There are many contexts for a calorie deficit, if you are too fat already, a calorie deficit is bringing you back to optimal.

In this context, it's important to recognize your body is an amazing homeostasis machine, it wants to stay at optimal.

If you don't eat processed foods, anything that comes in a box. If you eat a very low carb diet, such as carnivore or keto plant based diet. You're managing your insulin levels to normal, optimal ranges, which allows the entire body to operate its homeostasis magic. And even though you're in a calorie deficit, you don't feel hungry. Your body will want to maintain a calorie deficit, till it's back to normal.

The important key here, is to eat whole foods. Basically anything people ate before 1900, you can eat, and you will feel full with the right time, and you will be in a calorie deficit if you need to lose weight.

The big problem with processed food, sugar foods, the carb rich environment people find themselves in nowadays... These diets tend to spike glucose, maintain highly insulin levels all the time, reduce ghrelin production. Processed food specifically is designed to not satiate, to encourage continual hunger. Doritos are famous for engineering the perfect constant craving, through food science.

If you're always having elevated insulin levels, your body is always trying to be in an anabolic state, it's hard to burn fat. Your body only stores fat, all of your energy reserves are in fat. With a few exceptions in the muscles and a tiny amount of glycation in the liver. Since your body cannot meaningfully store sugar, or carbs, only the amount in the bloodstream remains, so you're always hungry because you're running out of energy.. I believe only 5 g of sugar can be in the bloodstream at any one time. You burn through that pretty quickly, in a hour or two, and hungry again.

In short, this is the food addiction cycle.

If you want to lose 1 lb in a month, or gain 1 lb, you need to consume or burn 3,500 calories. Or 116 calories a day. Or 38 calories per meal.... Easy right? .... In the US, calorie estimates are allowed to be off by as much as 25%, and that's just packaged food, forget any restaurant or line cook being exactly precise with portions... So for 2,500 average daily diet, over three meals, the margin of error is 208 calories. Your target is 38 calories. You're trying to do something within the margin of error of all of your estimates. Calorie counting is a very difficult game to do! The deck is stacked against you. This is why it's important to allow the homeostasis machinery in your body to handle all of this through satiation. It's going to do the right thing if you let it