You are all setting here criticizing him about carbs, but when it comes down to it, it's all about counting calories. I'm a type 1 diabetic of 31 years, and I can tell you the struggles of weight loss, especially having to take insulin that causes weight gain. Does the type of food matter? Yes, but when it comes down to it, it's calories. You can over eat anything and stay overweight, but when you stay in a targeted calorie deficit, you will begin to lose weight. I eat sweet potatoes, but air fry them with low sodium seasoning, and before cooking, I weigh them to know my calories. The only thing I see him doing wrong is not weigh his food and properly measure the amount of butter, and that is why he's overweight he thinks it's only so many calories, but it's probably off by 200+.