To present recent evidence on organ and tissue metabolic rates in humans to explain the variance in resting energy expenditure (REE).
In humans, present knowledge on specific metabolic activities (i.e. ki-values) refers to seven organs and tissues – brain, heart, liver, kidneys, skeletal muscle, adipose tissue and residual mass – with ki-values of 240, 440, 200, 440, 13, 4.5 and 12 kcal/kg/day, provided by Elia in 1992. Detailed body composition data, as derived from whole body MRI together with measurements of whole body REE, were used to validate ki-values in nonobese, healthy and middle-aged adults. There is no sex difference, but minor, that is 2 and 3% deviations are found for age above 55 years and obesity, respectively. By contrast, in adolescents, differences of about 100 kcal/day or 7.3% of measured REE were observed. There is first evidence for changes in ki-values with either weight loss or weight regain after weight loss. Altogether these data suggest that in adolescence and at age above 55 years, in the obese and with weight change, organ and tissue masses differ in cellularity and/or their specific metabolic rates. Presently, direct assessment of specific organ and tissue metabolic rates in humans by either NMR spectroscopy or PET, together with detailed body composition analysis, has not been performed systematically.
We need to become more skilled in methods and models used for detailed body composition analysis together with detailed assessment of energy expenditure in humans.
aInstitut für Humanernährung und Lebensmittelkunde, Christian-Albrechts-Universität zu Kiel, Germany
bObesity Research Center, St. Luke's Roosevelt Hospital, Columbia University College of Physicians and Surgeons, New York City, New York
cPennington Biomedical Research Center, Baton Rouge, Louisiana, USA
dUniversität Hohenheim, Institut für Ernährungsmedizin, Angewandte Ernährungswissenschaft/Diätetik, Stuttgart, Germany
Correspondence to Professor Dr Manfred James Müller, Institut für Humanernährung und Lebensmittelkunde, Christian-Albrechts-Universität zu Kiel, Düsternbrooker Weg 17, D-24105 Kiel, Germany. Tel: +49 431 880 5670; fax: +49 431 880 5679; e-mail: email@example.com