Is lowered T3 resulting from a low carb diet problematic? - PaleoHacks.com
You may find the response by Ambimorph to be interesting. It's the very long 2nd one. It's worthwhile to read the entire post. This is the conclusion he/she came to.
In conclusion, no, I do not consider it dishonest to minimize the observation that low carbohydrate diets can lower T3. Such lowering is protective of lean mass, and does not appear to be harmful or indicative of hypothyroid. It is completely reversible, which indicates that it is not causing an impairment of function, but rather is part of normal thyroid function. Finally, it may even be beneficial.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Highest squat: 167.5 x 2. Current Deadlift: 190 x 3