Fat is more calorie-dense (9kcal/g) than carbohydrate or protein (4kcal/g), but it's also extremely satiating - it's very difficult to overeat fat-dominant food

Fat is more calorie-dense (9kcal/g) than carbohydrate or protein (4kcal/g), but it's also extremely satiating - it's very difficult to overeat fat-dominant foods, particularly if you aren't eating it in tandem with sugar. Most of the foods we think of as "fattening" are packed with a combination of fat and carbohydrate. Fat's also necessary for hormone production, so I'd be pretty wary of any attempt to replace it with something synthetic. For example, it's easy to overeat McDonalds french fries (11g of fat - 99kcal, 31g of carbohydrate - 124kcal, and 3g protein - 12kcal) but it's significantly harder to overeat just beef patties (7g fat - 63kcal, 8g protein - 32kcal). If you ingested 1000 kcal of french fries (roughly 4 small fries) vs 1000 kcal of beef patties (roughly 11 patties), I'd be willing to bet that you'd be significantly more satiated with the beef.