mediated bone resorption due to enhanced osteoclast activity and reduced osteoblast activity. It may also exacerbate secondary hyperparathyroidism and renal osteodystrophy. Given the long-term risks of chronic metabolic acidosis in maintenance dialysis patients, Kidney/Dialysis Outcome Quality Initiative (K/DOQI) guidelines have recently recommended maintaining predialysis serum levels of CO2 above 22 mmol/L in order to improve bone histology, and to ameliorate excess protein catabolism.

Introduction

Introduction

Dietary macronutrient recommendations for optimal Dietary macronutrient recommendations for optimal

A net positive nitrogen balance is needed for exerciseinduced muscle damage to be repaired during the recovery period. Apart from hormones and growth factors, adequate energy and amino acid availability contribute to this balance and influence the rate at which protein synthesis and muscle repair occur post-exercise. This paper reviews the dietary factors involved in muscle repair during the post-exercise recovery period. Both resistance and endurance-trained athletes have a higher dietary protein requirement of between 1.2 and 1.8 g protein/kg body weight (BW)/day, with an upper limit of 2 g protein/kg BW/day. To increase the rate of protein synthesis during the recovery period, immediate ingestion of protein postexercise is recommended. Additionally, ingesting 1.2 g carbohydrate (CHO)/kg BW/hour with 0.4 g/kg BW/hour of a wheat amino acid mixture (wheat protein hydrolysate combined with free leucine and phenylalanine) enhances the insulin response compared with ingesting CHO only or combined with other protein hydrolysates, peptides, or intact protein. This increased insulin response could increase muscle protein synthesis indirectly by altering the hormonal milieu. Results on the anabolic effect of single or mixtures of amino acids remains to be further elucidated. The possible antioxidant benefits of whey protein supplementation in athletes remains to be proven, while the antioxidant potential of soy protein holds promise. The effect of glutamine supplementation on protein synthesis in athletes is limited and its clinical relevance for enhanced immune function in endurance athletes remains to be established. Creatine supplementation seems to be beneficial in terms of protein synthesis and gains in fat free mass during the recovery period, while the use â-hydroxy â-methylbutyrate (HMB) supplementation by trained athletes seems to have limited benefits. It is important to keep dietary advice individualised considering the complexity in which the endocrine system regulates cell function, the diverse mechanisms that control homeostasis, as well as genetic variability. SA Sports Medicine Vol.16(2) 2004: 33-40