Journal Title (Medline/Pubmed accepted abbreviation): J. Appl. Physiol.
Page numbers: 1607-1614
doi (if applicable): 10.1152/japplphysiol.01341.2010
Summary of Background and Research Design
Background:Low carbohydrate-high fat diets likely alter the gene expression in the mitochondria, leading to higher rates of fat oxidation during exercise, with a smaller reliance on glycogen and carbohydrate.
Hypothesis:A high fat diet will affect substrate metabolism in the mitochondria during exercise. Also, a high fat diet will not affect insulin sensitivity.
Subjects:21 untrained university students, age about 22-25
Experimental design:randomized, cross over
Treatments:Normal diet: 25-35% of energy from fat, 55-60% carbohydrate, and 10-15% protein;
High fat diet: 55-60% of energy from fat, 25-30% carbohydrate, and 15% protein
Protocol:On day 0, subjects arrived to the laboratory fasted, where their body composition and VO2max were determined and a muscle biopsy (vastus lateralis = outer thigh) was acquired. Resting amounts of oxygen consumption and carbon dioxide exhalation were also determined. They then were randomly assigned to consume the normal or the high fat diet from days 1-15. On day 15, the same measurements were repeated as on day 0. In addition, insulin sensitivity was determined using a hyperinsulinemic-euglycemic clamp method. On day 16, the subjects cycled on a stationary bicycle at 70% of their VO2max for 60 min (plus a warm up of 40% VO2max for 7 min). Muscle biopsies were acquired before and after exercise, and blood was drawn at determined intervals. The muscle biopsies were used to determine mitochondrial oxygen consumption, mitochondrial respiration, muscle glycogen and fat content, quantities of different metabolic enzymes, and total and mitochondrial DNA content.
Summary of research findings:
- The protein intake was a little higher than the specified goal for the normal diet group (17.6 ± 0.7%), and the carbohydrate intake was slightly higher than the specified goal in the high fat group (31.8 ± 2.1%). The fat intake was on target for both groups.
- Fasting plasma glucose and insulin concentrations were similar for both groups and insulin sensitivity did not appear to be affected by the diet intervention.
- Triacylglycerol and glycogen content in the muscle was similar for both groups. Glycogen decreased significantly to a similar extent for both groups.
- Mitochondrial respiration was slightly different during exercise between the 2 groups; it appeared that the flux through the electron transport chain (generates ATP with oxygen) was more efficient for people with the normal diet compared to the high fat diet. More specifically, state 3 respiration, measured when both ADP and glycolytic substrates are high, was increased during exercise much more significantly in the people who were on the normal diet compared to those that were on the high fat diet.
- There were decreases in the expression of proteins from complex I (P < 0.05) and complex IV (P = 0.06) with the high fat versus normal diet. Complex V (i.e., ATP synthase) protein was also significantly lower on the high fat vs. normal diet (P < 0.05) and there was a similar decline in complex III protein that did not quite reach statistical significance (P = 0.057).
- Those who had consumed the high fat diet showed an increase in respiration rates for a longer time into the recovery period than the people on the normal diet.
Interpretation of findings/Key practice applications:
Even in the absence of effects on insulin sensitivity or intramyocellular lipid accumulation, a high fat diet tended to negate some of exercise-induced changes in mitochondrial respiratory flux compared with a “normal” diet. Such changes could potentially adversely impact the ability of an athlete to generate ATP during exercise. However, exercise performance was not measured in this study, so it is not clear what impact the high fat diet period might have had on exercise performance.
It would have been interesting if the exercise performance was monitored.