I was told that you break down muscle fibers with resistance training and build the muscles back when you sleep (provided you have enough protein). What about fat burning? Do you burn fat while you work out? Sleep? I understand you lose weight when there is a calorie deficit but when does it actually happen?
In: Biology
None of that is true except for the fact that you lose weight when in a calorie deficit.
Your body processes are functioning all the time. There’s no magic time when your body decides to burn fat. If your body runs out of stored glucose it will convert some fat to glucose and use that. You could be sitting on the couch when it happens.
The same thing with muscle tissue. It may be more likely to happen after a meal when the levels of amino acids and insulin in the body are high, but again, it could also happen while you’re sitting on the couch.
you call it burning but it is actually breathing, the burning of fat, carbs or protein happens when you put those fuels to use with oxygen and whichever metabolic process occurs turns that substrate into CO2 and water
You burn fat when you are expending energy after you run out of easy stores of energy, like daily caloric intake.
Your body spends more calories keeping you warm than it does moving or thinking, or anything else, keeping you warm is the main thing that burns calories, so things like swimming, or walking or hiking in colder weather will be some of the best fat burning exercise.
So in reality the fat burning starts when your body burns past its daily intake.
Your fat is being continually “burned” – the stored chemical energy being converted into usable physical energy to move your muscles. This process happens at various rates depending on your body’s current activity level, but it is never completely off.
The main waste products are CO2 and H2O. So a large part of the loss goes to wherever your water goes (sweat, urine, etc) – and another large part goes to breathing.
Every time you flex a muscle, it tears a little.
Your body is constantly working to repair that damage. The more than muscle tears (through more use or more intense use) the body tries to build it back stronger. It doesn’t necessarily just happen during sleep. It does continue to happen during rest, but it doesn’t only happen during sleep.
Your body constantly needs a supply of glucose to keep operating. Normally, it gets that from breaking down carbohydrates you ate, but when there are extra carbohydrates, that glucose can be stored as fat. If there isn’t a supply of carbohydrates being digested, the body has to switch to start breaking down that stored fat to power your body. It’s basically a process that slows down when you have food that’s being digested, and speeds up again when you’re nearly done digesting the food.
Do not starve yourself to achieve this, that is dangerous. Simply eat less, particularly fewer carbohydrates. Drinks with lots of sugar are particularly bad for that. Sport drinks should be used to keep your energy up for long periods of exercise or activity where you need that energy, not for when you want to burn fat.
You can only use glucose as a power source. When none is available, you use glucagon, which is a starchy polymer of sugars. Fat is basically carbs that have been converted into a more stable form of energy storage. When you need it, your body turns fat into glucose in a process called gluconeogenesis. This produces ketones as a byproduct, which is why some people follow the “keto diet”. Ketones aren’t very good for your brain, by the way, so be careful if you attempt keto.
When you breathe.
Every moment of the day you have constant metabolism of tissues and storage of tissues.
CO2 is generated from using those stores of fat for energy.
So you have to breathe it off.
This is a very very Eli5 response. I have a bachelor’s in exercise physiology and doctorate in physical therapy.
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