The classic “fat-burning hypothesis” is starting to fail; burn fat to lose fat…it doesn’t work that way…entirely.
Lots of people want to lose fat and they think cardio or some form of training that burns the most fat will result in the most fat loss. I have already debunked the fasted cardio myth if you want to check it out here: Myth: Fasted cardio for better fat loss. Busted!
Well this study (R) flies in the face of that and discusses how high intensity interval training (HIIT) leads to greater fat loss than slow pace cardio.
The interesting thing is that during HIIT your muscles utilize mostly glycogen; it oxidizes glucose and not fat.
So how can an exercise that that burns less fat lead to more fat loss?
It’s all about the second law of thermodynamics and nutrient partitioning.
Here’s what they say:
“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.”
What that means is that, the more you damage muscle cells with higher intensity work, the more nutrients are required for regeneration and cellular regrowth. This shuttles the nutrients that you eat to your muscles and not to your fat stores.
In line with this, studies show that eating 4+ hours before and after the workout leads to more fat gain than when eating right before or after the workout. This is because when you eat right after your workout, the carbohydrates are used to replenish glycogen stores and the fats and amino acids are used for cellular repair instead of storage.
This favorably redistributes nutrients (hydrocarbons) away from your fat stores and to your muscles. If you wait a few hours to eat after your workout, you lose this benefit.
But what about EPOC, that you get from HIIT?
Excess post-exercise oxygen consumption (EPOC, informally called afterburn) is a measurably increased rate of oxygen intake following strenuous activity. The afterburn effect burns more calories after training, without having to do anything.
“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 (Melanson et al. 2002a) (Fig. 2C). Nevertheless, both types of exercise regimens have been repeatedly demonstrated to decrease abdominal body fat at sufficient exercise intensity”.
That afterburn from HIIT is negligible and hardly worth mentioning.
But what I find most interesting is the effect of CO2 on fat loss.
Chia et al. did an experiment in 2003 where they took swimmers that were accustomed to sea level and moved them to an altitude training camp at 2300 m above sea level to decrease oxygen availability.
Here is what they found:
“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.”
Meaning, more CO2 production can help burn fat; shuttle hydrocarbons away from the adipose tissue to the muscles to be used for regeneration and oxidation.
This effect of increased CO2 can also be gotten from using an altitude mask (like this one) while training.
So there you have it, burning more fat does not mean losing more fat.
Now it’s not a great idea to go and do sprints daily, but rather twice a week and no more than thrice, depending on if you do other training as well. If you already do resistance training you’ll already reap this benefit and don’t need to do extra HIIT if you don’t want to. I do sprints because I like it and like to be functional and explosive.
Example sprint workout: (I like to do my sprints up a hill for more difficulty)
- 4 sets of 40m
- 3 sets of 50m
- 2 set of 100m
There is sprint training in my Ultimate Strength, Size and Skill Program where you build the ultimate androgenic physique with incredible strength and functionality.
Give that routine about eight weeks and watch your muscles explode! (In order to get the most out of your physique, get the complete six-month Ultimate Strength, Size and Skill program.)
Pre-workout to take so that you don’t puke if you’re unfit:
- 200mg caffeine (iHerb)(Amazon)
- 100mg vitamin B1 (iHerb)(Amazon)
- 5mg methylene blue (idealabsDC (product: oxidal))
- 1g HMB (iHerb)(Amazon) (if training semi-fast because of early training – it will help against muscle catabolism)
- A nice big fast digesting carb source like fruit or sugar 30 min before training if you haven’t eaten 3 hours before training.
HIIT is superior to other types of cardio for fat loss and it promotes fat loss by:
- boosting cellular regeneration
- creating new cells and mitochondria (mitochondrial biogenesis)
- increasing CO2 production
- increasing androgen production
- promoting uncoupling proteins and thermogenesis over time
Doing slow pace cardio is fine, but is not better. The more you do, the more your body down regulates its own energy expenditure (RMR, NEAT, etc.) to compensate for the increased energy expenditure from the cardio. Train smart.