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| Can fasted cardio switch on your "fat burning mode. And, more importantly, will it help you lose body fat faster? |
The study at hand, which was conducted by researchers from the Graduate School of Comprehensive Human Sciences at the University of Tsukuba can only inform us about the acute (24h) metabolic effects of cardio at different timepoints and with different amounts of food in the tummy (Iwayama. 2014).
High intensity interval training aka HIIT is more than just an alternative for steady state.
Never Train To Burn Calories!
Tabata = 14.2kcal /min ≠ Fat Loss
30s Intervals + 2:1 Work/Rec.
Making HIIT a Hit Part I/II
Making HIIT a Hit Part II/II
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60s of HIIT per week suffice!
- 100 min exercise before breakfast (AM),
- 100 min exercise after lunch (PM) or
- two sessions of 50 min exercise before breakfast and after lunch (AM/PM),
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| Figure 1: 24h fat and glucose oxidation during the two trials (fed condition) measured pretty reliably in a metabolic chamber (Iwayama. 2014) |
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| Figure 2: Relations of 24-h fat oxidation to average (r = -0.52, P < 0.01) and nadir (r = -0.72, P < 0.01) of relative energy balance were plotted on panel (left) and (right), respectively (Iwayama. 2014). |
Since the overall energy expenditure was identical in all trials, you should not be surprised that the increase in fatty acid oxidation in the AM group went hand in hand with a decrease in 24h glucose oxidation. A decrease of which the data in Figure 1 indicates that it largest in the AM (2062±96 kcal/24-h) trial, and hardly different for the PM (2374±114 kcal/24-h) compared to the AM/PM trial (2558±110 kcal/24-h), in which the fatty acid oxidation had been the lowest.
For people with type II diabetes interval training and thus burning more glucose than fat during the workout would be the preferred method. At high intensities you will burn a lot of fat after the workout, anyway (learn more). And even at low intensities, interval training is more effective than "steady state". Only recently, scientists from the University of Copenhagen have been able to show that at intensities that were as low as 40% VO2max during active rest and 70% VO2Max during the intervals, interval training is more beneficial than steady state cardio training with identical energetic costs (Karstoft. 2014).
Fat oxidation up, glucose oxidation down: At first sight, a 47% difference in fatty acid oxidation sounds like a huge advantage, but the fact that you oxidize fat, not carbohydrates does not necessarily mean that this fat (a) comes from your belly and other areas, where you may want to lose it, and (b) will not be restored after the workout.
In a caloric deficit, on the other hand, one could cautiously argue that burning more fat for fuel could lead to a slightly faster depletion of the adipose energy stores and thus slightly (not by 50%!) accelerate your weight loss. Plus: As long as you burn fat for fuel, your chances of running low on blood sugar and experiencing hunger pangs and cravings will be significantly reduced.
For the average physical culturist, there is yet another significant benefit: All the glucose / gylcogen you don't use during your cardio workouts will be available for your strength training sessions, where you will need them to lift heavy and thus promote lean mass retention | What are your experiences with "fasted cardio"? Comment on Facebook!
In a caloric deficit, on the other hand, one could cautiously argue that burning more fat for fuel could lead to a slightly faster depletion of the adipose energy stores and thus slightly (not by 50%!) accelerate your weight loss. Plus: As long as you burn fat for fuel, your chances of running low on blood sugar and experiencing hunger pangs and cravings will be significantly reduced.
For the average physical culturist, there is yet another significant benefit: All the glucose / gylcogen you don't use during your cardio workouts will be available for your strength training sessions, where you will need them to lift heavy and thus promote lean mass retention | What are your experiences with "fasted cardio"? Comment on Facebook!
- Iwayama, K. "Transient energy deficit induced by exercise increases 24-h fat oxidation in young trained men." Journal of Applied Physiology Published (2014). Ahead of print.
- Karstoft, Kristian, et al. "Mechanisms behind the superior effects of interval vs continuous training on glycaemic control in individuals with type 2 diabetes: a randomised controlled trial." Diabetologia 57.10 (2014): 2081-2093.