Hi thanks for posting your query.I have gone through your details.According to my view weight gain or weight loss depends upon body BMR rate( basal metabolic rate).As you have mentioned that you are diagnosed with hyperthyroid.One of the main symptom of hyperthyroid is weight loss along with other symptoms like tiredness,sweating,fast heart beat,altered mood,frequent bowel movements.So in order to gain weight firstly you have to keep your thyroid level within normal range by taking medications,eating proper diet and lifestyle changes and secondly keep your metabolism proper as it is a metabolic disease. Diet Remedies for hyperthyroid and weight gain.. Consume more alkaline food like green vegetables,fresh fruits,salads and less acidic food. Have 4-5 small meals a day Have food which increases immunity in the body like wheatgrass,gooseberry,aloe vera. Have chyavanprash daily in the morning. Have 1 tbsp shatavari and 1 tbsp ashwagandha with lukewarm milk daily. have lots of cabbage,kale,brocolli to reduce over activity of thyroid gland. Fruits such as pears,peaches can prevent worsening of thyroid. Avoid alcohol,caffeine,nicotine as it can aggravate the problem. Take food rich in iodine along with protein supplements. Have banana with a glass of milk.Banana is rich in potassium and alkaline in nature. Soak few almonds ,dates,raisins overnight and have in the morning Herbal medicines to treat hyperthyroid Kanchnaar guggul,punarnavadi churn,ashwagandha,shatavari,bala,arogyavardhini,guduchi,sutshekhar ras . Practise yoga as an as and pranayam like sarvangasan,halasan,shavasan,yoga nidra,bhujangasan,ujjayi pranayam,anulom vilom,sheetali,sheetkari bhramri,meditation. Follow panchkarma procedures like Shirodhara( pouring of herbal oil over forehead) Body massage with medicated oils and herbs like bala,atibala. Niruha and anuvasan Vasti( for eliminating excess toxins and purification) Follow these remedies and I am pretty sure you will benefit from these. Hope your all doubts are clear. Wish you good health! Regards Dr.Pallavi