I am 6 feet tall and 6 weeks ago I weightd 250 pounds. I have been on a low calorie, low fat dies for these 6 weeks. I lost down to 235 pounds in the first 3 weeks. Now I am stuck at 235. I eat from 1000-1500 calories per day. Low fat, approx. 10-15 %. I walk 1-2 miles every evening. What is going on here? Why am I not losing weight?