Effects of adipose tissue distribution on maximum lipid oxidation rate during exercise in normal-weight women

Biomarkers and genetic polymorphisms associated with maximal fat oxidation during physical exercise: implications for metabolic health and sports performance

The maximal fat oxidation rate (MFO) assessed during a graded exercise test is a remarkable physiological indicator associated with metabolic flexibility, body weight loss and endurance performance. The present review considers existing biomarkers related to MFO, highlighting the validity of maximal oxygen uptake and free fatty acid availability for predicting MFO in athletes and healthy individuals. Moreover, we emphasize the role of different key enzymes and structural proteins that regulate adipose tissue lipolysis (i.e., triacylglycerol lipase, hormone sensitive lipase, perilipin 1), fatty acid trafficking (i.e., fatty acid translocase cluster of differentiation 36) and skeletal muscle oxidative capacity (i.e., citrate synthase and mitochondrial respiratory chain complexes II-V) on MFO variation. Likewise, we discuss the association of MFO with different polymorphism on the ACE, ADRB3, AR and CD36 genes, identifying prospective studies that will help to elucidate the mechanisms behind such associations. In addition, we highlight existing evidence that contradict the paradigm of a higher MFO in women due to ovarian hormones activity and highlight current gaps regarding endocrine function and MFO relationship.

Determinants of Peak Fat Oxidation Rates During Cycling in Healthy Men and Women

This study explored lifestyle and biological determinants of peak fat oxidation (PFO) during cycle ergometry, using duplicate measures to account for day-to-day variation. Seventy-three healthy adults (age range: 19-63 years; peak oxygen consumption [V˙O2peak]: 42.4 [10.1] ml·kg BM-1·min-1; n = 32 women]) completed trials 7-28 days apart that assessed resting metabolic rate, a resting venous blood sample, and PFO by indirect calorimetry during an incremental cycling test. Habitual physical activity (combined heart rate accelerometer) and dietary intake (weighed record) were assessed before the first trial. Body composition was assessed 2-7 days after the second identical trial by dual-energy X-ray absorptiometry scan. Multiple linear regressions were performed to identify determinants of PFO (mean of two cycle tests). A total variance of 79% in absolute PFO (g·min-1) was explained with positive coefficients for V˙O2peak (strongest predictor), FATmax (i.e the % of V˙O2peak that PFO occurred at), and resting fat oxidation rate (g·min-1), and negative coefficients for body fat mass (kg) and habitual physical activity level. When expressed relative to fat-free mass, 64% of variance in PFO was explained: positive coefficients for FATmax (strongest predictor), V˙O2peak, and resting fat oxidation rate, and negative coefficients for male sex and fat mass. This duplicate design revealed that biological and lifestyle factors explain a large proportion of variance in PFO during incremental cycling. After accounting for day-to-day variation in PFO, V˙O2peak and FATmax were strong and consistent predictors of PFO.

Effect of Fat Mass Localization on Fat Oxidation During Endurance Exercise in Women

Independent of total body fat mass, predominant upper body fat mass distribution is strongly associated with cardio-metabolic comorbidities. However, the mechanisms underlying fat mass localization are not fully understood. Although a large body of evidence indicates sex-specific fat mass distribution, women are still excluded from many physiological studies and their specific features have been investigated only in few studies. Moreover, endurance exercise is an effective strategy for improving fat oxidation, suggesting that regular endurance exercise could contribute to the management of body composition and metabolic health. However, no firm conclusion has been reached on the effect of fat mass localization on fat oxidation during endurance exercise. By analyzing the available literature, this review wants to determine the effect of fat mass localization on fat oxidation rate during endurance exercise in women, and to identify future research directions to advance our knowledge on this topic. Despite a relatively limited level of evidence, the analyzed studies indicate that fat oxidation during endurance exercise is higher in women with lower upper-to-lower-body fat mass ratio than in women with higher upper-to-lower-body fat mass ratio. Interestingly, obesity may blunt the specific effect of upper and lower body fat mass distribution on fat oxidation observed in women with normal weight during endurance exercise. Studying and understanding the physiological responses of women to exercise are essential to develop appropriate physical activity strategies and ultimately to improve the prevention and treatment of cardio-metabolic diseases.

