Mary's BMR is 1400 calories and she burns 900 calories in daily activity with regular exercise, walking around and doing household chores. To maintain her weight, she should be eating 2300 calories but, after keeping a food journal, Mary finds that she's eating 2550 calories every day. By eating 250 more calories than her body needs, Mary will gain one pound every 2 weeks.
that's exactly right, Mary will gain one pound every two weeks. that's 26 pounds a year, 260 pounds in ten years, and by eating this way for 40 years, Mary will have put on over one thousand pounds.
all Mary has to do is eat 500 fewer calories per day, so that in 40 years Mary can weigh around -1000 pounds.