How does burning calories for energy work? If someone runs on an empty stomach and burns 1500 calories, where did that energy come from? When they eventually eat something, how does the body know what to do with those calories?
In: Biology
Body has temporary stores of energy from previously consumed food. You have some very small stores of instant use energy in your muscles. The next step is glycogen stored in the body and bloodstream to supply longer needs. After that is your fat reserves.
Think of glycogen as your refrigerator, and fat as your freezer. You can eat your fridge food right away, but freezer food has to be defrosted.
Where food you consume goes is determined by hormones. Insulin is the master hormone that causes most of the direction. Consumed foods first refill depleted glycogen reserves. Then if that’s filled, body will convert and store as fat for later usage.
These systems are necessary because prior to civilization, the body never knew when it’s next meal was coming. So you would eat everything you could when you got a meal, and your body stores what’s not needed right away for later since it could be days or weeks before another meal.
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