If you don’t eat, does your body eat your muscle or fat first?

As expected, this is also false. It shouldn’t be a surprise to anyone – it just doesn’t make sense. Off of the top of your head name some important muscles: heart, diaphragm, right? These are necessary to our life. Without them, we don’t function. Why would your body go and target these areas BEFORE going and eating away at fat? After all, stored fat has more energy than muscle (over twice as much, actually) and when was the last time you called someone “starving” because they had only fat and no muscle on them? That’s right, you didn’t.

So why do we continue insisting that our bodies are somehow programmed to preferentially break down our muscles over our energy rich fat? I think Alloran on Fitocracy made the best analogy – “Why tear apart chairs, tables, bed frames, etc. to build a fire when there’s a pile of firewood just outside the door?”

But I wouldn’t call myself Bill Nye with a vagina is I didn’t throw some science at you.

During a two day fast you have a 5 fold increase in Growth Hormone. Growth hormone is what tells the body to conserve protein and therefore muscles. More GH, more protein conservation. GH is a jack of all trades, though, because this badass chick also promotes lipolysis. For those of you who need a Latin reminder, lipo = fat lysis = killing or destroying.  GH kills fat and saves protein.  I told you she was a badass chick.

Growth Hormone isn’t the only big bad chick proving that you burn fat during fasting. Glycerol (released when the body breaks down stored fat) and palmitic acid (also found in fats) are high in the plasma during the first 12-72 hours of fasting. In fact, they double.

But if there’s so much science – and common sense – showing that you don’t lose muscle preferentially, where did it come from? Turns out a few studies showed a decrease in lean body mass (muscle) during a fast. Don’t worry, new science helped to remedy what may have been a misunderstanding. Turns out that majority of the “weight loss” from muscle was a loss of glycogen and water. Glycogen, for you non-bio nerds, is the stored form of glucose. So most of the loss of “mass” from muscle was water and stored glucose. Additionally, these same studies showed that about 14% of the energy from a fast came from protein, whereas 85% came from stored fat.

So no, skipping breakfast, participating in IF, or even lying on the couch all day not eating because you’re sick and lazy won’t cause your body to eat your muscles away. It just doesn’t make sense.

54 thoughts on “If you don’t eat, does your body eat your muscle or fat first?

  1. Chase Richardville

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    Reply
  2. Miguel d(^0^)b

    I know you mentioned it, but in my words. sitting and not eating will not make my musicale go away right? -_-

    Reply
  3. abigail

    You are stupid it burns muscle and fat that’s why u can loose definition and muscle mass withing 2 days of not eating

    Reply
    1. carrie

      Umm.. I don’t think you read the whole post Abigail… the point is you lose more fat than muscle if you just sit around. Calling people “stupid” is actually pretty stupid

      Reply
    2. Eddie

      The blog even states that the muscle mass lost is a form of glycogen and water and not the muscle itself. Did you even read it? I can vouch for this blog post since I’m a biology major and going to attend medical school.

      Reply
    1. Peter

      LOLOL Your Heart is a giant muscle, not sure if you’re trolling or you didn’t pay much attention in anatomy, if you don’t believe me look up (on google) Is the heart a muscle? and the diaphragm pulls down on your lungs only muscles pull and push, so common sense says it’s a muscle too, not sure if troll or just really stupid

      Reply
    2. Mohammad Mohammad

      Wow, you dumbass. Your heart is an organ, but it is classified as a MUSCULAR ORGAN. The diaphragm is a sheet of MUSCLE….dumbfuck. Leave the guy alone, this blog is great.

      Reply
  4. Petrova

    ^ Despite its classification as an organ, the heart is made up of a lot of muscle. Don’t be so quick to call people stupid or you end up looking stupid yourself.

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  17. Rich

    I hate to be a hater, but this author is so misinformed is laughable. Your body knows how to distinguish muscle and organs, it doesnt just classify it all together. Your ‘logic’ is illogical on so many levels, and anyone who works out can tell you that skipping a meal or two makes DRASTIC differences in your muscle retention. ATP is the most readily available form of energy and is most present in your muscles. Fat takes time and effort to convert into usable energy. You really shouldn’t blog bad information, its dangerously misleading to the common public

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  27. Alexandra

    My goodness are you amazing! Common sense wins again. Thanks for this posting. I’ve often wondered the same… We don’t NEED fat as much as we need muscles. If excess fat was created to be stored for later, why wouldn’t it be the very first thing to go!?
    Thanks again!

