After 30+ years of dieting and then regaining, I am certain I am insulin resistant. If I put my weight and details into a TDEE calculator, it says I need 2500ish calories a day to maintain, so that would be 1500 calories to lose 2 pounds a week. That just doesn't work out in practice though. If I eat over about 1200 calories, I put on weight. And that's low carb, mostly keto, so it's not like there's any water weight from carbs.
I have been low carb and doing 16:8 or longer since 2018, but I am still about 7 stone overweight. Any time I overeat, eat carbs or drink alcohol, my body puts on fat.
The ONLY way I can lose weight now is to not count calories, but eat keto/very low carb and fast for 36 hours three times a week. Despite not eating for 3 whole days, I still only lose about 1 pound a week. And I have to be consistent with it or I risk putting on again when I eat too much, drink or eat carbs.
I'm post menopausal, but I think the bigger problem is the insulin resistance. Books like Dr Robert Lustig's "Metabolical" and Dr Jason Fung's "Obesity Code" have helped me realise that I need to be consistent. I'm currently doing just that and have lost 16 pounds this year, so losing just over a pound a week.