This is what I have discovered from a certain amount of Internet foraging.
1. Carbohydrates (breakfast cereal, anything sugary) go straight to glucose which fuels the body, and in excess end up as body fat.
2. It's possible to live on a diet highly biased to lean meat + fat. The meat provides raw material for protein synthesis and the fat can synthesise glucose. This is the basis of the Atkins diet and similar.
3. Existing body fat will not be broken down to provide needed glucose until the blood glucose level first drops to a low value. Subjectively this will feel like being hungry. Don't be afraid.
An obvious conclusion is that starting the day with a generous bowl of cereal is a poor idea, whether the cereal is high or low in Glycemic Index. The resulting carbohydrate dump will convert to blood glucose, and only when that has been used up will body fat itself be raided.
Far better to have a meat + fat breakfast: ham and eggs; cheese, fish with a minimum of carbs via veg or fruit or bread.
A couple of days ago I dipped below 12 stone for the first time (from 13 stone 8 in August). Intermittent fasting (breakfast is allowed) several days per week seems to be working.