Whole-body protein kinetics in children with kwashiorkor and infection: a comparison of egg white and milk as dietary sources of protein

Uses of Stable Isotopes in the Assessment of Nutrient Status and Metabolism

Stable isotopes are nonradioactive and can be safely administered to humans; yet, because of the isotopic difference, can be distinguished from the unlabeled moiety and thus trace the nutrient uptake and elimination. Stable isotope applications include measurement of nutrient absorption, determination of nutrient body stores, tracing routes of nutrient metabolism, measuring nutrient fluxes through specific pathways, and measuring nutrient elimination. The ability to assess the dynamics of nutrient metabolism in vivo has been vital in the study of nutrient requirements, nutrient metabolism, mechanisms of nutrient homeostasis, and nutrient toxicity. Stable isotopes provide a window into human metabolism that is particularly valuable to the quantitative study of human nutrition.

Protein quantity, not protein quality, accelerates whole-body leucine kinetics and the acute-phase response during acute infection in marasmic Malawian children

The present study compared leucine kinetics and acute-phase-protein concentrations in three groups of marasmic, acutely infected Malawian children fed one of three isoenergetic diets. These were: an enhanced-protein-quality diet (egg-white+tryptophan, providing 1.2 g protein/kg per d; n 14); an increased-protein-content diet (egg-white+tryptophan, providing 1·8 g protein/kg per d; n 14); a standard-protein diet (1·2 g milk protein/kg per d; n 25). The hypotheses tested were that children receiving a diet with more protein would have greater rates of non-oxidative leucine disposal and that children receiving an isonitrogenous diet with a higher protein quality would have lower rates of leucine oxidation. The children were studied after 24 h of therapy using standard [13C]leucine stable-isotope tracer techniques. The children receiving the higher-protein-content diet had greater leucine kinetic rates than those receiving the standard-protein-content diet; non-oxidative leucine disposal was 170 (SD 52) v. 122 (SD 30) μmol leucine/kg per h (P<0·01). Leucine oxidation was less in the children receiving the enhanced-protein-quality diet than in those receiving the standard-protein-quality diet; 34 (SD 12) v. 45 (SD 13) μmol leucine/kg per h (P<0·05). The children receiving the high-protein-content diet increased their serum concentration for five of six acute-phase proteins 24 h after starting therapy, while those receiving the standard-protein-content diet did not. These data suggest that there was greater whole-body protein synthesis, and a more vigorous acute-phase response associated with the higher-protein-content diet. The clinical benefits associated with a higher protein intake in marasmic, acutely infected children need further study.

Effect of infections and environmental factors on growth and nutritional status in developing countries

Despite numerous advances and improvements in child health globally, malnutrition remains a major problem and underlies a significant proportion of child deaths. A large proportion of the hidden burden of malnutrition is represented by widespread single and multiple micronutrient deficiencies. A number of factors may influence micronutrient deficiencies in developing countries, including poor body stores at birth, dietary deficiencies and high intake of inhibitors of absorption such as phytates and increased losses from the body. Although the effects of poor intake and increased micronutrient demands are well described, the potential effects of acute and chronic infections on the body's micronutrient status are less well appreciated. Even more obscure is the potential effect of immunostimulation and intercurrent infections on the micronutrient distribution and homeostasis. The association therefore of relatively higher rates of micronutrient deficiencies with infectious diseases may be reflective of both increased predisposition to infections in deficient populations as well as a direct effect of the infection itself on micronutrient status indicators. Recently the association of increased micronutrient losses such as those of zinc and copper with acute diarrhea has been recognized and a net negative balance of zinc has been shown in zinc metabolic studies in children with persistent diarrhea. It is also recognized that children with shigellosis can lose a significant amount of vitamin A in the urine, thus further aggravating preexisting subclinical vitamin A deficiency. Given the epidemiological association between micronutrient deficiencies and diarrhea, supplementation strategies in endemic areas are logical. The growing body of evidence on the key role of zinc supplementation in accelerating recovery from diarrheal illnesses in developing countries supports its use in public health strategies.

Critical appraisal of the management of severe malnutrition: 3. Complications

The high case-fatality of severe malnutrition is due to infections, dehydration, electrolyte disturbances and heart failure. We focus on the evidence about managing these complications of severe malnutrition. Signs of circulatory collapse in severely malnourished children should be treated with intravenous or bone marrow infusion of Ringer's lactate with additional dextrose and potassium at a rate 20-40 mL/kg fast with close monitoring of vital signs. Recommendations for slow or restricted fluids in the face of shock are unsafe, and hypotonic or maintenance solutions must be avoided to prevent hyponatraemia. However, the evidence that severely malnourished children do not tolerate excessive fluid administration is good, so caution must be exercised with regards to fluids in the initial phase of treatment. There is also good evidence that wide spectrum antibiotics need to be given empirically for severe malnutrition to prevent the otherwise unavoidable early mortality. There is a need for improved protocols for tuberculosis diagnosis, HIV management and treatment of infants under 6 months with severe malnutrition. The contribution of environmental enteropathy to poor growth and nutrition during the weaning period means that there should be more priority on improving environmental health, particularly better hygiene and less overcrowding. A T-cell mediated enteropathy contributes to growth failure and malnutrition, and it is related to environmental contamination of enteric organisms in the weaning period rather than allergic responses.

