A High-Fat Compared With A High-Carbohydrate Breakfast Enhances 24-Hour Fat Oxidation In Older Adults

Background: The ability to oxidize fat is associated with a lower risk of chronic metabolic disease. Preclinical data in mice showed that a high-fat "breakfast" increased 24-h fat oxidation relative to a high-carbohydrate breakfast.Objectives: The objectives of this study were to determine whether the timing of macronutrient intake in humans affects daily fuel utilization and to examine associations between fuel utilization and metabolic indexes.Methods: Participants were 29 healthy sedentary men and women (aged 55-75 y) with a body mass index (kg/m(2)) between 25 and 35. Participants were randomly assigned to receive either a high-fat breakfast (FB; 35% carbohydrate, 20% protein, 45% fat; n = 13) or a high-carbohydrate breakfast (CB; 60% carbohydrate, 20% protein, 20% fat; n = 16) for 4 wk while consuming a "neutral" lunch and dinner. Twenty-four-hour and postprandial respiratory quotients (RQs) were measured by whole-room indirect calorimetry. Insulin and glucose measures including insulin sensitivity were determined by an oral-glucose-tolerance test. Measures were taken at baseline and after the 4-wk intervention. Group-by-time interactions were determined by 2-factor repeated-measures mixed-model ANOVA. Pearson's correlation analyses were used to determine associations of 24-h RQs with metabolic measures after the intervention.Results: There was a significant group-by-time interaction for change in the 24-h RQ [ FB (mean +/- SD): 0.88 +/- 0.02 to 0.86 +/- 0.02; CB: 0.88 +/- 0.02 for both; P < 0.05], breakfast RQ (FB: 0.88 +/- 0.03 to 0.86 +/- 0.03; CB: 0.89 +/- 0.02 to 0.90 +/- 0.02; P < 0.01), and lunch RQ (FB: 0.089 +/- 0.03 to 0.85 +/- 0.03; CB: 0.89 +/- 0.03 for both; P < 0.01). In the CB group at follow-up, 24-h RQ was positively associated with fasting glucose (r = 0.66, P < 0.05), glucose area under the curve (AUC) (r = 0.51, P < 0.05), and insulin AUC (r = 0.52, P < 0.05) and inversely associated with insulin sensitivity (r = -0.51, P < 0.05).Conclusions: The macronutrient composition of breakfast affects substrate utilization throughout the day in older adults. The consumption of a high-fat, lower-carbohydrate breakfast may reduce the risk of metabolic disease.