So if you just sit there and simply eat less, the body will start to lower your metabolism to compensate for the missing calories. If you keep eating even less, the body will start to eat away at it's own proteins (muscle tissue and eventually internal organs) BEFORE it starts eating away at the fat.
This is killer, because the more muscle you have, the faster your metabolism is, and if you lose it, you're hurting your body's capacity to burn fat.
I've heard this umpteen times now from various sources. I say bullshit. If you consume fewer calories than you burn you will lose weight. Metabolic changes mean that there will be times when the weight stays the same but it will start up again. Frankly the idea of someone becoming a skeletal, organless husk before their fat arse disappears is risible.
Well yes the human body can only adapt so much, and it's not like it will eat ALL your muscle tissue before it touches the fat.
If you simply eat less without any exercise, the body will lower its metabolism very low, and will definitely burn fat, but it will also burn muscle, and this in turn will require you to eat less to keep in a calorie deficit, so it becomes progressively harder and harder to lose it. Once you get to your desired weight, it becomes harder to maintain it due to your body's low metabolism.
I'm sure there's scientific evidence I could dig up, but I don't need it, because I have ample empirical evidence, not only in my own body, but in friends I see at the gym and even my own family.
Back in 2004-2005, When I was lifting heavy weights, I was burning so many calories that I was eating 2 large pizzas a day just to maintain my bodyweight. People would think I was nuts and couldn't understand why I wasn't getting fat