The powers-that-be will be much more interested in the control of your thyroid disease. One of the common symptoms of hypothyroidism is weight gain, as I'm sure you know. Having said that, maintaining a healthy weight does help with control of the thyroid disease. A sensible, balanced diet, and regular exercise (30 minutes, 3 times a week) will help. Quite simply, if you use more calories than you take in, you must lose weight.
Get your thyroid function checked first, then talk to your doc about a sensible weight loss program. A dietician referral may help to assess your current level of intake, and to modify it accordingly.