I was put on a low carb by my cardiologist 2 years ago (30g/day). I also run 3.5 miles/day. I have lost 70 pounds and have no negative effects. The positive effects include being off of all drugs and increased productivity and quality of life. I am not trying to argue the point, but it is important to not lump low carb with other diets. This is sustainable for the duration. My cardiologist’s opinion, not mine.