ORIGINAL ARTICLE Effect of gender on fuel utilization during exercise at different intensities in untrained Thai individuals Taweesak Janyacharoen Æ Paradee Auvichayapat Æ Kostas Tsintzas Æ Ian A. Macdonald Æ Naruemon Leelayuwat Accepted: 7 August 2009 / Published online: 28 August 2009 Ó Springer-Verlag 2009 Abstract Research in Western populations has demon- strated a gender effect on substrate metabolism during exercise. Women have been shown to use more lipid and less carbohydrate as energy sources during endurance exercise, compared with their male counterparts. Nutri- tional status influences fuel utilization during exercise. Thai men and women routinely ingest a greater proportion of their dietary energy as carbohydrate than Caucasian individuals and thus may respond differently to exercise. Therefore, this study aimed to investigate the effects of gender on fuel utilization at different exercise intensities in untrained Thai individuals. Sixteen healthy sedentary men and 16 women participated in this study. All participants cycled at a target workload equivalent to 25, 65 and 85% maximum oxygen consumption continuously for 15, 10 and 10 min, respectively. Expired gas samples were col- lected for 30 min at rest and for the final 5 min of each exercise intensity. Actual relative exercise intensities were 32 ± 1.7, 64 ± 1.8, 84 ± 1.7% maximum oxygen con- sumption, respectively, and there was no significant dif- ference between genders. Carbohydrate oxidation rate was higher than fat oxidation rate at every exercise intensity in both genders. In untrained Thai individuals, gender did not affect fuel utilization during sub-maximal exercise. The higher utilization of carbohydrate than fat at rest and during exercise in Thai individuals than seen previously in other populations may be due to the Thai’s habitual higher die- tary carbohydrate intake. Keywords Exercise  Gender  Metabolism  Ethnic group Introduction Women were shown to use more fat during prolonged exercise than men (Carter et al. 2001; Tarnopolsky 2000; Davis et al. 2000). Previously, these authors suggested that circulating levels of oestrogen and progesterone are likely to play an important role in explaining the gender differ- ence in substrate utilization during exercise. It was con- cluded that estradiol supplementation alters fuel selection during exercise by increasing lipid use and reducing car- bohydrate (blood glucose) use (Devries et al. 2005; Tar- nopolsky 2008). Moreover, previous studies have demonstrated that the utilization of fat and carbohydrate (CHO) (which are important fuels for ATP synthesis in human skeletal muscle during exercise) depends strongly on exercise intensity (Romijn et al. 1993; van Loon et al. 2001). Taken together with the ‘‘Crossover’’ concept (Brooks and Mercier 1994), it was shown that fat utiliza- tion increases when the exercise intensity increases from low to moderate and decreases when the intensity becomes higher. The higher that exercise intensity is the more CHO is used by the muscle. Moreover, nutritional status also influences fuel utilization during exercise (Achten and Jeukendrup 2004; Jeukendrup 2003; Coyle et al. 2001). T. Janyacharoen Division of Physiotherapy, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen 40002, Thailand P. Auvichayapat  N. Leelayuwat (&) Department of Physiology, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand e-mail: naruemon@kku.ac.th K. Tsintzas  I. A. Macdonald Centre for Integrated Biology and Medicine, Institute of Clinical Research, University of Nottingham Medical School, Nottingham, UK 123 Eur J Appl Physiol (2009) 107:645–651 DOI 10.1007/s00421-009-1167-6