Thyroid and weight loss problems

ATA Thyroid, BMR & Weight

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What is the relationship between thyroid 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). Indeed, measurement of the BMR was one of the earliest tests used to assess a patient’s thyroid status.

What is the relationship between BMR and weight?

Differences in BMRs are 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, such as amphetamines, animals often have a negative energy balance which leads to weight loss.

Hyperthyroidism

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Since the BMR in patients with hyperthyroidism (see Hyperthyroidism brochure) is elevated, many patients with an overactive thyroid do, indeed, experience some weight loss. Furthermore, the likelihood of weight loss occurring is related to the severity of the overactive thyroid. Thus, if the thyroid is extremely overactive, the individual’s BMR increases which leads to increased caloric requirements to maintain that weight.

Why do I gain weight when hyperthyroidism is treated?

Because the hyperthyroidism is an abnormal state, we can predict that any weight loss caused by the abnormal state would not be maintained when the abnormal state is reversed. This is indeed what we find. On the average, any weight lost during the hyperthyroid state is regained when the hyperthyroidism is treated. One consequence of this observation is that the use of thyroid hormone to treat obesity is not very useful. Once thyroid hormone treatment is stopped, any weight that is lost while on treatment will be regained after treatment is discontinued.

Hypothyroidism and Thyroid Hormone

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What is the relationship between hypothyroidism and weight gain?
Since the BMR in the patient with hypothyroidism (see Hypothyroidism brochure) is decreased, an underactive thyroid is generally associated with some weight gain. The weight gain is often greater in those individuals with more severe hypothyroidism. However, the decrease in BMR due to hypothyroidism is usually much less dramatic than the marked increase seen in hyperthyroidism, leading to more modest alterations in weight due to the underactive thyroid. The cause of the weight gain in hypothyroid individuals is also complex, and not always related to excess fat accumulation. Most of the extra weight gained in hypothyroid individuals is due to excess accumulation of salt and water. Massive weight gain is rarely associated with hypothyroidism. In general, 5-10 pounds of body weight may be attributable to the thyroid, depending on the severity of the hypothyroidism. Finally, if weight gain is the only symptom of hypothyroidism that is present, it is less likely that the weight gain is solely due to the thyroid.

How much weight can I expect to lose once the hypothyroidism is treated?

Since much of the weight gain in hypothyroidism is accumulation in salt and water, when the hypothyroidism is treated one can expect a small (usually less than 10% of body weight) weight loss. As in the treatment with hyperthyroidism, treatment of the abnormal state of hypothyroidism with thyroid hormone should result in a return of body weight to what it was before the hypothyroidism developed. Once hypothyroidism has been treated and thyroid hormone levels have returned to the normal range of thyroid hormone, the ability to gain or lose weight is the same as in individuals who do not have thyroid problems.

Can thyroid hormone be used to help me lose weight?

Thyroid hormones have been used as a weight loss tool in the past. Many studies have shown that excess thyroid hormone treatment can help produce more weight loss than can be achieved by dieting alone. However, once the excess thyroid hormone is stopped, the excess weight loss is usually regained. Furthermore, there may be significant negative consequences from the use of thyroid hormone to help with weight loss, such as the loss of muscle protein in addition to any loss of body fat. Pushing the thyroid hormone dose to cause thyroid hormone levels to be elevated is unlikely to significantly change weight and may result in other metabolic problems.

 

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