    Reply
  28. att

    Not sure if the logic connects here… No one says your body ONLY eats muscle. Of course it also eats fat, so the “when was the last time you called someone “starving” because they had only fat and no muscle on them?” comment isn’t very relevant because a starving person would break down all available sources of energy, both muscle AND fat. Also, the heart and diaphragm comments don’t work either. Your body knows those aren’t disposable, but it does eat your biceps and other muscles, so obviously you can’t use those as examples for your case. It seems like purposely framing the context in a way to support a point.
    Another thing: the question was if your body burns muscle or fat FIRST, and your answer was “false.” Wtf? Then you go on to support how your body won’t go for muscle, even though it will. Yes, fat has more energy. By that I think you mean 1g of fat has more calories than 1g of protein. But this doesn’t mean your body automatically goes for “energy rich fat.” You fail to mention that it takes more calories/energy to maintain muscle, so it would also make sense that your body would kill 2 birds with 1 stone by getting energy from muscles and also reducing the amount of energy it needs to maintain your overall muscle. A very muscular person would lose a lot more muscle than fat during fasting than a very fat person would. Muscular and fat people aside, according to the National Council on Strength and Fitness, or NCSF, those who fast or skip meals start to lose mainly lean muscle tissue.
    Your bit about the growth hormone is why people do IF for body building, but it doesn’t mean fasting doesn’t eat muscle. These body builders increase their HGH and then intake a lot of protein. If you’re straight fasting, HGH is pretty pointless because there’s no protein for it to synthesize.
    This is dragging on a bit so I’ll get to your last section. Your muscles’ main fuel is glucose, so if those are gone, then your body can’t maintain the muscle. Also, the 14% vs 85% thing is misleading. Like you said, fat has more energy, so it takes far less fat than muscle to provide energy. The way you presented the numbers would make it look like almost 6x as much fat was lost, but not even 3x as much fat was lost once you convert the calories to grams.
    In the end, there are parts that are true and parts that are misleading about this. If you’re going to fast, you should do IF so you can manipulate your body to burn fat and maintain muscle. If you’re just going to fast for a long time or you’re just skipping a bunch of meals, you will definitely lose a lot of muscle.

    Reply
  29. Katie

    This post is poorly written.

    [If you don’t eat, does your body eat your muscle or fat first? As expected, this is also false. It shouldn’t be a surprise to anyone – it just doesn’t make sense.]

    The first sentence in this post is what doesn’t make sense. You should have titled this “If you don’t eat, does your body eat your muscle first?” What you said was that it doesn’t make sense to think your body uses muscle or fat.

    Reply
  30. Isaac

    Love att’s comment. anyone who has a deeper understanding of biology than a what a high school education gives you would know that science is definately twisted in this blog for the authors purpose. the author takes her knowledge and then makes assumptions instead of the whole article being based off facts. people like this article because they want to believe it instead of looking for references and seeing if there is any truth. thats why this country is full of sheep. too many idiots being swayed with twisted truths and people just nod their heads as if to say “yeah.. that sounds right. lets go with that!”

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  32. Tropical bird

    Muscle takes more calories to maintain than fat does. If your food intake is nil or close to it and you are not exercising, your body will reckon it can lose some of the expensive muscle and should keep the fat. Basically, it thinks you are holed up in a cave somewhere, waiting for the big freeze to thaw.

    However, if you are working out, even on low calories, your body will reckon you need the muscle to find whatever food is out there, so it’s less likely to burn muscle and more likely to burn fat.

    As long as you are using your muscles, your body won’t burn it except as a last resort.

    Reply
  33. Renee

    Thank you! I have been working so hard to lose weight and have been told numerous times, the body eats muscle before fat. For the life of me I could not grasp that because if thats the case then why is it that people who don’t eat….or reduce intake lose and or are thin! Thank u again ur awesome this cleared up allot!

    Reply

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