Whole-body leucine kinetics and the acute phase response during acute infection in marasmic Malawian children

This study compared leucine kinetics and acute-phase protein and cytokine concentrations in three groups of Malawian children who were fed an isoenergetic, isonitrogenous diet: children with marasmus with (n = 25) and without (n = 17) infection and well-nourished children with infection (n =13). The hypotheses tested were that whole-body leucine kinetics will be less in marasmic acutely infected children than in well-nourished acutely infected children but greater than in marasmic uninfected children. Children were studied after 24 h of therapy using standard (13)C-leucine stable isotope tracer techniques. Well-nourished children with acute infection had greater leucine kinetic rates than did marasmic children with acute infection; nonoxidative leucine disposal was 153 +/- 31 versus 118 +/- 43 micromol leucine. kg(-1). h(-1), leucine derived from whole-body proteolysis was 196 +/- 34 versus 121 +/- 47, and leucine oxidation was 85 +/- 31 versus 45 +/- 13 (p < 0.01 for all comparisons). Leucine kinetic rates were similar in marasmic children with and without acute infection. Well-nourished children with acute infection increased their serum concentration of five of six acute-phase proteins during the first 24 h, whereas marasmic children with infection did not have any increases. The serum concentrations of IL-6 were elevated in well-nourished and marasmic children with infection. These data suggest that the cytokine stimulus for the acute-phase protein kinetic response to acute infection is present in marasmic children but that the acute-phase protein metabolic response is blunted by malnutrition.

Protein and amino acid requirements and the composition of complementary foods

In this paper, factorial models of the dietary requirements for protein, nitrogen and individual indispensable amino acids are developed from published information on the relationship between age and protein deposition and between protein (amino acid) intake and nitrogen balance. The results are used to develop recommendations on the protein-energy ratio and the amino acid pattern of the diet. As part of the development of the models, factors affecting dietary protein digestibility, bioavailability and efficiency of utilization are discussed. Over the age range of 6-24 mo the models predict a fall in the weight-specific protein and amino acid requirement that results almost entirely from the changes in the growth rate of the children. It is also concluded that the requirement for the maintenance of body protein equilibrium (so-called maintenance) changes little with age. This contrasts markedly with the relationship between age and energy requirements. The amino acid modeling implies that the optimum pattern of individual essential amino acids also changes only marginally across the age range considered in the report. The calculations of the dietary requirement for whole protein imply that achieving a minimum protein-energy ratio of 6.3% is desirable. The amount of protein needed from complementary foods for breast-fed children is discussed.

Colitis increases albumin synthesis at the expense of muscle protein synthesis in macronutrient-restricted piglets

Our aim was to examine the effect of acute inflammation localized in the colon and early macronutrient restriction on protein synthesis in a piglet model. In a 2 x 2 factorial design, piglets (n = 32) were fed an adequate or macronutrient-restricted diet with or without dextran sulfate-induced colitis for 7 d. The stable isotope tracer L-[5,5,5-(2)H(3)]leucine was infused to determine protein kinetics at the whole-body level and synthesis of tissue and plasma proteins. In the well-nourished state, colitis did not affect weight gain or protein kinetics except for an increase in albumin synthesis (P < 0.05). Macronutrient restriction alone caused a general slowing of protein metabolism including decreased weight gain (P < 0.0004), whole-body protein turnover (P < 0.0001), and liver (P < 0.01) and plasma protein (P < 0.03) synthesis. However, in the presence of macronutrient restriction, colitis compromised weight gain further (P < 0.02) and decreased muscle protein synthesis (P < 0.05) due to a redistribution of protein metabolism that supported enhanced synthesis of plasma proteins. The increased contribution of plasma protein synthesis to whole-body protein turnover was attributable mainly to increased synthesis of albumin (P < 0.006). Concentrations of plasma proteins were unaffected despite dramatic changes in their synthesis rates, thereby underestimating the effects of malnutrition and colitis on protein metabolism. Increased synthesis of plasma proteins, particularly the negative acute phase reactant albumin, compromises weight gain and muscle protein synthesis only when macronutrient intake is inadequate, underscoring the role of adequate nutrition in preventing growth impairment and muscle wasting in acute inflammation. These results suggest that the hypoalbuminemia of inflammatory bowel disease should not be attributed to decreased synthesis.