No Influence of Overweight/Obesity on Exercise Lipid Oxidation: A Systematic Review

Compared to lean counterparts, overweight/obese individuals rely less on lipid during fasting. This deficiency has been implicated in the association between overweight/obesity and blunted insulin signaling via elevated intramuscular triglycerides. However, the capacity for overweight/obese individuals to use lipid during exercise is unclear. This review was conducted to formulate a consensus regarding the influence of overweight/obesity on exercise lipid use. PubMed, ProQuest, ISI Web of Science, and Cochrane Library databases were searched. Articles were included if they presented original research on the influence of overweight/obesity on exercise fuel use in generally healthy sedentary adults. Articles were excluded if they assessed older adults, individuals with chronic disease, and/or exercise limitations or physically-active individuals. The search identified 1205 articles with 729 considered for inclusion after duplicate removal. Once titles, abstracts, and/or manuscripts were assessed, 24 articles were included. The preponderance of evidence from these articles indicates that overweight/obese individuals rely on lipid to a similar extent during exercise. However, conflicting findings were found in eight articles due to the outcome measure cited, participant characteristics other than overweight/obesity and characteristics of the exercise bout(s). We also identified factors other than body fatness which can influence exercise lipid oxidation that should be controlled in future research.

Evaluation of a graded exercise test to determine peak fat oxidation in individuals with low cardiorespiratory fitness

The maximal capacity to utilise fat (peak fat oxidation, PFO) may have implications for health and ultra-endurance performance and is commonly determined by incremental exercise tests employing 3-min stages. However, 3-min stages may be insufficient to attain steady-state gas kinetics, compromising test validity. We assessed whether 4-min stages produce steady-state gas exchange and reliable PFO estimates in adults with peak oxygen consumption < 40 mL·kg−1·min−1. Fifteen participants (9 females) completed a graded test to determine PFO and the intensity at which this occurred (FATMAX). Three short continuous exercise sessions (SCE) were then completed in a randomised order, involving completion of the graded test to the stage (i) preceding, (ii) equal to (SCEequal), or (iii) after the stage at which PFO was previously attained, whereupon participants then continued to cycle for 10 min at that respective intensity. Expired gases were sampled at minutes 3–4, 5–6, 7–8, and 9–10. Individual data showed steady-state gas exchange was achieved within 4 min during SCEequal. Mean fat oxidation rates were not different across time within SCEequal nor compared with the graded test at FATMAX (both p > 0.05). However, the graded test displayed poor surrogate validity (SCEequal, minutes 3–4 vs. 5–6, 7–8, and 9–10) and day-to-day reliability (minutes 3–4, SCEequal vs. graded test) to determine PFO, as evident by correlations (range: 0.47–0.83) and typical errors and 95% limits of agreement (ranges: 0.03–0.05 and ±0.09–0.15 g·min−1, respectively). In conclusion, intraindividual variation in PFO is substantial despite 4-min stages establishing steady-state gas exchange in individuals with low fitness. Individual assessment of PFO may require multiple assessments.

Inhibitory Effects of Intranasal Administration of Insulin on Fat Oxidation during Exercise Are Diminished in Young Overweight Individuals

It remains unknown whether the high insulin (INS) levels in the brain affect fat oxidation during exercise. We examined the effects of the intranasal administration of INS, which increases the INS concentration in the cerebrospinal fluid when peripheral effects are lacking, on the maximum fat oxidation rate (maxFOR) and its intensity (FATmax) during exercise in 15 young normal-weight (N group) and eight young overweight (O group) individuals. On two separate days, either INS or placebo (PL) was randomly administered intranasally before a graded exercise test. Indirect calorimetry was used to assess maxFOR and FATmax during exercise. Blood INS and glucose levels did not change after INS administration. In the N group, maxFOR and FATmax were significantly smaller in the INS trial than in the PL trial. MaxFOR was significantly smaller in the O group than in the N group and was not influenced by INS administration. Exercise-induced elevation in blood epinephrine levels tended to be reduced by INS administration only in the N group. Intranasal INS administration reduces fat oxidation during exercise without any peripheral effects, possibly by suppressing sympathetic nerve activity. This inhibitory effect is diminished in overweight subjects, suggesting that cerebral insulin effects are attenuated in this population.

