Simply put, cheese is a fermented concentrate of milk, and milk is rich in protein + calcium + healthy fats. A slice of full-fat Parmesan cheese has about the same amount of calories as a 100-gram can of yogurt.

The reason why it has a bad reputation of "making people fat" is that most foods with cheese are not healthy. At the same time, because they are relatively calorie-dense, it is easy to eat more and exceed the standard. If you are cooking at home, , add some cheese appropriately, it can not only provide healthy protein & calcium, but also not so easy to exceed the calories.
A slice of cheese sold in ordinary supermarkets is about 100 calories. Putting a slice in a sandwich will only make your sandwich more nutritious and delicious!

To sum up, eating cheese will not make you fat, just control the amount to about 25 grams per day.