Excess calories are stored in the body as fat.
I think calories that are not part of an excess might be stored as fat. There are harmful substances that can be stored in fat. Omega 6 fats can be stored in fat. Plastic can be stored in fat. If you have too many toxins in your body, it might be a high priority for you to create fat so you can move toxins from your blood to the fat stores.
“I think calories that are not part of an excess might be stored as fat.”
Well that’s just it, if the body is truly in a calorie deficit, there isn’t any excess, by definition. If it somehow gets stored as fat, it’s comin right back out again for energy. Here’s why.
A certain number of calories are required just to “keep the lights on”. Just to keep your heart functioning, maintain temperature, etc. About 10% of the calories we take in are used up to actually digest our food too. I thought that was interesting. In Males this basal metabolic rate need might be 1600 to 1800 calories.
If the hypothetical male takes in 1000 calories, he is now down 600 calories for the day. Soon the glucose will be used up in the blood, muscles, and liver. In this scenario leave out any extra calories needed to offset exercise or work.
There won’t be any fat stored going forward, if he keeps that up. Any carbs in fhe meals eaten are immediately available for energy, but if we’re taking in 1000 cals, and our daily requirement is 1800 ... we’re coming up short anyway you slice it. This forces the body to turn to fat stores, and this is uncomfortable without practice. Most people don’t have practice. It’s just like a muscle that has become atrophied with disuse.
It most definitely isn’t linear, but if you figure out your personal metabolic rate, you can dial it in pretty close. Fats are 4000 calories a pound. Losing 1.5 to maybe 2.0 a week or so is sustainable over time. But for most people cutting back to 600 - 800 calories say, a more rapid weight loss diet, is pretty brutal at first.