Energy metabolism in African Americans: potential risk factors for obesity.
BACKGROUND
Recent reports have identified a lower resting metabolic rate in African Americans than in whites, but most studies included only females and used short-term measurements with ventilated-hood systems.


OBJECTIVE
Our objective was to compare 24-h measurements of energy metabolism between African American and white women and men using a respiratory chamber.


METHODS
Thirty-eight African American (x +/- SD: 32 +/- 7 y of age, 24 +/- 10% body fat) and 288 white (31 +/- 7 y of age, 26 +/- 12% body fat) subjects spent 24 h in a respiratory chamber for measurement of 24-h energy expenditure (24EE), sleeping metabolic rate (SMR), 24-h respiratory quotient (24RQ), and substrate oxidation rates.


RESULTS
After adjustment for sex, age, and body composition (by hydrodensitometry), African Americans had lower SMR (-301 +/- 105 kJ/d; P < 0.01) and higher 24RQ (0.014 +/- 0.004; P < 0.001) than whites, whereas 24EE was similar. A sex-specific analysis, using a subset of 38 whites with an equal sex distribution and similar age and body weight, revealed that African American women had lower SMR (-442 +/- 182 kJ/d; P < 0.05) and lower 24EE (-580 +/- 232 kJ/d; P < 0.05), but similar 24RQ values compared with white women. African American men tended to have lower SMRs than white men (-355 +/- 188 kJ/d; P = 0. 07), but had higher 24RQ values, accounting for a 992 +/- 327-kJ/d lower 24-h fat oxidation rate (P < 0.005).


CONCLUSIONS
These data not only confirm the findings of a lower metabolic rate in African American than in white women, but also suggest that fat oxidation is lower in African American men than in white men.
Weyer
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Clinical Diabetes and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, AZ 85016, USA. cweyer@phx.niddk.nih.gov
Snitker
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S
Bogardus
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C
Ravussin
E
E
D000328:Adult; D001481:Basal Metabolism; D044383:Black People; D001823:Body Composition; D001824:Body Constitution; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000209:etiology*; D012307:Risk Factors; D012727:Sex Characteristics; D012890:Sleep; D044465:White People; D001741:Black or African American