Receiving a thyroid cancer diagnosis comes with a lot of emotions and fears. A big concern for most people is weight gain after their thyroid removal. 

There are lots of stories of thyroid cancer survivors struggling to control their weight.  I even like to say that I’m not really in control of my weight, my endocrinologist is.

I’ve heard survivors say, “I gained 40 lbs with no change to my diet after thyroid removal,” and “Weight loss is an uphill battle.”

But is that true?  Does everyone gain weight after their thyroid is removed?

This post will outline some reasons behind possible weight gain, the data on how often it happens, and what steps you can take to avoid it.

How is weight gain related to the thyroid?

Thyroid hormones have MANY functions in your body and can influence every cell in your body (1).  These include:

• Affect your basal metabolism, which is the basic calories your body burns to live (breathe, be awake, heart pump) outside of physical activity
• Regulate your heart rate
• Regulate body temperature
• Regulate bone health and muscle movement

There are three different thyroid hormones you need to know about.

1. Thyroid stimulating hormone (TSH) is made by the pituitary gland in the brain.  As its name suggests, this hormone stimulates the thyroid to make T3 and T4.
2. Triiodothyronine (T3) is the active form of thyroid hormone.  The thyroid makes less of this hormone than T4.  It stimulates receptors in cells to increase functions, such as increase heart rate, increase body temperature.
3. Thyroxine (T4) is the inactive form of thyroid hormone and lasts longer in your blood.  The thyroid makes more of this hormone than T3.  T4 converts to T3 inside the cells of the body. This conversion happens with or without a thyroid.

Measuring and Monitoring Thyroid Levels

The levels of your thyroid hormones – known as hypothyroidism or hyperthyroidism – indicate the effect on your metabolism. These levels are measured with your labs (blood tests).  

The blood tests will generally have the same name as the hormone they are measuring.  For T3 and T4, there are “total” tests and “free” tests, such as Total T4 and Free T4.  The “free” tests measure the levels of the hormone not bound to protein because these bound hormones aren’t usable by the body. (2) 

If you have thyroid cancer, your doctor may also monitor your thyroglobulin.  Thyroglobulin is a storage form of thyroid hormones only made by thyroid cells.  After total thyroidectomy and other treatment, it should stay the same or decrease.  An increase in thyroglobulin may mean there are still cancer cells in your body.  Always talk to your doctor about your labs.  (3)

Next, we will talk about what high or low levels of hormones mean.

Hypothyroidism

Hypothyroidism is when you have low levels of T3 and T4.  Because these hormones are low, you will have a high TSH, trying to get more T3 and T4 made.  

Hypothyroidism is generally associated with weight gain (4).  Other symptoms include:

• Fatigue
• Hair loss
• Feeling cold
• Constipation
• Loss of menstrual cycle in women
• Depression
• Brain fog or forgetfulness
• Muscle weakness or soreness.

Hyperthyroidism

Hyperthyroidism is when you have too much T3 and T4 in your body.  TSH levels will be low.

Hyperthyroidism is generally associated with weight loss (5).  Other symptoms include:

• Rapid heart beat
• Fatigue
• Difficulty sleeping
• Hair loss
• Increased appetite
• Tremor or shaking in your hands
• Sweating

When You May Experience Hypo- and Hyperthyroidism

Some people are diagnosed with thyroid cancer due to an abnormality in their thyroid labs. But many people diagnosed find a nodule in their neck but have normal labs.

After partial or total thyroid removal, you may experience some hypothyroidism while your dose is adjusted.  If you have a partial thyroidectomy, your thyroid may adjust and make enough hormones on it’s own without medication.  Your doctor may want to monitor you to see if that happens.  

If you have a total thyroidectomy, there is a science and art to getting your dosage right, so it may take awhile.  The science is there are loose guidelines of how much to give for your bodyweight.  However, each patient is unique, so it will take adjusting.

Prior to radioactive iodine treatment, doctors create a hypothyroid state in your body.  They do this by either stopping your oral thyroid medication or giving you thyrogen.  In both of these scenarios, your body makes more TSH, trying to stimulate any remaining thyroid (or cancer) cells.

For a few years after the removal of your thyroid, your doctor may keep you a bit hyperthyroid – give you more thyroid medication to keep your TSH level close to 0 (6).  This TSH suppression is to try and prevent the growth of any remaining cancer cells.  How low and how long your TSH is suppressed will depend on the stage of your cancer as well as your body’s response to other treatments – surgery, radiation, etc. 

Thyroid Hormone Replacement

There are different forms of thyroid hormone replacement.  I am not a pharmacist, so I will just give the basics of what different kinds are available.   For more information, see the American Thyroid Association.

T4 Replacement

The most common type of thyroid replacement patients receive is T4 replacement or levothyroxine.  The most common name brands are synthroid, Levo-T, levothyroxine sodium, levoxyl, novothrox, unithroid.

