My sister has a thyroid gland that isn't working like it is supposed to. A few years back she started putting on weight. At first we all thought she was just eating too much and needed to go on a diet. Most people start to put on a few extra pounds when they reach a certain age, so this is part of what we thought was happening.
Then the weight continued to come and she said she was eating less. This didn't make sense to us. We thought she was still eating too much, and we gave her a hard time about the weight gain and not exercising enough because it was a lot of weight and we wanted her to be healthy.
When she went to the doctor they did a special test and saw she had a thyroid condition. You would be surprised how much weight a person can gain in such a short time when there is a thyroid problem.