The reason low-carb is good for a limited time is you're simply not combining a lot of fat and carbs in the same diet. Low-fat is sustainable longterm as proven by every successful civilization before the western diet started making it's way around developed nations.
If you're still having health problems and never tried a low-fat diet, I suggest you try it, but it has to be low enough in fat, yet high enough in calories. It's what has helped me the most.