Has the patient also had Free T4 and Free T3 tested? Those are the actual thyroid hormones, whereas TSH is a pituitary hormone. If Free T4 and Free T3 have been tested, please post the results and their corresponding reference ranges so we can see the actual thyroid status.
The patient will need to be on replacement thyroid hormones; is this patient currently taking necessary replacement hormones? If so, what medication/dosage is the patient taking and how long have they been on the medication?
There is no specific diet for a patient such as you describe. It's recommended that those with hypothyroidism avoid cruciferous vegetables, such as broccoli, cauliflower and others close to the time of taking their medication. These are called goitrogens... It's important to note that cooking eliminates the goitrogenic properties of these foods and the benefits outweigh the drawbacks. It's also important that a minimum of 3-4 hours be maintained between thyroid medication and certain supplements, such as calcium, magnesium and other minerals/vitamins.