5. Altered metabolic rate

Sukhatme and Margen specify that there is "no absolute energy requirement for any day or period". This is self-evident if one chooses not to specify the degree of physical activity and food intake, but simply assesses free-living people undertaking a variable pattern of activity and eating. The authors' sentence seems to be more subtle, however, implying that people can change their metabolic efficiency so that, while engaging in similar activity and eating, they adjust their total energy expenditure. It is this concept which is tackled by Beaton and Viteri, because Sukhatme and Margen clearly prefer regulation of expenditure rather than intake as the mechanism for autocorrelations in energy imbalances (see p. 361, column 2): "it seems more likely that the body regulates its energy balance by varying the efficiency of energy utilization". They then proceed to propose that from their own studies on RMR and the thermic effects of meals the "cost of maintenance cannot be constant as assumed in the literature but that it is regulated".