Protein intake and bone disorders in the elderly

Malnutrition, most notably protein deficiency, contributes to the occurrence of osteoporotic fractures not only by decreasing bone mass but also by altering muscle function. Furthermore, malnutrition is associated with increased morbidity in patients with osteoporotic fractures. The somatomedin system (IGF-1) may be directly involved in the pathogenesis of osteoporotic hip fractures and their complications in elderly patients. A low IGF-1 level is a risk factor for hip fracture. In subjects with appropriate intakes of vitamin D and calcium, giving protein supplements to correct an inadequate spontaneous protein intake increases circulating IGF-1 levels, improves clinical outcomes after hip fracture, and prevents bone mineral density loss at the proximal femur. Supplemental protein also significantly reduces the length of inpatient rehabilitation care. These data emphasize the importance of adequate nutrient intake in the prevention and treatment of osteoporotic fractures.

Plasma urea appearance rate is lower when children with kwashiorkor and infection are fed egg white-tryptophan rather than milk protein

In kwashiorkor, there is less endogenous proteolysis in response to acute infection than in a well-nourished state. Thus the amino acid composition of dietary protein may be more important in facilitating the acute phase response in kwashiorkor. This study tested the hypothesis that during the treatment of kwashiorkor with infection, there is a lower rate of urea appearance when the dietary intake of amino acids more closely resembles the amino acid composition of acute phase proteins. Thirty children in Malawi with kwashiorkor and acute infection were fed isoenergetic, isonitrogenous meals containing either egg white-tryptophan or milk as a protein source. After 24 h, the rates of urea appearance and whole-body protein breakdown and synthesis were measured with the use of 1-13C-leucine and 15N2-urea tracers. Plasma concentrations of seven acute phase proteins, interleukin 6 and tumor necrosis factor-alpha were measured on admission, and at 24 and 48 h. The 16 children who received egg white-tryptophan had lower rates of urea appearance than those who received milk [57+/-30 vs. 87+/-36 micromol/(kg x h), mean +/- SD, P<0.02]. No significant differences were found in the rates of whole-body protein turnover or in the concentration of any of the acute phase proteins or cytokines. The concentration of interleukin 6 was consistent with an appropriate proinflammatory response and correlated directly with the concentrations of C-reactive protein (r = 0.67, P<0.01) and alpha1-antitrypsin (r = 0.40, P<0.05). The findings suggest that egg white-tryptophan is associated with less amino acid oxidation in kwashiorkor and acute infection than is milk.

Severe hypophosphatemia in children with kwashiorkor is associated with increased mortality

Severe hypophosphatemia, serum phosphate concentration <0.32 mmol/L (<1.0 mg/dL), occurred in 8 of 68 (12%) of children with kwashiorkor within 48 hours of admission; 5 of 8 (63%) of these children died, compared with 13 of 60 (22%) children without severe hypophosphatemia (P <.02). Dermatosis and dehydration were significantly correlated with severe hypophosphatemia, but these clinical signs could not reliably predict fatal cases. Severe hypophosphatemia seems to be common and life-threatening in children with kwashiorkor in Malawi.

Lipopolysaccharide-induced reductions in food intake do not decrease the efficiency of lysine and threonine utilization for protein accretion in chickens

Exposure of animals to infectious agents induces immune responses that result in reductions in food consumption and weight gain. The effect of these changes on amino acid requirements and utilization remains unclear. Three assays were conducted with young chicks with Escherichia coli lipopolysaccharide (LPS) used to stimulate the immune system. An initial study was conducted to evaluate the effects of LPS on animal performance. In a daily or alternate day injection regimen for 9 d, chicks were given intraperitoneal injections of sterile saline containing 0, 100 or 400 microgram LPS. Administration of 100 or 400 microgram LPS daily, or every other day, decreased both weight gain and food consumption. In two subsequent growth assays, chicks were fed graded levels of lysine or threonine and injected with either 0 or 400 microgram LPS every other day to evaluate the effect of LPS administration on the efficiency of amino acid utilization. At the three lowest amino acid doses, whole-body protein accretion was a linear function of supplemental lysine or threonine intake, and slopes of the accretion curves were not altered by LPS administration. The dietary lysine concentration required to maximize protein accretion was unaffected by LPS, but the absolute lysine intake required to maximize chick performance was lower in LPS-injected chicks than in saline-injected chicks. These results show that LPS administration reduces weight gain, food intake, efficiency of food utilization and the absolute quantity of lysine required to maximize these criteria. However, LPS administration does not affect the efficiency of amino acid utilization, nor does it affect the concentration of dietary lysine required to maximize performance.