When it is overactive it makes too much thyroid hormone (thyrotoxicosis) it doesn't need. The cause of the hyperactivity of the thyroid gland need to be identified. Based on the cause and magnetude of the disease treatment plan should be worked out. Watchful waiting, medical therapy, surgical removal or radio iodine ablation are some of the steps. In rare cases, iodine excess or iodine related thyroid overactivity can be encountered. In this case low iodine intake and symptomatic therapy will be instituted.
When the thyroid gland is under-active (hypothyroidism) the thyroid gland makes less thyroid hormone. The exact cause should be identified as management plans are different. In America it is mostly due to autoimmune disorder. But in third world country it is due to nutritional deficiency of iodine. Treatment depends on the degree of the disease and the cause of the disease. Treatment could be from close monitoring to medical therapy.
When the thyroid is under-active the person can have the symptoms of weight gain, fatigue, irregular periods, depression, cold feeling, constipation etc. In most cases there is no diet that will fix overactive or under-active thyroid gland. In few case were iodine excess or iodine deficiency is the cause, controlling iodine intake will be advisable.
Generally eating healthy diet (good nutrition with sufficient micronutrients) regular exercise, maintaining ideal weight, avoiding stress and good sleep hygiene is very important. You can see a good nutritionist to guide you about micronutrients that supports thyroid health.
Your daughter may have under-active hypothyroid not overactive thyroid. Dot confuse high TSH with overactive thyroid gland. If TSH is high in most cases it means under-active hypothyroid (hypothyroid). That may be why your daughter is gaining more weight. If thyoid gland is overactive it mostly leads to weight loss than weight gain. Low carbohydrate diet will not fix the thyroid gland. It may be good to loss weight but not treat thyroid diseases.
Maintaining healthy weight, regular exercise and eating healthy diet will benefit not only the thyroid gland but also the overall body health.
Please discuss about these issues with your doctor. It is very important that you follow your doctor's advice.
I'd also advise going back to your physician and medical team to review whether you are talking about hypothyroidism or hyperthyroidism.
Stuart Brink, MD