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.
There is a lot of advertising and pseudoscience jargon out there right now concerning intermittent fasting since this the latest fad diet craze.
The science behind how it changes your metabolism and its effect on weight loss is not firmly well established, and do not let anyone tell you otherwise.
However, I am not saying intermittent fasting is ineffective.
It is like any other diet plan. There are many of them and the effectiveness of every diet plan depends firmly on your own personal behaviors.
The most important thing about picking any diet, is how easily you will be able to stick to it.
Whatever biological, metabolic, body changes or whatever differences between each diet is minuscule compared to your own behavior pattern.
If you find a fasting diet allows you to more control over your appetite and craving and it becomes easy and effective for you to stick to, then by all means do it.
If find another diet is easier for your lifestyle or behaviors or cravings then do that one.
Be honest with yourself and use your own sense and knowledge about body and behavior when dieting rather then trying to pick a diet based on whatever metabolic tricks any particular diets provide.
The body will respond to long spans of reduced food by basically reducing unimportant activity. A lot of this is sub-conscious reduction, (less fidgeting, leaning against a wall instead of standing freely, laying in bed a little longer, etc.). Over time, you might feel a little lazier too, where before you might be excited to do something, but now you’re maybe a little hesitant to do things. You may not even really notice.
The last peer-reviewed review i read on the subject reported little difference in efficacy when IF was compared to daily caloric energy restriction (a classic diet). Can link paper when i get home if people are interested. Basically the authors’ interpretation of the available data was that IF is good if it helps ypu eat less, but does little other than that.
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