The body eats fat first. Muscle mass is typically converted to fat, then consumed by the body.
So long as you’re keeping active and supplementing yourself with the nutrients you need your body shouldn’t be going after your muscles until it absolutely has to.
It’s a survival mechanic because muscle powers us to escape predators, defend ourselves, and acquire food. Do we’ve evolved to burn up fat first in order to preserve muscle for other uses. Though there are circumstances that will make your body eat the muscles first.
*NOTE: I don’t know this case you’re referencing, nor am I nutritionist*
Fasting essentially throws your body into more of a ‘we don’t have calories available, let’s be smarter about using our fuel to not die’
Without eating (the preferred fuel of choice), the next source of fuel that the body will use is fatty tissue. Typically this will get used before moving on to the body’s proteins
Yes, your body *absolutely* works to preserve lean muscle mass. This is absolutely crucial, because some of your organs (like your heart) are composed of muscle.
When you fast, the first thing your body will use for energy is glucose (sugar). Since your body only stores small amounts of glucose, this will be used up quickly – within a few days. At that point, your body switches to *ketosis*, which means that it gets its energy from fat stores.
In fact, this is exactly why we store fat in the first place – to give our bodies a source of energy when we’re fasting. Periods for fasting were common in hunter-gatherer days, simply because we couldn’t always find food. If our bodies immediately switched to using protein, we would have gone extinct.
Fat is where extra energy is stored. The more fat you have, the more likely you’ll lose fat rapidly rather than muscle, as that’s what the body goes for first. The body tries to get rid of the problem (the excess fat that hurts it) rather than make another problem (consuming glycogen from liver and muscles) in most cases.
Preservation of lean mass is dependent primarily on energy expenditure and activity. Lean mass does degrade substantially through long duration fasting as the amino acids contained in the proteins of your body (in muscle, bone, convective tissues, really everything structural) are required for your energy systems to function when deprived of carbohydrates. It’s likely the guy who starved himself for a year lost a good 30-40% of muscle mass. This not my exact area within doctoral study, but its pretty close.
There are a lot of replies here, but nobody has actually answered the question. OP wasn’t asking about where his energy came from, they was asking how a specific person fasted for over a year and didn’t lose all of his muscle mass. Many amino acids (what is called “protein” on a nutritional label) are essential… which, by definition, cannot be produced by the body.
According to the wiki page, he consumed yeast, which supplied him with the essential amino acids that his body could use to maintain muscle mass:
https://en.m.wikipedia.org/wiki/Angus_Barbieri%27s_fast
Your body prioritises the breakdown of fat and conversion of it into energy as opposed to proteins of the muscles. Hence if a person is morbidly obese the fat would be metabolised as opposed the protein. Additionally carrying the weight of his morbidly obese self would have kept the muscles constantly under work and as such muscular atrophy would’ve been unlikely to occur
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