I have read about people that say they cannot lose weight and I am sure some find it harder than others for no fault of their own. If you reduce calories down far enough, it is impossible not to lose weight. Check out people from concentration camps from the second world war in Germany and Poland or soldiers who were prisoners of war in Japan they were skeletal thin when released. OK a drastic example, but I reckon proves a point. Secondly, without a good supply of insulin, it is impossible to gain weight, no matter how much or what you eat. The photograph of the boy above was taken just around the time insulin became available for type one diabetics and he is skeletal. Within a few months this boy regained normal weight. So many times I have read type one's on forum's saying, I lost a lot of weight before I was diagnosed. Which leads me to think this.
The type two who is heavily over weight and has trouble losing weight is making lots of insulin still, which works in with Dr.Jason Fung's view, why give type two's insulin, it only makes things worse, sounds right to me. Also, many who say they can't lose weight, are not sticking to the plan, they talk constantly of falling off the wagon, or getting back to low carb tomorrow or next week etc. There are countless stories out on the internet of people losing weight, usually by calorie restriction, but the majority regain the weight, some more than they lost on the diet.
I have helped people, diabetics and non diabetics to drop calories to 1200 and maximum 30 carbs per day, the weight has fell off them. Some have stayed low carb and upped the calories to stabilise weight loss by way of fats and stayed low carb and kept weight stable, others have gone back to their old ways and back went the weight. This is not a quick fix it is a life long regime.
At the end of the day we are talking about control of insulin, whether natural or injected. Until that is achieved and stabilised, good control of BG and weight is not going to happen. Easier for some than others, but possible for almost all. One of the great myths re. a low carb high fat diet is you can eat as much as you like and you won't gain weight, complete nonsense, unless of course you are chronically low on insulin. That being said a calorie is not just a calorie. Eating 200 grams of fat has a totally different effect on the metabolism than eating the equivalent calories in highly refined carbs. Both from the insulin response and from the satiety perspective. The worst possible combination is a high fat meal combining a high amount of carbs.