Is Your Thyroid Making You Fat?

Review of the book Is Your Thyroid Making You Fat by Sanford Siegal

Dr. Siegal is a D.O./M.D. who has been treating only overweight patients for 30 years. Some of his patients had great difficulty losing weight even with a low calorie diet, and he suspected hypothyroidism, yet when he tested their thyroid function it was normal. He solved that dilemma by the simple expedient of re-defining hypothyroidism as the inability to lose weight with calorie restriction.  In this book, he describes his process of discovery, his diagnostic criteria, his methods, and impressive anecdotal reports of success.

He assesses hypothyroidism in three ways:

1) Patients count calories for 28 days. They aim for 1000 calories a day, but if they exceed this, they simply count the extra calories. After 28 days, the weight lost, the caloric maintenance level (based on age, sex and activity level) and the number of calories consumed goes into a formula to calculate the metabolic function index. An MFI of 80 percent in a female who must eat 400 calories less than another female to maintain the same weight indicates hypothyroidism.

2) Basal body temperatures are taken on awakening. If the average is one degree lower than 98.6, it is suspicious, and a difference of 2 or 3 degrees definitely points towards hypothyroidism.

3) Symptoms of hypothyroidism are assessed. These include anemia, brittle nails, cold intolerance, constipation, deafness, depression, diminished sweating, dry or coarse hair, dry skin, fatigue, hair loss, headaches, hoarse voice, impotence, infertility, irritability, memory loss, menstrual pain and other abnormalities, miscarriages, muscle pain or cramps, numbness, overweight, palpitations, puffy facial features, sleeping excessively, slow movement, slow pulse, weakness, and weight increase.  Dr. Siegal developed a weighted scale with varying numbers of points for different symptoms, and added points for a slow Achilles tendon reflex. He made no attempt to validate the scale.

He estimates that up to 40% of the American population has undiagnosed hypothyroidism.  If he decides a patient is hypothyroid by his definition, even if the TSH (thyroid stimulating hormone) is well within the normal limits, he prescribes thyroid hormone, and adjusts the dosage based on the amount of weight lost. He only uses natural thyroid (desiccated thyroid USP), because in his experience it works better than synthetic levothyroxine (T4) and causes fewer side effects.  He starts with ½ grain (few physicians use this outdated measure any more; mg measurements are preferred) and gradually raises the dose until the patient is losing weight at an acceptable rate.

He has essentially declared a normal state to be a disease. He has invented his own diagnostic criteria and his own definition of hypothyroidism, without any attempt at validation. Subclinical hypothyroidism is an accepted medical diagnosis for mildly abnormal blood tests in the absence of significant symptoms or clinical findings; if not treated, this may progress to overt symptomatic hypothyroidism. Dr. Siegal’s diagnosis is just the opposite: normal blood tests with supposedly hypothyroid symptoms.

It is generally understood that giving thyroid to a person with normal thyroid function will cause a temporary hyperthyroid state and then the body will decrease its own thyroid production to compensate; after a short adjustment period the total hormone level will be back down to its original level.  Dr. Siegal does not do follow-up thyroid blood tests during treatment, so there is no way of knowing whether the hormone levels have actually changed.

A review of the literature suggests that there may be a subpopulation of hypothyroid patients who respond better to a mixture of (synthetic) T3 and T4, but there is no evidence that natural thyroid is better than synthetic, and desiccated thyroid fell into disfavor years ago because the dosage was not as consistent as with the synthetic preparations. Dr. Siegal claims that none of his patients have side effects from the thyroid medication; however, most physicians believe that thyroid is not indicated for weight loss and would not be effective unless it made the patient hyperthyroid, with the accompanying symptoms. A hyperthyroid state can cause arrhythmias and other serious consequences, and it is considered dangerous.

There are many potential sources of error in Dr. Siegal’s method: patients’ reports of calorie intake could be inaccurate; activity level and maintenance calorie requirements are estimates that could be way off; basal body temperatures for determining ovulation generally show readings well below 98.6 in normal women; it is unlikely that the American population has 40% undiagnosed anything; overweight patients desperately want a magic pill, so there should be a strong placebo effect; the doctor believes strongly in what he is doing and uses suggestion on patients; and the list of hypothyroid symptoms is poorly defined, subjective, and includes enough symptoms that it could apply to a lot of healthy people. Many of these possible errors could be ruled out by controlled double-blind studies.  He has never attempted to do one.

There may be a grain of truth in what he says, but there is also a strong probability that he has allowed himself to be fooled. All the hallmarks of pseudoscience are there: the one-size-fits-all (or at least 40%) diagnosis, the criticism of conventional medicine, the reports of universal success without documentation of numbers, the claim that his method is safe and without side effects, the dramatic anecdotal case reports, the lack of confirmation by other sources, etc.  Only good experimental evidence can determine whether his method is really safe and effective.

Before accurate blood tests were available for thyroid disease, hypothyroidism was a “fad” diagnosis, and was blamed for many ills, particularly obesity. When better blood tests became available, there was no longer an excuse to try thyroid treatment empirically. Dr. Siegal has created a new excuse. He says he is a successful weight loss physician, but he doesn’t present objective evidence of such success and his theory and methods are not based on good science.

This article was originally published in the Scientific Review of Alternative Medicine.



Dr. Hall is a contributing editor to both Skeptic magazine and the Skeptical Inquirer. She is a weekly contributor to the Science-Based Medicine Blog and is one of its editors. She has also contributed to Quackwatch and to a number of other respected journals and publications. She is the author of Women Aren’t Supposed to Fly: The Memoirs of a Female Flight Surgeon and co-author of the textbook, Consumer Health: A Guide to Intelligent Decisions.

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