June 7, 2015

Ilaria Crociab, Ingrid J Hickmanacd, Rachel E Woode, Fabio Borrani,fGraeme A Macdonald,gh Nuala M Byrneei

  1. The University of Queensland Diamantina Institute, Translational Research Institute, Brisbane, St Lucia QLD 4072, Australia.
  2. bSchool of Human Movement Studies, University of Queensland, Brisbane, St Lucia QLD 4072, Australia.
  3. Department of Nutrition and Dietetics, Princess Alexandra Hospital, Brisbane, St Lucia QLD 4072, Australia.
  4. Mater Medical Research Institute, Brisbane, St Lucia QLD 4072, Australia.
  5. School of Exercise and Nutrition Sciences, and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, St Lucia QLD 4072, Australia.
  6. Institute of Sport Sciences (ISSUL), University of Lausanne, CH-1015 Lausanne, Switzerland.
  7. School of Medicine, The University of Queensland, St Lucia QLD 4072, Australia.
  8. Department of Gastroenterology and Hepatology, Princess Alexandra Hospital, Brisbane, St Lucia QLD 4072, Australia.
  9. Bond Institute of Health and Sport, Bond University, Robina QLD 4226, Australia.

Lipids and carbohydrates are the two main fuels that sustain oxidative metabolism. Reduced whole-body fat oxidation at rest and during exercise are associated with negative metabolic outcomes such as insulin resistance. The determination of fat oxidation rates at rest and during exercise can inform prescription of exercise training programs (Venables and Jeukendrup 2008), provide insights into mechanisms of disease development and progression (Croci et al. 2013) and elucidate mechanisms of treatment options (Goodpaster et al. 2003).

Although there has been growing interest in understanding the independent roles of cardiorespiratory fitness and body fatness on health outcomes (fitness versus fatness debate), their relative importance on fat oxidation during exercise have not been fully elucidated. The maximal fat oxidation rate (MFO), as well as the exercise intensity at which it occurs (Fatmax) (Achten et al. 2002), have been reported as lower in sedentary overweight (Perez-Martin et al. 2001) but have not been studied in trained overweight individuals. Trained overweight individuals represent a population, which could particularly benefit from a more precise exercise prescription. They have already overcome the barrier of initiating or maintaining a physically active lifestyle, which is recognized as one of the major issues in training prescription for overweight individuals (Byrne et al. 2006).

The aim of this study (Croci et al. 2014) was to compare Fatmax and MFO in lean and overweight recreationally trained males matched for cardiorespiratory fitness and to study the relationships between these variables, body composition and cardiorespiratory fitness. Twelve recreationally trained overweight (30.0±5.3 % body fat) and twelve lean males (17.2±5.7 % body fat) matched for cardiorespiratory fitness and age performed a graded exercise test on a cycle ergometer. Maximal oxygen consumption, and fat and carbohydrate oxidation rates were determined using indirect calorimetry. It was found that MFO, Fatmax and fat oxidation rates over a wide range of exercise intensities were not different between overweight and lean groups. In the overall cohort of twenty-four participants, MFO and Fatmax were correlated with cardiorespiratory fitness, but not with % body fat or body mass index. In summary, fat oxidation during exercise was similar in recreationally trained overweight and lean males matched for cardiorespiratory fitness. Consistently, fat oxidation during exercise was related to fitness but not to fatness. The results of the present study highlight the importance of educating overweight individuals on the benefits of improving cardiorespiratory fitness independent of body weight or percentage body fat. Improvements in cardiorespiratory fitness will lead to greater fat oxidation during exercise and improved metabolic profile.

  • Achten, J., Gleeson, M., and Jeukendrup, A.E. 2002. Determination of the exercise intensity that elicits maximal fat oxidation. Med. Sci. Sports Exerc. 34(1): 92-97.
  • Byrne, N.M., Meerkin, J.D., Laukkanen, R., Ross, R., Fogelholm, M., and Hills, A.P. 2006. Weight loss strategies for obese adults: personalized weight management program vs. standard care. Obesity (Silver Spring). 14(10): 1777-1788.
  • Croci, I., Hickman, I.J., Wood, R.E., Borrani, F., Macdonald, G.A., and Byrne, N.M. 2014. Fat oxidation over a range of exercise intensities: fitness versus fatness. Appl. Physiol. Nutr. Metab. 39(12): 1352-1359.
  • Croci, I., Byrne, N.M., Choquette, S., Hills, A.P., Chachay, V.S., Clouston, A.D., O’Moore-Sullivan, T.M., Macdonald, G.A., Prins, J.B., and Hickman, I.J. 2013. Whole-body substrate metabolism is associated with disease severity in patients with non-alcoholic fatty liver disease. Gut. 62(11): 1625-1633.
  • Goodpaster, B.H., Katsiaras, A., and Kelley, D.E. 2003. Enhanced fat oxidation through physical activity is associated with improvements in insulin sensitivity in obesity. Diabetes. 52(9): 2191-2197.
  • Perez-Martin, A., Dumortier, M., Raynaud, E., Brun, J.F., Fedou, C., Bringer, J., and Mercier, J. 2001. Balance of substrate oxidation during submaximal exercise in lean and obese people. Diabetes Metab. 27(4 Pt 1): 466-474.
  • Venables, M.C. and Jeukendrup, A.E. 2008. Endurance training and obesity: effect on substrate metabolism and insulin sensitivity. Med. Sci. Sports Exerc. 40(3): 495-502.

If you intend citing any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.