Body Fat has No Effect on the Maximal Fat Oxidation Rate in Young, Normal, and Overweight Women

Abstract

The purpose of this study was to examine how fat mass affects the maximal fat oxidation rates of women. Fourteen active, healthy women (age, 21-31 years) with body composition ranging from 18.6 to 30.0% fat were divided into 2 groups (15-24.9% = lower-fat group; 25-35% = higher-fat group). On day 1, subjects performed a graded exercise test on the treadmill to determine maximal oxygen consumption (VO2max). On day 2, subjects were measured for % fat and performed a maximal fat oxidation test. Fat and carbohydrate oxidation rates were determined using gas exchange analysis. Fat oxidation in absolute (in gram per minute) and relative to fat-free body mass (in milligram per kilogram of fat-free mass per minute) was determined using stoichiometric equations and appropriate energy equivalents. There were no significant differences (p > 0.05) in maximal fat oxidation rates between the women in lower-fat (0.39 ± 0.10 g·min-1, 8.52 ± 2.69 mg·kg FFM·min-1) and higher-fat (0.49 ± 0.13 g·min-1, 10.81 ± 2.80 mg·kg-1 FFM·min-1) groups. Maximal fat oxidation occurred at an exercise intensity of 55.7 ± 11.1% and 59.1 ± 5.4% VO2max for the lower-fat and higher-fat groups, respectively, with no significant difference between groups (p > 0.05). The maximal fat oxidation rate (g·min-1 and mg·kg-1 FFM·min-1) was not significantly correlated with any of the descriptive variables (fat mass, fat-free mass, percent body fat, or VO2max). In conclusion, personal trainers and health practitioners can use the exercise intensities that elicited the highest rate of fat oxidation to prescribe exercise programs to women, despite their body composition, that prevent weight gain and/or promote body fat and body weight loss.

Exercise Fat Oxidation Is Positively Associated with Body Fatness in Men with Obesity: Defying the Metabolic Flexibility Paradigm

“…On the other hand, the results of the present study differ with previous investigations performed on recreationally active overweight and lean subjects where MFO was not associated with body fatness [ 15 , 16 , 17 ]. Differences in the participants’ sex, body composition, physical activity level and experimental design, hinders comparison among studies result.…”

“…On the other hand, the sample size of the present study is similar to previous studies analyzing the association of MFO and body fatness (sample size range 14–54) [ 15 , 16 , 17 ], nonetheless, future large-cohort studies are needed to corroborate the here reported associations.…”

“…Differences in the participants’ sex, body composition, physical activity level and experimental design, hinders comparison among studies result. Furthermore, Blaize et al, [ 15 ] and Croci et al, [ 17 ] included data from lean and overweight subjects in the correlation analysis while only subjects with obesity where included in the present study. Moreover, these studies did not include VO 2max/peak as a covariate in their analysis which may bias their results.…”

“…Thereby, it is necessary to elucidate, whether these Metflex markers are associated and truly represent the capacity to use fat as a fuel during exercise. From the above-mentioned markers, only MFO has been directly associated with body fatness, without observing a significant relationship among other variables [ 15 , 16 , 17 ]. In these studies, CRF has not been considered as a covariate, which is associated with fat oxidation [ 16 , 17 ], and with metabolic syndrome in males and females [ 18 ].…”

Shorter recovery time following high-intensity interval training induced higher body fat loss among overweight women

“…Mannaing et al [40]. claimed that the initial level of blood lipids, being non-obese or the level of fat storage Blaize et al [41] may lead to the effectiveness of an exercise program that result in significant changes in blood lipid profiles. Therefore, in our study the activity level of the participants in 3 to 4 sessions of leisure activity per month, low sample size and duration of exercise program are limitations of the present study, and may be the reason that the measures of fatness other than fat % did not change significantly.…”