Fasted Training vs Fed Training: Which will Burn More Fat?
Fasted training is an approach widely endorsed by many that claim it provides exponential health benefits such as a boost in metabolism, greater burning of “stubborn fat” and even claims to a degree that it increases growth hormone production. On the other hand, the counterargument for these claims, consist of something along the lines of “it will make you lose muscle” when in reality this claim isn’t fully correct.
If your considering fasted training for some of it’s so-called benefits listed above, then its important to understand its limitations on fat loss.
Firstly, it is important to understand the two states of satiety (the feeling of being full):
Fed Training: Otherwise known as postprandial – In this state, the food that you consume before training will be used by your body as fuel for the workout.
Fasted Training: Also known as post-absorptive – In this state, your body will revert to its own stores of energy as fuel for exercise.
From the above two pieces of information, it is easy to understand how many people can be misled into thinking that fasted training is more beneficial for fat loss.
More fat stores being used = More fat loss, right?
On the contrary, this is in fact reflected in the increase of fat oxidation (the process of breaking down fatty acids) not the rate of fat loss, the conversion of fat stores into usable energy by the body. However, the body is constantly in either a fed or fasted state, in which it is either storing energy or using energy.
If you are not eating, you must then be using fat stores, thus increasing the amount of fat burned (This also has links to intermittent fasting diets). This then leads to the rationale behind the statement that fasted training is more efficient at fat loss than training fed.
When all is said and done the overall individual calorie balance is what will determine/limit fat loss rates, if in a calorie surplus, the weight will be gained, if, in a calorie deficit, the weight will be lost.
The influence of fasted training on weight loss is non-existent, with no scientific evidence being reported or sufficient enough to support the claims of faster metabolism or increased growth hormone production rates.
Will I lose muscle training fasted?
On the other hand, staying in a post-absorptive state (fasted) for too long can influence heavier rates of muscle protein breakdown, resulting in the stigma that dictates fasted training is detrimental to muscle retention/building.
A loss of muscle over time will be the result of a negative balance between muscle protein synthesis and muscle protein breakdown – if you are consuming sufficient protein and are fuelled sufficiently prior to training, muscle loss will not occur.
But you can’t be fueled sufficiently before training if you’re fasting?
This statement is incorrect, the fuel used by the muscles while training is called glycogen, which is stored in the muscle cells as well as the liver. As an example, if you decide to begin your fasting period in the evening and are considering training in the morning, a high carb meal before the fasting period begins will sufficiently fill your muscle glycogen stores. These stores will not be depleted throughout the night as they are not required for performance. It takes a significant amount to largely deplete glycogen stores, even to the point where intense exercise has little effect.
A study conducted in 2013 looked at the effect of fed versus fasted resistance training during Ramadan in recreational Muslim bodybuilders. At the end of the study period, both groups maintained their training volume and did not report any changes in rates of perceived exertion (how difficult the session felt). The men in the study worked out between 4-6 pm, so they were fasted for about 15-16 hours before training and still managed to perform without any impairment.
In a study conducted by Tesch et al., nine subjects performed five sets of front squats, back squats, leg presses, and leg extensions to failure. After the exercise period had finished, the researchers took biopsies of the muscles and compared them with the biopsies pre-exercise, the results showed only a 26% depletion in muscle glycogen.
Conclusion and considerations
In conclusion, fasted training has minimal effect on the ability to reduce body fat and if done correctly, there is no evidence to suggest that there will be any detriment to muscle retention. Fasted training should be subjective to the individual and their lifestyle, if fasted training suits lifestyle and can provide a greater deal of enjoyment, without any detriment to performance then there will be no reason not to opt for this method. Some of my personal considerations for training fasted include:
- Consider a protein shake prior to training if possible.
- If the above is not possible, be sure to eat sufficient protein in your coming meals, preferably close to the peri-workout window.
- Stay well hydrated.
- Consider caffeine before training for energy.
Trabelsi, K., Stannard, S. R., Ghlissi, Z., Maughan, R. J., Kallel, C., Jamoussi, K., … Hakim, A. (2013). Effect of fed- versus fasted state resistance training during Ramadan on body composition and selected metabolic parameters in bodybuilders. Journal of the International Society of Sports Nutrition, 10(1).