How fasting or changing the amount of food that you eat, tampers with your metabolism?
In: Biology
In general or body has three fuel sources: sugar, glycogen (a complex carb stored inside many cells in our body), and fat. (there is a fourth: protein, but our bodies will only start burning protein for energy if something is wrong or you are starving for a very long time)
When we eat a meal our blood sugar starts to go up. When our blood sugar gets high enough our body starts storing the excess as glycogen. But each cell can only store so much of that glycogen, so any left over sugar gets turned into fat and stored in fat cells, which are made to do that one thing, and fat cells can store an endless amount of fat. They’ll just keep packing it in and each individual fat can can become huge.
Our body really likes to hold onto the fat, it’s a fail safe for when food is scarce. You can imagine our hunter gatherer ancestors needed to be good at storing energy in case they failed to hunt or gather food that day. Or you can think about bears who get super fat before the go into hibernation. It’s all about energy storage.
When we burn energy we burn it in the same way: first the sugar in our blood, then the body will break down glycogen, then finally fat. When fasting in order to maintain energy levels, blood glucose levels, it will first start to break down glycogen to make those sugars. When glycogen stores run low the body then starts pulling from its emergency reserve: fat.
This is the purpose of intermittent fasting as a dieting technique. You’re forcing your body to burn through its glycogen stores and maximizing the amount of time your body is burning fat for energy. This is called ketosis, and is probably what you’re referring to when you say ‘metabolism’. Our bodies change they way they are metabolizing different stores of energy to ensure it has enough to function.
Edit: people keep commenting that my comment about intermittent fasting is wrong. It’s only wrong if you think intermittent fasting is just skipping breakfast. Many people who do intermittent fasting do OMAD, one meal a day, or implement 48-72 hour fasts to their intermittent fasting regime.
And in general, even by just skipping breakfast, you will be burning more fat during that period. Very rarely does the body do only one thing at a time. When you start fasting for any length of time you are going to be burning glycogen, metabolizing fat, and inducing gluconeogenesis (making sugar from fat and other sources). Fasting is a great way to burn extra fat stored in the liver (fatty liver disease, a precursor to type two diabetes and metabolic syndrome) b/c gluconeogenesis happens pretty much exclusively in the liver.
If you want to get more technical low blood sugar, like when you are fasting, will increase the amount of glucagon in your blood. Glucagon acts on peripheral tissues to tap into glycogen stores, on the liver to induce gluconeogenesis as well as burn glycogen, and on adipose tissue to induce lipolysis (break down of triglycerides into few fatty acids so they can be turned into energy in the liver). Even short periods of fasting will induce these actions. Will you go into full ketosis after a short fast? No. Will your body start the process after a few hours? Yes, even if it’s just a little at first. Metabolizing fat from peripheral tissues takes time, so the longer the fast the better.
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