ABC | Volume 115, Nº2, August 2020

Original Article Basilio et al. Effects of intermittent fasting on the heart Arq Bras Cardiol. 2020; 115(2):184-193 Despite glycemic effects, intermittent fasting did not alter functional fitness. Lactate measurement is one of the parameters most used to estimate aerobic capacity and has been effective to describe functional fitness. 22 The lactate threshold can be defined as the exercise intensity at which the blood lactate concentration suddenly increases. 21,22 In this respect, the running protocol improved functional fitness in the ET and ETI groups, which was supported by lower final lactate values (LacE), less variation in lactate levels and higher speed and distance covered during the final test. Therefore, exercise training was associated with improved aerobic fitness, as previously demonstrated. 16 Regarding cardiovascular features, exercise training promoted myocardial interstitial remodeling. Intriguingly, intermittent fasting attenuated these exercise-induced effects, as demonstrated by lower values of tissue macro- and microscopic morphometry in the ETI group. Multiple factors stimulate myocardial remodeling, such as nutritional disorders, angiotensin, aldosterone, endothelin, inflammatory cytokines and catecholamines. 36 Morphological and functional changes occur in response to prolonged exercise training in order to improve cardiac performance, including the blood volume pumped and oxygen supply to peripheral muscles recruited during exercise. 21,22 These adaptive alterations induced by exercise training include left ventricular hypertrophy to compensate for hemodynamic demand and interstitial fibrosis. 36,37 Within this context, increased interstitial collagen found in the ETI group may be an indicator of the physiological ventricular remodeling process, although no myocardial hypertrophy was observed. Indeed, some factors can restrict the accuracy of microscopic morphometry, such as tissue sectioning angle and the heterogeneous contractile state of cardiac fibers. 38 These factors may have contributed to the lack of detection of cardiac hypertrophy induced by exercise training. Intermittent fasting resulted in lower values of macro and microscopic morphology, which were not associated with changes of MAPK protein expression. The phenotypic changes induced by these peptides involve protein synthesis and cell growth, triggering hypertrophy and interstitial fibrosis, which may be associated with myocardial remodeling. 13,14 In addition, MAPK activation is also subordinated to the action of multiple growth factors, such as growth hormone and insulin, 24,33 whose secretion is regulated by nutritional behavior. However, it was not possible to verify association between intermittent fasting and changes in MAPK Table 2 – Nutritional characteristics and cardiac morphology Characteristics Group Factor (p-value) Control n=15 IF n=15 ET n=15 ETI n=15 Diet Exercise Interaction Nutritional variables FC (g/day) 23.30 ± 0.88 17.64 ± 1.00 * 22.88 ± 0.65 17.88 ± 0.77 ‡ <0.001 0.682 0.126 CI (kcal/day) 84.81 ± 3.20 64.20 ± 3.63 * 83.23 ± 2.38 65.10 ± 2.80 ‡ <0.001 0.665 0.121 TCI (kcal/day) 7124 ± 269 5393 ± 305 * 6980 ± 192 5468 ± 236 ‡ <0.001 0.602 0.100 FE (kcal/g) 0.023 ± 0.005 0.019 ± 0.004 * 0.020 ± 0.004 0.017 ± 0.005 0.005 0.050 0.581 BW (g) 395 ± 46 344 ± 37 * 374 ± 39 349 ± 30 <0.001 0.400 0.202 BWV (%) 71.0 ± 17.8 42.8 ± 12.0 * 60.5 ± 15.2 37.4 ± 13.6 ‡ <0.001 0.043 0.498 Adiposity (%) 2.11 ± 0.51 1.91 ± 0.77 1.89 ± 0.72 1.89 ± 0.79 0.584 0.508 0.578 Morphological variables AW (g) 0.059 ± 0.012 0.052 ± 0.009 0.066 ± 0.013 0.055 ± 0.015 ‡ 0.006 0.126 0.422 RVW (g) 0.134 ± 0.017 0.118 ± 0.034 0.145 ± 0.040 0.130 ± 0.020 0.055 0.143 0.950 LVW (g) 0.482 ± 0.066 0.404 ± 0.041 * 0.469 ± 0.060 0.436 ± 0.059 <0.001 0.509 0.138 AW/BW (mg/g) 0.152 ± 0.030 0.152 ± 0.026 0.177 ± 0.036 0.155 ± 0.048 0.247 0.136 0.227 RVW/BW (mg/g) 0.345 ± 0.033 0.346 ± 0.101 0.380 ± 0.076 0.368 ± 0.063 0.774 0.135 0.737 LVW/BW (mg/g) 1.24 ± 0.14 1.18 ± 0.10 1.24 ± 0.09 1.23 ± 0.14 0.202 0.437 0.457 AW/tibia (g/cm) 0.015 ± 0.003 0.013 ± 0.002 0.017 ± 0.003 0.014 ± 0.004 ‡ 0.007 0.227 0.328 RVW/tibia (g/cm) 0.034 ± 0.004 0.030 ± 0.009 0.036 ± 0.009 0.032 ± 0.004 0.065 0.246 0.982 LVW/tibia (g/cm) 0.121 ± 0.015 0.104 ± 0.009 * 0.117 ± 0.015 0.109 ± 0.015 <0.001 0.892 0.170 Heart weight (g) 0.674 ± 0.083 0.574 ± 0.063 * 0.680 ± 0.086 0.621 ± 0.058 ‡ <0.001 0.172 0.292 FC: daily food consumption; CI; daily calorie intake; TCI: total calorie intake; FE: feed efficiency; BW: body weight; BWV: body weight variation; AW: atrial weight; RVW: right ventricle weight; LVW: left ventricle weight;AW/BW: atrial-body weight ratio; RVW/BW: right ventricle-body weight ratio; LVW/BW: left ventricle-body weight ratio; AW/tibia: atrial weight-tibia length ratio; RVW/tibia: right ventricle weight-tibia length ratio; LVW/Tibia: left ventricle weight-tibia length ratio; * p<0.05 vs. Control; ‡ p<0.05 vs. ET (two-way ANOVA and Student-Newman-Keuls test). 189