Anyone who has ever lost weight was in a calorie deficit. It doesn't mean they had to count calories, but whatever they were doing they ended up eating less total calories than their body was burning. Every bodybuilder and fitness competitor and everyone else who has ever lost weight can attest that they had to eat less than they were previously eating to lose weight. You can achieve a deficit with low carb, low fat, keto, carnivore, vegan, fasting, whatever you like, in all cases the total amount of calories consumed has to be below maintenance for weight loss, and specifically fat loss, to happen.