title: Concurrent physical activity increases fat oxidation during the shift to a high-fat diet.
abstract: BACKGROUND
  It takes several days to adapt to a high-fat diet. In an earlier study, we observed a large degree of interindividual variation in the capacity to adapt to a high-fat diet. We hypothesized that concurrent physical activity would accelerate fat oxidation during an isoenergetic high-fat diet.
  
  
  OBJECTIVE
  The objective of this study was to determine the effect of increased physical activity on the ability of young healthy men to increase fat oxidation during the shift to a high-fat diet.
  
  
  METHODS
  Six young healthy men participated in a randomized, single-blind crossover study. The volunteers consumed a diet contributing 37% of energy as fat, 14% as protein, and 49% as carbohydrate for 4 d. Energy expenditure and macronutrient balance were then measured in a respiration chamber as the energy content of the isoenergetic diet was changed to 50% fat, 14% protein, and 36% carbohydrate. Treadmill walking, as the physical activity, was used to increase total daily energy expenditure to 1.8 times the resting metabolic rate during 1 of 2 stays in the metabolic chamber. Total daily energy expenditure was maintained at 1.4 times the resting metabolic rate for the other stay.
  
  
  RESULTS
  Energy balance was not significantly different between the 2 conditions. The 24-h respiratory quotient decreased more rapidly and to a greater extent under conditions of increased energy expenditure. Further, there was a decrease in the interindividual variability in the response of the respiratory quotient to a high-fat diet with increased energy expenditure (physical activity). Cumulative carbohydrate and protein balances were greater under conditions of increased physical activity. Conversely, cumulative fat balance was greater under sedentary conditions.
  
  
  CONCLUSIONS
  Concurrent physical activity increases fat oxidation during the shift to a high-fat diet.
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA 70808, USA. smithsr@mhs.pbrc.edu
authors.forename: S R
authors.initials: SR
authors.lastname: Smith
authors.forename: L
authors.initials: L
authors.lastname: de Jonge
authors.forename: J J
authors.initials: JJ
authors.lastname: Zachwieja
authors.forename: H
authors.initials: H
authors.lastname: Roy
authors.forename: T
authors.initials: T
authors.lastname: Nguyen
authors.forename: J
authors.initials: J
authors.lastname: Rood
authors.forename: M
authors.initials: M
authors.lastname: Windhauser
authors.forename: J
authors.initials: J
authors.lastname: Volaufova
authors.forename: G A
authors.initials: GA
authors.lastname: Bray
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001823:Body Composition; D018592:Cross-Over Studies; D004041:Dietary Fats / Q000008:administration & dosage* / Q000378:metabolism*; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction; D012016:Reference Values; D012119:Respiration; D012146:Rest; D016037:Single-Blind Method
chemical_list: D004041:Dietary Fats