Associations Among Dietary Fat Oxidation Responses to Overfeeding and Weight Gain in Obesity-Prone and Resistant Adults

Abstract

Objective: This study tested the hypothesis that 3 days of overfeeding (OF) decreases dietary fat oxidation and predicts longitudinal weight change in adults classified as obesity prone (OP) and obesity resistant (OR) based on self-identification and personal and family weight history. Changes in diurnal profiles of plasma metabolites and hormones were measured to probe mechanisms.

Methods: Adults identified as OP (n = 22; BMI: 23.9 ± 2.4 kg/m² ) and OR (n = 30; BMI: 20.5 ± 2.2 kg/m² ) completed 3 days of eucaloric (EU) feeding and 3 days of OF. On day 3, the 24-hour total and dietary fat oxidation was measured using room calorimetry and an oral ¹⁴ C tracer. Plasma glucose, insulin, triglycerides, and nonesterified fatty acid (NEFA) concentrations were frequently sampled over 24 hours. Body composition was measured annually for 4.0 ± 1.4 years in a subsample (n = 19 OP and 23 OR).

Results: Dietary fat oxidation over 24 hours was not altered by OF versus EU (P = 0.54). Weight gain in OP correlated with lower nocturnal NEFA concentrations during OF (r = -0.60; P = 0.006) and impaired fuel selection over 24 hours (metabolic inflexibility, wake respiratory quotient-sleep respiratory quotient) (r = -0.48; P = 0.04).

Conclusions: Short-term OF did not alter dietary fat oxidation. Lower nocturnal NEFA availability and metabolic inflexibility to overfeeding may be factors contributing to weight gain.

Trial registration: ClinicalTrials.gov NCT00072917.

FIGURE 1.

Total fat oxidation (A), absolute dietary fat oxidation (grams of meal fat oxidized, B), and relative dietary fat oxidation (percentage of tracer dose, C) during the eucaloric (EU) and overfed (OF) conditions in OP and OR adults. Data are means ± SEM. Arrows indicate the time of breakfast, lunch, and dinner consumption, respectively. The grey area represents night time.

FIGURE 2.

Twenty-four-hour (bar height), daytime (open area), and nocturnal (hatched area) values for total fat oxidation (A), absolute and relative dietary fat oxidation (B), and dietary fat oxidation normalized to total fat oxidation (C) during the eucaloric (EU) and overfed (OF) conditions in OP and OR adults. Data are means ± SEM. * significantly different between feeding conditions, P < 0.05.

FIGURE 3.

Metabolic flexibility as measured by room calorimetry (awake npRQ – sleep npRQ) during the eucaloric (EU) and overfed (OF) conditions in OP and OR adults.

FIGURE 4.

Plasma glucose (A), insulin (B), triglyceride (TG) (C), and non-esterified fatty acid (NEFA) (D) concentrations during the eucaloric (EU) and overfed (OF) conditions in OP and OR adults. Data are means ± SEM. Arrows indicate the time of breakfast, lunch, and dinner consumption, respectively. The grey area represents night time.

FIGURE 5.

Twenty-four-hour, daytime, and nocturnal areas under the curve for plasma glucose (A), insulin (B), triglycerides (TG) (C), and non-esterified fatty acids (NEFA) (D) during the eucaloric (EU) and overfed (OF) conditions in OP and OR adults. Data are means ± SEM. * significantly different between feeding conditions, P < 0.05. ^# significant group x condition interaction, P<0.05.

FIGURE 6.

Correlations between responses to 3 days of overfeeding (Δ response= overfed – eucaloric condition) and the rate of weight change (RoWC) during follow-up. A reduction in nocturnal fat oxidation (A and B), metabolic flexibility (MF) (C and D), increased reliance on meal fat at night (E and F) and reduced plasma non-esterified fatty acid availability (G and H) were predictors of the RoWC in OP but not OR participants (r-values and P-values shown in each panel). Correlation coefficients for the combined sample are shown in Supplemental Figure 1.