The intake of non-essential amino acids is a quantitatively important part of total protein intake and the proportion of non-essential N in total dietary N can significantly affect animal performance. The contradictory data on the optimum ratio between essential and nonessential amino acids for growth and protein deposition published in the literature arise mostly from different ways of expressing their relationships and defining their essentiality. When expressing the relations between both amino acid groups as a ratio of essential N to total amino acid N (E:T), the estimates of optimum E:T values are similar both within and among species. Unlike the ideal essential amino acid pattern which is independent of dietary factors and the type of response measured, the optimum E:T ratio is not universally valid. At a constant concentration of total dietary N, approximately the same E:T ratio is required for maximum growth rate, protein deposition or total protein utilization. However, at a constant concentration of essential N allowing rapid growth, higher nonessential N intake and consequently lower E:T ratio is needed for maximum N retention than for optimum protein utilization. Nutritional strategies aimed at achieving maximum growth rate or minimum N excretion should take these facts into consideration.
Most experiments investigating the relationships between essential and non-essential amino acids have been conducted with growing animals. Very little is known about optimum E:T ratios for other physiological functions such as maintenance or reproduction or about the role of non-essential and semi-essential amino acids in processes not directly related to protein metabolism. There is indirect evidence suggesting that the relative requirement for non-essential N for maintenance is considerably higher than that for growth. However, experimentally based estimates of optimum E:T ratio for maintenance are not available. It seems also that some nonessential amino acids may have essential character under certain conditions including maintenance but their physiological role has not been fully elucidated. Nevertheless, there is increasing evidence that the assumption of mutual interconversion of non-essential amino acids as sources of non-specific N may not be entirely valid and that a certain amount of non-essential amino acids must be supplied preformed in the diet to achieve maximum utilization of dietary protein.
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Many women who have recently given birth are always interested in attempting to lose some of that extra weight that traditionally accompanies having a baby. What many of these women do not entirely realize is the fact that breast-feeding can not only help provide the baby with essential vitamins and nutrients, but can also help in the weight-loss process.