What can cause low normal tsh, low normal t4 & low t3 (liothyronine)? Can intense exercise effect it? Can diet effect it?

Thyroid. Since your tsh and t4 are within normal limits, you probably have normal thyroid status. Exercise should not affect thyroid blood tests but excessive iodine or lack of it in the diet can affect thyroid status.An endocrinologist is best qualified to answer your question,however.