Ellen Roitman

The Plasma Aminogram. I. Influence of the Level of Protein Intake and a Comparison of Whole Protein and Amino Acid Diets

Extract: The changes in plasma aminogram produced by variations in level of protein intake provided either as whole protein or a mixture of amino acids were studied. Controls were 29 normal infants, one to three months of age, fed a standard evaporated milk formula providing 3 to 3.5 g/kg/day of protein (fig. 1 and table II). Results obtained with the lowest protein intake (1.1 g/kg/day) are illustrated in figure 2 and presented in table III. Alterations in the plasma aminogram are noted as early as two days after the reduction in intake and become more pronounced as the feeding is prolonged. The most striking changes are depression of the branched chain amino acids (leucine, isoleucine and valine) and of lysine and tyrosine. Glycine and serine are elevated with glycine showing the greater elevation. Less striking changes are decreased concentrations of threonine, phenylalanine, ornithine, butyrine, cystine and proline.The aminograms obtained with feedings of 1.3 and 1.5 g/kg/day are very similar to those obtained with the more extreme degree of protein reduction (fig. 3 and table IV). The aminogram after feeding 1.7 g/kg/day remains within the range of average ±1 standard deviation except for the elevation of glycine.A high intake of milk protein, 9 g/kg/day, results in an increase in the levels of a majority of the amino acids (fig. 5 and table V). The sole exception is glycine, which tends to be low. Marked increases occur in the branched chain amino acids, valine being the most affected; there is also a large increase in the level of proline. The greatest elevations occur in the levels of methionine, which also show the most marked individual variation, elevations ranging from 2 to 35 times normal average value. An apparent tendency of the methionine level to return towards normal with prolonged feeding of the high protein diet is evident on the graph. The significance of this finding must be questioned, however, since the subjects who were maintained the longest on this diet were those who originally did not have the very high levels of methionine.There are some differences in the aminogram when infants are fed the equivalent of 3.5 g/kg/day in the form of amino acids instead of intact protein (fig. 6 and table VI). On the amino acid diets, lower average plasma values are seen for the branched chain amino acids, alanine, proline, asparagine and citrulline; higher values are observed for threonine and serine. The markedly elevated levels of plasma amino acid observed after feeding 9 g/kg/day of whole protein are not seen after feeding the equivalent amount of nitrogen as an amino acid mixture (fig. 7 and table VII). There is elevation only of valine and serine. When individual subjects were shifted from the high protein to the high amino acid diet, the pattern shifted within 24 hours.Speculation: A more precise and sensitive indicator of the state of protein nutrition is needed. While the level of the plasma amino acids changes rapidly with alterations in protein intake, much more work is necessary before it can be used to evaluate protein adequacy.

The Plasma Amino Acids in Malnutrition: Preliminary Observations

It is generally appreciated that malnutrition is the worlds foremost paediatric problem. Directly or indirectly it makes the major contribution to child mortality. Nevertheless, it remains an entity which is not well defined, or, more accurately, a combination of entities only some of which are well defined. We recognize the effects of certain specific food factors, the accessory food factors or vitamins, and we have some knowledge of changes brought about by deficits of the inorganic components of diet. The effects of caloric deficits, of protein deficits and of possible deficits of specific amino acids have, however, been difficult to separate. Protein and caloric deficits are commonly associated and the existence of syndromes of specific amino acid deficiency has not been definitely established although there is some evidence that they exist. It appears that the more exact definition of this area of deficiency will depend on chemical studies. We already know that plasma protein levels fall in protein deficiency, particularly the albumin fraction, and that blood urea is also reduced. We know that certain protein enzymes in the blood and the liver (Waterlow and Patrick, 1954; Burch, Arroyave, Schwartz, Padilla, Behar, Viteri and Scrimshaw, 1957) are diminished. It has seemed to us that observations on the free amino acids of the plasma might be of help in delineating specific entities within this area. The free amino acid level of the plasma might prove to be a more significant index of protein adequacy than other criteria that have been applied and the plasma free amino acid pattern, even if it could not be correlated with symptoms of specific amino acid deficiency, might yet be of considerable value in pointing to limiting amino acids and thus providing a sounder basis for dietary

The Essential Amino Acid Requirements of Infants IX. Isoleucine

Acurate knowledge of essential nutrients is a sine qua non of good nutrition. Such information is needed for the prevention and repair of dietary deficiencies arising from food shortages and also in situations where the capacity to handle food is limited by disease states. Evaluation of the requirements for essential amino acids has been peculiarly difficult, since this involves the construction of a diet in which the quantity of a single amino acid can be varied at will. The problem has been approached in several ways: 1. Use has been made of natural proteins deficient in one or another amino acid. This method has very limited applicability, for nature has been singularly unobliging in providing a variety of such proteins. 2. Chemically degraded proteins or protein hydrolysates have been used. A number of procedures can be used to destroy one or more amino acids, which can then be replaced in any quantity desired. Diets constructed from such preparations have the advantage that the amino acids are present for the most part as the natural isomers and that unessential as well as essential amino acids are present. There is, however, the disadvantage that the na