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This study discussed that it's not the rate of fat oxidation or the amount of fat oxidized that leads to better fat loss. The "fat-burning hypothesis" is starting to fail.
HIIT, which uses mostly glucose/glycogen as a fuel source leads to better fat loss than slow to moderate pace cardio.
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The study also discussed that consuming a meal further away from exercise, as to increase fat oxidation, leads to worse fat loss than when a meal is consumed right before or after training.
Most interestingly, they took swimmers from sea level and moved they to an altitude training camp at 2300 m above sea level to decrease oxygen availability and increase CO2.
"The fat-burning theory, referring to increased conversion of abdominal fat into carbon dioxide via oxidation during and after exercise, is not uniformly backed up by scientific evidence and such concept may lead to less effective recommendations for abdominal fat reduction regarding the type of exercise"
Another big reason for the superiority of HIIT and resistance training, is that it stimulates the production of new mitochondria to a greater extent than slow pace cardio, improves their quality and promotes greater metabolic flexibility.
HIIT, which uses mostly glucose/glycogen as a fuel source leads to better fat loss than slow to moderate pace cardio.
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"As exercise intensity increases from the sedentary state, the human body becomes increasingly anaerobic and more dependent on carbohydrates (particularly the glycogen stored in skeletal muscle) as a fuel, with a concomitant decrease in energy dependence from plasma fatty acid (produced mainly from adipose tissue) (Romijn et al. 1993) (Figs. 2A and 2B). The most important evidence against this “fat-burning hypothesis” comes from a study using indirect calorimetry in a respiration chamber. This study shows no difference in 24 h fatty acid oxidation between sedentary and exercise conditions (Melanson et al. 2002b). Furthermore, exercise does not increase 24 h fatty acid oxidation when energy balance is maintained (Melanson et al. 2009). Both aerobic endurance training and anaerobic weight training do not appear to increase 24 h fatty acid oxidation"
"However, a recent systemic review has concluded that low intensity exercise training is less effective in reducing body fat than moderate to high intensity exercise training (Tremblay et al. 1994; Vissers et al. 2013). ... Furthermore, 10-week HIIT (anaerobic in nature) decreases more total body fat and trunk fat than 40 min of continuous aerobic exercise at 60% VO2peak, when energy expenditure and weekly frequency are comparable (Trapp et al. 2008)."
"However, a recent systemic review has concluded that low intensity exercise training is less effective in reducing body fat than moderate to high intensity exercise training (Tremblay et al. 1994; Vissers et al. 2013). ... Furthermore, 10-week HIIT (anaerobic in nature) decreases more total body fat and trunk fat than 40 min of continuous aerobic exercise at 60% VO2peak, when energy expenditure and weekly frequency are comparable (Trapp et al. 2008)."
The study also discussed that consuming a meal further away from exercise, as to increase fat oxidation, leads to worse fat loss than when a meal is consumed right before or after training.
"Delaying meal supplementation after exercise attenuates increases in glycogen storage (Ivy et al. 1988) and glucose uptake in exercised leg (Levenhagen et al. 2001), which also leads to less effective fat decreases by exercise training (Suzuki et al. 1999; Trapp et al. 2008). Therefore, workout schedule in relation to meal time, particularly when circulatory hydrocarbon sources are surging before being partitioned to adipose tissues, would be crucial to maximize the negative balance of abdominal fat cells for triglyceride storage. This concept is supported by evidence from a randomized study in which weight-trained men consuming a meal immediately before and after training demonstrated a greater decrease in fat mass and an increase in lean body mass compared with consuming a meal in the early morning and late evening (Cribb and Hayes 2006). Similar to this human trial, delaying meals in animals for 4 h after exercise training results in greater fat accumulation and less muscle mass compared with animals receiving a meal immediately after exercise (Suzuki et al. 1999)"
So how is this possible then? The fuel is used for repair and creation of new cells instead of oxidation.
"In compliance with the second law of thermodynamics, exercise is a stress that increases the entropy of the cell, a highly ordered molecular aggregate. To bring a challenged cell or tissue back to a stable condition, damaged and energy-depleted muscle fibers will have to demand more postprandial hydrocarbon species compared with adipose tissues, leading to whole-body hydrocarbon source redistribution and resulting in a more favorable body composition"
"Some degraded hydrocarbon species may be recycled into challenged muscle tissues, where reconstruction is in high demand...Tissue growth is probably the most powerful magnet for hydrocarbon source settlement, which may cause a reciprocal size reduction of other tissues."
"Some degraded hydrocarbon species may be recycled into challenged muscle tissues, where reconstruction is in high demand...Tissue growth is probably the most powerful magnet for hydrocarbon source settlement, which may cause a reciprocal size reduction of other tissues."
Most interestingly, they took swimmers from sea level and moved they to an altitude training camp at 2300 m above sea level to decrease oxygen availability and increase CO2.
"In contrast to the sea-level counterparts (n = 8), body fat (measured by dual-energy X-ray absorptiometry (DEXA)) in all of the swimmers was unequivocally decreased and muscle mass was increased following altitude hypoxia exposure."
"Small decreases in blood oxygen saturation under such hypoxic conditions (97% versus 93%) resulted in an increased blood distribution to skeletal muscle (Chia et al. 2013). Because glucose and insulin are carried by blood, hypoxia would favor fuel deposition to muscle tissue versus adipose tissue"
And lastly,"Small decreases in blood oxygen saturation under such hypoxic conditions (97% versus 93%) resulted in an increased blood distribution to skeletal muscle (Chia et al. 2013). Because glucose and insulin are carried by blood, hypoxia would favor fuel deposition to muscle tissue versus adipose tissue"
"The fat-burning theory, referring to increased conversion of abdominal fat into carbon dioxide via oxidation during and after exercise, is not uniformly backed up by scientific evidence and such concept may lead to less effective recommendations for abdominal fat reduction regarding the type of exercise"