Remember when Oprah blamed her weight gain and repeated failed attempts at weight loss on her thyroid? Well, she was partly right. The thyroid gland is a small organ with a big job. Located just below your Adam’s apple, the butterfly-shaped thyroid gland controls all your main bodily functions including your metabolic rate. It does this via two hormones, triiodothyronine (T3) and thyroxine (T4), which act on each organ in your body controlling the rate at which your body burns calories for energy.
By now you’ve probably guessed that there’s a relationship between your thyroid and your body weight. A deficiency of thyroid hormones (aka hypothyroidism) leads to a general slowing of metabolism, the rate at which the body burns calories from carbohydrate, protein and fat for at rest and at work. The speed of your metabolism is measured in terms of basal metabolic rate (BMR) which is the amount of energy the body uses at rest. Testing their BMR was one of the earliest methods of assess a person’s thyroid health. People with thyroid glands that were not producing enough T3 and T4 were found to have low BMRs, while those with overactive thyroid glands had high BMRs.
The cause of the weight gain in thyroid-insufficient individuals is complex – and not always due to excess body fat accumulation. In fact, most of the extra weight gained in people with hypothyroidism is actually caused by an accumulation of excess salt and water. Salt from a diet high in processed foods draws water towards it and water retention results. But fear not, massive weight gain is rare in hypothyroidism. Generally, only five to ten pounds can be blamed on lack of thyroid hormones. If more weight gain occurs, its likely due to other reasons.
Thyroid health also naturally affects total body health. Because of it’s role in fat metabolism, thyroid hormones levels tend to affect blood cholesterol levels. Normal thyroid hormone levels are thought to reduce risk of atherosclerosis (hardening of the arteries) while an imbalance can increase risk of heart disease, stroke and Alzheimer’s disease. Obesity is the common risk factor for these conditions and, as we discussed, weight gain is very common if you have hypothyroidism. It’s also more difficult to lose weight if your thyroid hormone levels are not balanced—but not impossible!
http://www.thyroid.org/patients/brochures/Thyroid_and_Weight.pdf (accessed October 5, 2010)