Is it possible to lose weight with an underactive thyroid?

Hypothyroidism: First, your hypothyroidism must be treated. Then change your lifestyle to a healthier one. You don't need a drastic diet. Make small changes. Eat the right portions, eat 3-5 small meals a day, cut back on carbs and sugars, increase lean protein/veggie/fruit/water intake, and start doing some cardiovascular exercise. Continue to monitor your tsh, t3, (liothyronine) and T4 levels as well.