Fasted Cardio Before Breakfast Increases 24h Fat Oxidation by Almost 50% over Doing AM+PM Workouts, But This Does Not Necessarily Mean That You Will Lose 50% More Fat
|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).
In the experiment the nine young male endurance athletes, whose mean age was 23.2 ± 2.7 years of age (height: 168.4 ± 5.7 cm | weight: 59.5 ± 1.2 kg | body fat: 11.6 ± 0.6 %) and who had a relatively high cardiovascular fitness (O2max was 71.7 ± 6.4 ml/kg/min), performed three different types of exercise at different times in the day during a 42h stay in a metabolic chamber.
- 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),
|Figure 1: 24h fat and glucose oxidation during the two trials (fed condition) measured pretty reliably |
in a metabolic chamber (Iwayama. 2014)
|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.
- 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.