Mechanisms and nutritional significance of metabolic responses to altered intakes of protein and amino acids, with reference to nutritional adaptation in humans

Article Abstract:

Research has shown that the human body adapts to varying levels of protein intake within a reasonable range by increasing or decreasing the rate of protein metabolism. Important metabolic processes, such as the utilization of amino acids (building blocks of proteins), protein breakdown, and protein synthesis can be maintained at reduced rates when dietary protein is curtailed. The ways in which the body adapts at the cellular level to low protein intake are discussed. The availability of certain key amino acids influences protein synthesis, because amino acids are required in set proportions to manufacture a given protein. The concept of nutritional adaptation is discussed in reference to protein intake; adaptation can be defined as the process that allows the individual to adjust to a change in diet without suffering negative consequences. Successful adaptation often requires alterations in one or more body processes and is, therefore, not without costs; perhaps one critical function is preserved while another less important function is diminished. Accommodation is a related but distinct process in which the adjustment made has clear adverse effects. These concepts are illustrated with examples of amino acid flux and protein turnover. The authors conclude that current internationally accepted protein requirements are too low; intake at this level necessitates accommodation. Many populations habitually consume substantially more protein than the accepted requirement. If these persons were to reduce protein intake to the requirement, their bodies would not maintain an adapted, or desirable, nutritional state and would be vulnerable to major physiological stresses. (Consumer Summary produced by Reliance Medical Information, Inc.)

Standards, Research, Nutritional aspects, Protein metabolism, Amino acid metabolism, Proteins in human nutrition, Dietary protein

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Nutritional adaptation in man: general introduction and concepts

Article Abstract:

Nutrition scientists have established that individuals differ from each other in their needs for nutrients; all people do not share one optimal level of nutrient intake. Instead there is a range of intakes that will support human health. Circumstances including illness and physiological states such as pregnancy also affect the need for various nutrients. Individuals show an ability to adapt when nutrition is inadequate and the amount of nutrients consumed falls outside the appropriate range. For example, when calorie intake is curtailed as in starvation, the metabolic rate slows down so that less energy is used for basic body functions. The process of human nutritional adaptation is explored through a discussion of relevant concepts. At the most basic level, adaptation refers to the ability of the human species to survive in its environment. Over the course of history, man has adapted physically to the available sources of nutrition. A state of adaptation is by definition sustainable, meaning adaptation is not temporary but can be successfully maintained over time. Adaptations are always made at some cost and involve a choice, whether conscious or not. Nutritional adaptation may serve a purpose, but this does not mean that it is wholely beneficial; another function may be sacrificed in order to make the adaptation. (Consumer Summary produced by Reliance Medical Information, Inc.)

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1989 AIN/ASCN symposium - nutritional adaptation: concepts, mechanisms, and health significance: introduction to the symposium on nutritional adaptation

Article Abstract:

Nutrition scientists have established that for every nutrient, there is a range of intakes that will support health over the long-term; the needs of individuals vary and there is no one optimal level of intake applicable to all persons. Yet the boundaries of these ranges are controversial. Extremely low or high intakes of a nutrient are detrimental, but the point at which adverse consequences begin is often unclear. A symposium on nutritional adaptation was held at the March 1989 meeting of the Federation of American Societies of Experimental Biology, held in New Orleans. Scientists discussed the range of adequate nutrient intake in various circumstances, such as illness or environmental stresses. The way in which the human body adapts to nutrient intakes that are outside the appropriate range, and the circumstances in which the adaptation mechanisms fail, were reviewed. A particularly important topic in this area was adaptation to inadequate protein and energy intake, since starvation continues to exist worldwide. The consequences of protein and energy malnutrition, including reduced physical activity and social interactions, were emphasized. (Consumer Summary produced by Reliance Medical Information, Inc.)

Complications and side effects, Malnutrition

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