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34. Ingested fat oxidation contributes 8% of 24-h total energy expenditure in moderately obese subjects

Author

Sonko, Bakary J., Fennessey, Paul V., Donnelly, Joseph E., Bessesen, Daniel, Sharp, Teresa A., Jacobsen, Dennis J., Jones, Richard H., and Hill, James O.

Subjects
Food/cooking/nutrition
Abstract

The role of ingested fat in the etiology of obesity is controversial. The aims of this study were to determine the contributions of ingested fat oxidation to: 1) 24-h total energy expenditure (TEE), and 2) substrate oxidation during acute stationary cycle exercises in adult humans. Healthy, moderately obese (n = 18; BMI = 31 [+ or -] 1 kg/[m.sup.2]) subjects (8 men; 10 women) were each studied in a whole-room calorimeter for 24 h. They were fed mixed meals (55, 30, and 15% as energy from carbohydrate, fat and protein, respectively) to maintain energy balance. Each subject performed 1255-kJ cycle exercises at 50% V[O.sub.2max] in the calorimeter. Study test meal fat was labeled with carbon-13 ([sup.13]C). Ingested fat oxidation was estimated from breath [sup.13]C[O.sub.2] excretion and the subject's chamber C[O.sub.2] production. Total fat and carbohydrate oxidations were estimated from nonprotein respiratory quotient (NP-RQ) values. Endogenous fat oxidation was estimated as the difference between total fat and ingested fat oxidations. TEE was estimated from gas exchanges; 28 [+ or -] 3% of ingested fat was oxidized and it provided 8 [+ or -] 1% of 24-h TEE. During cycle exercises, ingested fat provided 50% of total fat oxidized and 13.0 [+ or -] 2% of energy expended. Endogenous fat oxidation contributed 10.4 [+ or -] 3% of energy expenditure during cycle exercises. This study extended to 24-h observations of previous studies that lasted 6-9 h on ingested fat oxidation in humans. Understanding the factors that promote ingested fat oxidation could lead to more effective obesity intervention programs. KEY WORDS: * fat * oxidation * mixed-meals * obesity

Published
2005

46. Improving power with repeated measures: diet and serum lipids

Author

Marshall, Julie A., Scarbro, Sharon, Shetterly, Susan M., and Jones, Richard H.

Subjects
Blood lipids -- Measurement, Diet -- Physiological aspects, Epidemiological research -- Methods, Food/cooking/nutrition, Health
Abstract

The inability to detect associations between diet and serum cholesterol in cross-sectional population studies has been attributed to measurement error in diet assessments and between-subject variability in lipid concentrations. Current statistical methods can reduce the effects of measurement error and allow within-subject comparisons when replicate measures on individuals are available, even if the time between replicates is as long as 4 y and replicate data are not available for all subjects. Data from 928 nondiabetic participants of the San Luis Valley Diabetes Study with measures of 24-h dietary intake and fasting lipid concentrations at baseline, at a 4-y follow-up visit, or both were analyzed in a random-effects model that allowed for an unbalanced design. Sex was included as a non-time-varying covariate and age, body mass index, and energy intake were included as time-varying covariates. The findings when LDL cholesterol (mmol/L) was regressed on saturated fat intake (20 g/d) with all observations in a random-effects model ([Beta] = 0.14, P = 0.0016) were compared with results with observations restricted to the first visit only ([Beta] = 0.05, P = 0.52), a balanced design using averages across visits ([Beta] = -0.12, P = 0.28), and a balanced design with random effects obtained by excluding subjects without two observations ([Beta] = 0.12, P = 0.0092). Study power was greatest in the random-effects model using all observations and time-varying covariates. These findings highlight the importance of even a single replicate observation on a subsample of subjects. We recommend analyzing all data rather than averaging measures across visits or omitting observations to create a balanced design. Am J Clin Nutr 1998;67:934-9.

Published
1998

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