How can we assess "thrifty" and "spendthrift" phenotypes?

Abstract

Purpose of review: There is a large inter-individual variability in the magnitude of body weight change that cannot be fully explained by differences in daily energy intake and physical activity levels and that can be attributed to differences in energy metabolism. Measuring the short-term metabolic response to acute changes in energy intake can better uncover this inter-individual variability and quantify the degree of metabolic thriftiness that characterizes an individual's susceptibility to weight gain and resistance to weight loss. This review summarizes the methods used to identify the individual-specific metabolic phenotype (thrifty vs. spendthrift) in research and clinical settings.

Recent findings: The metabolic responses to short-term fasting, protein-imbalanced overfeeding, and mild cold exposure constitute quantitative factors that characterize metabolic thriftiness.

Summary: The energy expenditure response to prolonged fasting is considered the most accurate and reproducible measure of metabolic thriftiness, likely because the largest energy deficit best captures interindividual differences in the extent of metabolic slowing. However, all the other dietary/environmental challenges can be used to quantify the degree of thriftiness using whole-room indirect calorimetry. Efforts are underway to identify alternative methods to assess metabolic phenotypes in clinical and outpatient settings such as the hormonal response to low-protein meals.

Figure 1 –. Example of a minute-by-minute EE time course in a whole-room calorimeter and breakdown of the 24hEE components.

(A) Time course of EE measured minute by minute EE during a 24-h stay in a whole-room calorimeter. Meals are delivered to the participant inside the calorimeter through a small airlock at the indicated times. (B) Components of 24hEE: sleeping metabolic rate, awake metabolic rate, diet-induced thermogenesis, and physical activity EE. 24hEE, 24h energy expenditure; EE, energy expenditure.

Figure 2 –. Current methods to assess metabolic thriftiness.

24hEE, 24h energy expenditure; RMR, resting metabolic rate.