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Weight Loss and Metabolism

The thyroid gland is considered to be one of the body’s main control systems of a persons’ metabolism. Therefore, when starting a weight loss program, it is of the upmost importance to periodically evaluate the thyroid function. The evaluation is commonly done by simple blood test that measure the level of the hormone that controls the thyroid gland function and may also measure the hormones directly produced by the thyroid. Standard testing done by a primary care physician during someone’s yearly screening only test thyroid stimulating hormone (TSH), this is the hormone that controls the function of the thyroid itself. In weight loss, the evaluation should be more in depth and include not only the TSH but also the two hormones directly generated by the thyroid gland. These two hormones are thyroxine (T4) and most importantly, triiodothyronine (T3).

T3 is the active form of the thyroid hormone in our body, it is responsible for all the actions of the thyroid that leads to an elevated metabolism. T4 is important but it is referred to as a prohormone, it circulates throughout the body and is converted to its active form, T3. Testing only for TSH may be an adequate screening tool for patients that have no symptoms related to low or high thyroid. However, TSH alone is not a complete and accurate reading of the exact level of thyroid function in the body.

A thorough study of the thyroid is extremely important to understand in the weight loss field, because it is vital to know not only if overall function is normal, but where in the “normal range” does the function fall. If the level is towards the lower end of the range, meaning slow metabolism, that will generally negatively impact an individual’s weight loss efforts. On the other hand, if the function falls towards the upper end of the range, these individuals tend to have an optimal metabolism and can lose quicker and easier.

Ninety percent of the hormone produced by the thyroid is T4 (the inactive form) and only ten percent is T3 (the active form). Throughout our body we have an enzyme called deiodinase, which is responsible for converting inactive T4 to its active form, T3. Interestingly, as we gain weight and increase the fat composition of our body, these fat cells produce a chemical that block deiodinase from activating T4 and lead to a decrease of available T3 (active thyroid hormone). In simple terms, this means that the more weight we gain, the slower we make our metabolism by decreasing the amount of available active thyroid hormone.

In our office, one of the primary screenings that we provide to our patients is checking a patients’ blood work before starting on our weight loss program to personalize each patients needed treatment. It has become very common to see that the T3 levels tend to fall within the lower one third of the normal range. So before starting any weight loss program, consult a physician and don’t forget to check your thyroid. If ignored it could mean the difference between reaching your weight loss goals or getting frustrated with your results and quitting in the process. If your levels do fall in the lower end of the spectrum, there are many things that can be done to optimize your metabolism and enhance your chances of achieving your goals.

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