I was diagnosed with Hashimoto’s hypothyroidism simultaneously with diabetes almost a year ago. I’m down 72.9 lbs. (Low carb, moderate protein for most of that time. BSD for 6 weeks (until my oncologists ordered me back to maintenance calories for 3 months during cancer treatment), and back on it again for the last 4 weeks.
I don’t notice a bit of difference losing weight this time than when I’ve lost weight on any other calorie limited diet.
As to testing for underactive thyroid, the most common test in the US is for TSH levels, which is an indirect test – at best. In order to properly adjust medications, you need to have your doctor test T4, T3, and rT3 levels. Synthetic T4 is the most common medication (levothyroxine). In a normal metabolism, T4 gets converted to T3 (a happy hormone, in my doctor’s lingo) – but if you have hypothyroidism, your metabolism isn’t normal – and often it mis-converts to rT3 (a sad hormone). So merely shoving T4 at the problem often fixes the TSH level (so you look properly adjusted) – but can’t tell anything about the important levels: T4 and T3.
I take 75 mcg of levothyroxine and 5 mcg of liothyronine (synthetic T3, to compensate for the fact that my body converts too much of the T4 into rT3)