A nutrition and conditioning intervention for natural bodybuilding contest preparation: case study

Bodybuilding competitions are becoming increasingly popular. Competitors are judged on their aesthetic appearance and usually exhibit a high level of muscularity and symmetry and low levels of body fat. Commonly used techniques to improve physique during the preparation phase before competitions include dehydration, periods of prolonged fasting, severe caloric restriction, excessive cardiovascular exercise and inappropriate use of diuretics and anabolic steroids. In contrast, this case study documents a structured nutrition and conditioning intervention followed by a 21 year-old amateur bodybuilding competitor to improve body composition, resting and exercise fat oxidation, and muscular strength that does not involve use of any of the above mentioned methods. Over a 14-week period, the Athlete was provided with a scientifically designed nutrition and conditioning plan that encouraged him to (i) consume a variety of foods; (ii) not neglect any macronutrient groups; (iii) exercise regularly but not excessively and; (iv) incorporate rest days into his conditioning regime. This strategy resulted in a body mass loss of 11.7 kg’s, corresponding to a 6.7 kg reduction in fat mass and a 5.0 kg reduction in fat-free mass. Resting metabolic rate decreased from 1993 kcal/d to 1814 kcal/d, whereas resting fat oxidation increased from 0.04 g/min to 0.06 g/min. His capacity to oxidize fat during exercise increased more than two-fold from 0.24 g/min to 0.59 g/min, while there was a near 3-fold increase in the corresponding exercise intensity that elicited the maximal rate of fat oxidation; 21% V̇O_2max to 60% V̇O_2max. Hamstring concentric peak torque decreased (1.7 to 1.5 Nm/kg), whereas hamstring eccentric (2.0 Nm/kg to 2.9 Nm/kg), quadriceps concentric (3.4 Nm/kg to 3.7 Nm/kg) and quadriceps eccentric (4.9 Nm/kg to 5.7 Nm/kg) peak torque all increased. Psychological mood-state (BRUMS scale) was not negatively influenced by the intervention and all values relating to the Athlete’s mood-state remained below average over the course of study. This intervention shows that a structured and scientifically supported nutrition strategy can be implemented to improve parameters relevant to bodybuilding competition and importantly the health of competitors, therefore questioning the conventional practices of bodybuilding preparation.

Maximal fat oxidation, but not aerobic capacity, is affected by oral contraceptive use in young healthy women

PURPOSE

Synthetic ovarian hormones contained in oral contraceptives (OC) may alter the aerobic capacity and lipid metabolism in oral contraceptive users (OC+) compared with non-users (OC-). The aim of this study was thus to investigate the differences between OC- and OC+ (1) in cardiorespiratory parameters at the anaerobic threshold (AT) and at the maximal aerobic capacity and (2) in the exercise intensity (Lipoxmax) at which lipid oxidation rate is maximal (MLOR).

METHODS

Twenty-one healthy untrained women (22.0 ± 0.6 years old) who took OC (OC+; low-dose monophasic OC, n = 11) or not (OC-; n = 10) performed two experimental exercise sessions. In the first one, cardiorespiratory parameters at the AT and at the maximal aerobic capacity were assessed during a maximal incremental exercise session. In the second one, Lipoxmax and MLOR were measured during a submaximal incremental exercise session.

RESULTS

No significant difference was observed in cardiorespiratory parameters at the AT and at the maximal aerobic capacity between OC+ and OC- women. OC+ women showed higher MLOR (7.6 ± 1.9 vs 4.6 ± 1.0 mg min(-1) kg FFM(-1); p < 0.01) that was elicited by higher Lipoxmax (45.2 ± 5.2 vs 36.2 ± 4.1 % of VO2max; p < 0.001) compared to OC- women.

CONCLUSIONS

OC+ and OC- women did not differ in cardiorespiratory parameters at the AT and at the maximal aerobic capacity. However, OC+ women show higher MLOR and Lipoxmax compared with OC- women. The hormonal status appears to be an important MLOR and Lipoxmax determinant in untrained women.