In 2010, researchers looked at a group of subjects who underwent 70 days of alternate daily fasting. That is, they ate one day and fasted the next. What happened to their muscle mass?
free mass started off at 52.0 kg and ended at 51.9 kg. In other words,
there was no loss of lean weight (bone, muscle etc.). There was,
however, a significant amount of fat lost. So, no, you are not ‘burning
muscle’, you are ‘burning fat’. This, of course, is only logical. After
all, why would your body store excess energy as fat, if it meant to burn
protein as soon as the chips were down? Protein is functional tissue
and has many purposes other than energy storage, whereas fat is
specialized for energy storage. Would it not make sense that you would
use fat for energy instead of protein? Why would we think Mother Nature
is some kind of crazy?
That is kind of like storing
firewood for heat. But as soon as you need heat, you chop up your sofa
and throw it into the fire. That is completely idiotic and that is not
the way our bodies are designed to work.
does the body retain lean tissue? This is likely related to the presence
of growth hormone. In an interesting paper, researchers fasted subjects
and then suppressed growth hormone with a drug to see what happened to
muscle breakdown. In this paper, they already acknowledge that “Whole
body protein decreases”. In other words, we have known for 50 years at
least, that muscle breakdown decreases substantially during fasting.
suppressing growth hormone during fasting, there is a 50% increase in
muscle break down. This is highly suggestive that growth hormone plays a
large role in maintenance of lean weight during fasting. The body
already has mechanisms in place during fasting to preserve lean mass and
to burn fat for fuel instead of protein.
The above is excerpted from a longer article. Read the whole thing here: Fasting and Muscle Mass.