Why you gain weight if you eat more than your cut

I answered someone in another topic and it was suggested to me that I give my response its own thread. It seems this is new information for a lot of people and it could potentially relieve a lot of anxiety about weight gain when increasing calories. So for anyone who thinks, "But 1700 calories IS my maintenance amount!" Or, "I must just have a really slow metabolism because when I go over 1200 I gain." ... this post is for you.

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The reason most people think they have to eat so little to maintain their weight is because our bodies naturally store glycogen and water in our muscles. This is the body's ready energy. When you eat at a caloric deficit, the glycogen stores (and the water molecules they must bind to in the cells) are shed first. That's why you get a big loss the first week of any diet. You just depleted your glycogen stores and now the body has no choice but to resort to fat in a continued caloric deficit.

So you keep up your deficit and your body is burning both glucose from the food you're eating and fat from your body (and some lean mass because you're in a deficit and that will just happen anyway) and you finally get to a weight you like. So you increase your calories to stop losing...

Or, you just decide to ditch the caloric deficit for a weekend of eating without discretion...

Or Christmas rolls around or you go on vacation and you eat to satisfaction and maybe a touch more...

... and you find you almost instantly put on 5 lbs.

All that has happened is your body has restored its glycogen stores and the water that glycogen must be stored with. In fact, trained endurance athletes will deliberately store extra glycogen by carb-loading before major events in order to have more energy for sustained effort. The body will, under perfect conditions, store this energy for use. It's part of being human.

So suppose you want to maintain your weight at 125 lbs. You diet down to 125 and then think, "Awesome! I will diligently increase my calories to maintenance." So you were eating 1700 calories/day to lose and you increase to 2000 calories daily... and after 1 week you've put on 1.5 lbs... so you cut back down to 1800 and your weight stays the same but now you're at 126.5... but you want to be 125lbs, so now you're just pissed off. So you go back down to 1500 calories for a week and you get back down to 125lbs. Then you increase by only 100 calories/day for a week and your weight stays the same... so you do it again... and you stay the same. You think, "Yay! I'm maintaining!"... And any time you eat over 1800 calories daily you start to gain again.

Why?

Because your body just wants 5 lbs of glycogen stores. The solution? Cut down to 5 lbs under your target weight and then eat at maintenance. Your body will rebound up to a healthy non-glycogen-depleted state and you'll be able to maintain relatively effortlessly and eat more food.

Okay, sorry... that was long-winded. I just cringe at the number of people who think they have to eat so little to maintain.

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So now having thought about my answer for another day or so, I do want to also say this:

1) I have no formal education in this field.
2) I believe how much glycogen is stored is relative to the amount of lean mass on a body. A 100lb person may store 2-3 lbs while a 250lb person could probably store up to 7-8lbs when combined with the water.
3) If your goal weight is unreasonably low because of ED, I am not recommending you cut to 5 lbs less than that

So with that said... feel free to discuss, rebuke, relax...