 Needing too little for too long, you're going to get a slower metabolism. There's a range of calories that your body can burn with the same lean body mass that you have. Your body can learn to be more or less efficient with calorie storage, calorie burning, and just getting your body to think it needs to lose muscle. Even before it loses muscle, you'll start to see metabolic adaptation. Now if you lose muscle, now you've lost physical capacity to burn calories. And a slower metabolism makes it much harder in a modern society where you're surrounded by food and so on. Like it snapped my fingers and increase everybody's metabolism. Right now listening to this by 50%, everybody would lose weight, everybody would get leaner as a result. You don't want a slower metabolism unless you're living in the wilderness and you're hunting and foraging for your own food, in which case a slow metabolism is a beneficial. But if you live anywhere in any kind of modern society, a slow metabolism is not an asset, it's a liability.