Thyroid And Weight Treatment Service

Thyroid, Basal Metabolic Rate (BMR) and Weight

It has been appreciated for a very long time that there is a complex relationship between thyroid disease, body weight and metabolism. Thyroid hormone regulates metabolism in both animals and humans.

Metabolism is determined by measuring the amount of oxygen used by the body over a specific amount of time. If the measurement is made at rest, it is known as the basal metabolic rate (BMR). Measurement of the BMR was one of the earliest tests used to assess a patient’s thyroid status. Patients whose thyroid glands were not working were found to have low BMR, and those with overactive thyroid glands had high BMR.

Later studies linked these observations with measurements of thyroid hormone levels and showed that low thyroid hormone levels were associated with low BMR and high thyroid hormone levels were associated with high BMR. Most physicians no longer use BMR due to the complexity in doing the test and because the BMR is affected by many factors other than the thyroid state.

Differences in BMR is associated with changes in energy balance. Energy balance reflects the difference between the amount of calories one eats and the amount of calories the body uses.

If a high BMR is induced by the administration of drugs, people often have a negative energy balance which leads to weight loss. Based on such studies many people have concluded that changes in thyroid hormone levels, which lead to changes in BMR, should also cause changes in energy balance and similar changes in body weight.