Advances in the understanding of specific metabolic rates of major organs and tissues in humans.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing physiological models and body composition data
PubMed 23924948 · doi:10.1097/MCO.0b013e328363bdf9
What was done
The authors reviewed evidence on human organ and tissue specific metabolic rates (ki-values) across seven organs and tissues (brain, heart, liver, kidneys, skeletal muscle, adipose tissue, and residual mass). They evaluated how well classical ki-values (Elia, 1992) combined with whole-body MRI body composition predict measured whole-body resting energy expenditure across sex, age, obesity, and weight change.
What was found
Classical ki-values are 240 kcal/kg/day for brain, 440 for heart, 200 for liver, 440 for kidneys, 13 for skeletal muscle, 4.5 for adipose tissue, and 12 for residual mass. In nonobese healthy middle-aged adults, there was no sex difference in prediction accuracy. Deviations were minor for adults older than 55 years (2%) and individuals with obesity (3%). In adolescents, deviations were approximately 100 kcal/day (7.3% of measured resting energy expenditure). Initial evidence was noted for changes in ki-values during weight loss or regain.
Why it matters
The review demonstrates that tissue-level metabolic rates are generally robust across sexes in healthy adults, but physiological shifts in organ cellularity or metabolic activity occur in adolescence, aging, obesity, and active weight change.
Limits
The abstract describes a narrative review without reporting search criteria, study counts, or participant sample sizes. Direct in vivo quantification of organ-specific metabolic rates via PET or NMR spectroscopy alongside comprehensive body composition analysis had not been systematically conducted.
Cited by
- supports Muscle tissue burns more calories at rest than fat tissue, meaning having more muscle increases resting metabolic rate.