T4 vs T3
After my research on many sites i figured out the differnce here. The thyroid has 2 main hormones functioning from the TSH which is thyroid stimulating hormone. This TSH signals the body to release t4 and t3. It uses a feedback system so when TSH is low it says release more t3 and t4 and vice versa. One is the prohormone T4 which by itself is completly inactive. It simply can not do anything to the body in its t4 form. But what t4 does do is it is converted to t3. T3 levels affect catabolism of muscle, fat loss by acting on beta 2 receptors. TO MUCH T3 will be catabolic and breakdown muscle tissue by acting on the glucagon (storage of energy bonds) in the muscle. Therefore taking too high of a dose of t3 say 150mg plus is a way to lose muscle tissue more than fat. From what ive read t4 is known as synthroid and t3 cytomel. SUpplementing with t4 has no benifit for fat loss as it is inactive until converting with t3. Also when t4 converts to t3 as much as 20% is lose to the kidneys. SO it basicly is inefficient to take t4 for fat loss becuase it must be converted to act on the fat cells. T3 however is active and acts directly on the cells to speed epinephrine and norepihine (therefore causing increased Blood pressure and a fight or flight response) causing significant and effective fatloss.