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Obesity (Silver Spring). 2011 Feb;19(2):319-23. doi: 10.1038/oby.2010.206. Epub 2010 Sep 23.

Higher 24-h respiratory quotient and higher spontaneous physical activity in nighttime eaters.

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  • 1Obesity and Diabetes Clinical Research Section, Phoenix Epidemiology and Clinical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona, USA.


We have previously shown that a higher 24-h respiratory quotient (24-h RQ) predicts greater ad-libitum food intake and that nighttime eaters (NE) ingested more calories during an in-patient food intake study and gained more weight over time. We investigated whether 24-h RQ was higher in individuals who exhibited nighttime eating behavior. Healthy nondiabetic Pima Indians (PI; n = 97, 54 male/43 female) and whites (W; n = 32, 22 male/10 female) were admitted to our Clinical Research Unit. After 3 days of a weight maintaining diet, 24-h energy expenditure (24-h EE), 24-h RQ, rates of carbohydrate (CHOX) and lipid oxidation (LIPOX), and spontaneous physical activity (SPA) were measured in a metabolic chamber whereas volunteers were in energy balance and unable to consume excess calories. Individuals subsequently ate ad libitum from a computerized vending machine for 3 days with amount and timing of food intake recorded. Fifty-five individuals (36%; 39 PI, 16 W) were NE, who ate between 11 PM and 5 AM on at least one of the 3 days on the vending machines. There were no differences in BMI or percentage body fat between NE and non-NE. After adjusting for age, sex, race, fat-free mass, fat mass, and energy balance, NE had a higher 24-h RQ (P = 0.01), higher CHOX (P = 0.009), and lower LIPOX (P = 0.03) and higher 24-h SPA (P = 0.04) compared to non-NE. There were no differences in adjusted 24-h EE or sleep RQ between the groups. Individuals with nighttime eating behavior have higher 24-h RQ, higher CHOX and lower LIPOX, a phenotype associated with increased food intake and weight gain.

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