Influence of dietary fatty acid composition and exercise on changes in fat oxidation from a high-fat diet
Journal Title (Medline/Pubmed accepted abbreviation): J. Appl. Physiol.
Year: 2010
Volume: 109
Page numbers: 1011-1018
doi (if applicable): 10.1152/japplphysiol.01025.2009

Summary of Background and Research Design

Background: When diet composition changes, the body requires time to adjust. It has been shown that it takes about 5-7 days for the rate of fat metabolism to increase when the diet shifts from moderate to high fat.

Hypothesis/Research Question: Does regular exercise decrease the time it takes for the body to adjust to a high fat diet? Does the type of fat (saturated vs. mono-unsaturated fat) affect the rate of adaptation?

Subjects: 8 healthy, sedentary men, age 18-45, BMI between 18-30 kg/m2

Experimental design: Randomized crossover

Treatments and protocol: Each participant underwent each of the 4 treatment conditions one time:
  • High saturated fat, sedentary
  • High saturated fat, exercise
  • High mono-unsaturated fat, sedentary
  • High mono-unsaturated fat, exercise
Each participant spent 5 days and 6 nights in a metabolic chamber with at least 2 wks separating each visit. Exercise visits included 2 x 1 hr stationary cycling sessions per day at 45% their VO2max. The precise exercise duration was calculated so that their 24 hr energy expenditure was equal to 1.8*RMR (resting metabolic rate).
Respiratory (or metabolic) chambers measure the amount of oxygen consumed and carbon dioxide exhaled by the individual by monitoring the precise changes of O2 and CO2 in the air.
Participants consumed isotopically labeled fatty acids on days 1 or 2 and day 5 in order to investigate fat oxidation (metabolism). These isotopes were monitored in urine (2H) or exhaled CO2 (13C). This technique confirms the metabolism of the specific fatty acids ingested and does not affect rate or extent of metabolism.
RMR, VO2, urinary nitrogen, energy expenditure (EE, calculated from CO2 uptake (VCO2), VO2, nonprotein respiratory exchange ratio (NPRER), and urinary nitrogen were measured

Summary of research findings:
  • It was confirmed that exercise shortens the time it takes for the body to adapt to a high fat diet
  • FA composition did not influence the rate at which 24-h fat oxidation increases
  • The nonprotein respiratory exchange ratio (NPRER) decreased following a switch from a standard to a high fat diet with habitual exercise. The type of fat does not affect the rate of the decrease.

Interpretation of findings/Key practice applications:

When a diet is changed to a high fat diet, it requires time for the metabolism to adjust regardless of the type of fat in the new diet. Exercise increases the rate of metabolic adaptation.
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