Adaptation to Low Protein and Energy Intakes

This paper focuses on two principal issues. First, what are the consequences of low dietary protein and amino acid intakes? Second, what are the physiological and social limits to restricted energy intakes? The concepts of adaptation and accommodation are presented. It is suggested that the limit of adaptation to low dietary protein is achieved at the intake level considered minimally necessary to maintain health in well-nourished subjects, as judged by nitrogen balance, stable lean body mass and absence of functional impairment. For lower protein intakes survival is prolonged via an accommodation, involving loss of lean body mass and reduced rates of protein and amino acid turnover. There is only a limited metabolic capacity for adaptation to reduced energy intakes, but variations in the level and pattern of physical activity permit a maintenance of body energy balance over a broad range of energy intakes. Where reduced physical activity to balance restricted energy intakes has adverse social, cultural and/or economic consequences the response should be viewed as an accommodation and not as adaptation. The range of adaptation depends on the criteria of normality and the assessment of the biological and social costs of changes with low intakes.