ESPE Yearbook of Paediatric Endocrinology

Science. 2021 Aug 13;373(6556):808–812 doi: 10.1126/science.abe5017

Brief summary: This study compiled a large database of doubly labeled water measurements on a large (N=6421) and diverse (N=29 countries) population aged between 8 days and 95 years to provide the first comprehensive study of total energy expenditure (TEE) and basal metabolic rate (BMR) over the human life span.

The results revealed that TEE increased with fat-free mass in a ‘power law’ manner with four distinct life phases: the first phase is neonates up to 1 year of age. Neonates had similar fat-free-, and fat mass-adjusted TEE and BMR as adults. Until 9–15 months of age, adjusted TEE and BMR both rise to values ~50% above respective adult values. In the second phase, ‘juveniles’ between 1 and 20 years of age, adjusted TEE and BMR steadily declined to meet adult levels. Interestingly, no puberty-related increase was evident among subjects aged 10–15 years. The third phase is adulthood from 20 years to 60 years with stable adjusted TEE and BMR, even for women during pregnancy. The fourth phase is adults aged >60 years, when adjusted TEE and BMR declined; subjects 90 years and older had levels ~26% below those of middle-aged adults.

The analyses provide empirical measures and predictive equations for TEE and BMR from infancy to senescence. The results shed light on metabolic changes across the life course, they identify critical periods for energy disbalance with respect to growth and development, and they challenge old beliefs: First, adolescents in puberty or women during pregnancy do not show a higher metabolic rate. Rather, it was infants and toddlers who burned the most calories when adjusted for body size, which may reflect elevated energy demands related to growth and development. Second, neonates revealed the same metabolic rate as their pregnant mothers, which is no different from other women when adjusted for body size. Third, the energy costs of physical activity and of tissue-specific metabolism were not constant throughout life but showed age-dependent differences. The findings highlight the importance of energy requirements during infancy for growth and development. By contrast, your ‘middle-age spread’ is not due to slowing of metabolism; rather this age-related decline was not apparent until after age 60 years, and so other lifestyle factors are to blame!