Thyroid and Weight Loss: Cause or Effect?

Chapter summary

Many overweight people have symptoms that look like an underactive (hypothyroid) thyroid, especially after yo-yo dieting.
Science does not support the claim that the thyroid is the usual reason people cannot lose weight.
A sluggish thyroid is more likely the result of excess weight, not the cause.

The thyroid sits at the front of the throat and releases T4 and T3, which set the pace of metabolism. T3 is more active. Most T4 is converted to T3.
The hypothalamus signals the pituitary to release thyroid-stimulating hormone (TSH), which tells the thyroid to make more T4 and T3.
About one in 20 people has some thyroid dysfunction, and symptoms are easily misdiagnosed.
Hashimoto’s disease, an autoimmune condition, is a common cause of hypothyroidism.

Popular view: A sluggish thyroid explains weight gain and poor dieting results, and medication is the answer. Celebrities have promoted this.
The author’s view: Diet and weight loss may provide much of the solution for most people.
Why it is confusing: Lab tests often do not match symptoms, and normal-weight and underweight people also have hypothyroid-like symptoms or confirmed hypothyroidism.
Medical caution: Genuine hypothyroidism exists and needs diagnosis and treatment. Do not stop prescribed medication.

Small rises in TSH may signal an emerging leptin and insulin problem rather than thyroid failure. TSH returned to normal when weight was lost.
Leptin-driven weight gain appears to inflame the thyroid and trigger thyroid autoantibodies. These returned to normal after weight loss.
Radetti (2008, Italy): 137 overweight or obese children showed changes in thyroid structure and function, some without autoimmunity. Other factors must be involved.
Some people report that cutting out sugar resolved their thyroid condition, even Hashimoto’s. This is anecdotal.
Versini (2014): a review of 329 articles found obesity is a conclusive risk for rheumatoid arthritis, multiple sclerosis and psoriasis, and appears to contribute to thyroid autoimmunity.

Obesity appears to be a major environmental factor in autoimmune disease. If there is one message: reduce weight.
Blaming the thyroid is convenient, but excess weight is the more probable cause of a sluggish thyroid.

Versini, M., Jeandel, P-Y., Rosenthal, E. and Shoenfeld, Y. (2014) Obesity in autoimmune diseases: not a passive bystander. Autoimmunity Reviews. doi:10.1016/j.autrev.2014.07.001
Radetti, G. et al. (2008) Thyroid function and structure are affected in childhood obesity. J Clin Endocrinol Metab 93(12). doi:10.1210/jc.2008-0823
Richards, B. (2013) Leptin, thyroid, and weight loss. Wellness Resources.