The dosing is not always completely interchangeable between brands, so doctors and pharmacists recommend you try to stick to 1 brand.  If you take “synthroid”, you will always get the same brand.  If you take “generic”, different pharmacies may carry different ones of the other 5 brands.  However, if you stick with 1 pharmacy, they generally try to stay with the same brand.

Tirosint is a name brand of levothyroxine with less dyes and fillers for people with allergies to those ingredients. 

T3 Replacement

T3 is a short acting hormone and made in smaller amounts in the body naturally by the thyroid.  Most patients do not receive long term T3 medication because of the possible side effects.

When taking T3, you have too high a level of T3 in your blood initially and then it rapidly decreases.  You can have rapid heart rate, insomnia, and anxiety.  It decreases so quickly that you often have to take it several times a day.  Because you cannot have steady levels of thyroid hormone in your bloodstream, it can be hard to manage and monitor this treatment. 

Cytomel is the brand name of synthetic T3.

Combination T3 and T4 Replacement

There are two types of combination replacement: synthetic and natural.

Synthetic combination replacement is not very common.  The pill is taken once a day and has much more T3 than would naturally be in the body, so it has the same side effects mentioned above. 

There is a growing interest in combination therapy by taking T3 and T4 pills at the same time.  There are trials ongoing in the effectiveness in patients who don’t achieve good results on T4 alone.

“Natural” thyroid replacement is made from dried and powdered animal thyroid glands.  NP Thyroid, Armour, and Nature Thyroid are the common names.  These contain both T3 and T4.  However, the ratio of T3 to T4 varies from animal to animal and differs from the ratio found in humans.  It will also contain fillers or binders, so it is not 100% natural.

Weight Changes Prior to Thyroid Removal

Going into cancer treatment, you may have had some weight changes.

Maybe you had Hashimoto’s or Grave’s disease.  Maybe you had symptoms of your thyroid not functioning properly and that is how you were diagnosed.

Weight gain or loss is possible prior to thyroid cancer diagnosis and treatment.  However, it is possible you had no issues.

Weight Changes During Treatment

There are several aspects to thyroid cancer treatment that can have an effect on your weight.

Mental Health

It is important to acknowledge that mental health plays a big role in how we eat, which can affect weight.  Also, life post cancer diagnosis is full of mental health pitfalls.

You may experience depression or anxiety from the time of your diagnosis on.  These symptoms alone can lead to weight loss and gain respectively.  If your mental health problems are severe enough for medication, those carry side effects of weight gain as well.  

Never discount the effect your mental health may have on your weight and overall well being.

Surgery

Surgery in and of itself is a major event for your body.  Often, people have sore throats after being intubated for surgery.  Their body also feels tired and weak.  They may lose weight as they are not able to prepare and eat much. 

On the flip side, if you are less active than normal as you recover, you could gain weight.  Also, your thyroid hormone replacement medication may not be adequate during this time, making you prone to weight gain.

Preparing for Radioactive Iodine Treatment

If you have to undergo radioactive iodine treatment (RAI), there are definite chances for weight changes. The most common effect I have seen for myself and in hearing from others is weight loss.  I’ll talk about all the reasons for either.

Raising TSH

Before RAI, your doctor will want to raise your TSH to well above normal levels to help the cancer cells absorb the RAI (7).  If this is done by stopping your thyroid medication, you will become severely hypothyroid. 

This may seem like it would make you gain weight.  However, you become so extremely hypothyroid that you feel unwell and often don’t want to eat much.  While you could gain weight, it is likely you could lose as well.  

Another option is to receive injections of Thyrogen prior to RAI and not withdraw from medication.  Thyrogen quickly raises your TSH, allowing the RAI to be absorbed without you being hypothyroid for several weeks. 

If you receive Thyrogen, the likelihood of weight changes related to your TSH levels is minimal.

Low Iodine Diet

The low iodine diet is also generally a cause of weight loss for people.  You follow the low iodine diet whether you are withdrawn from medication or receive Thyrogen.

Weight loss is common because the diet eliminates most processed foods and is very restrictive.  Patients eat healthier and/or less just because of the limited options, generally leading to weight loss.

Radioactive Iodine Treatment

During active radioactive iodine treatment, weight loss is still likely.

You will continue on the low iodine diet for several days after receiving the radioactive iodine.

The side effects of radiation may make you feel physically unwell.

You may have salivary gland inflammation, leading to extreme mouth dryness and taste changes, again, leading you to eat less.

While in isolation, your food options are limited to what you purchased ahead of time.

However, if you feel fine and eat to pass the time during your isolation, you may gain weight if you are severely hypothyroid.  

Weight Changes Beyond Active Treatment

Theoretically, you never “stop” being treated for your thyroid cancer, as you will likely be monitored for a long time and require hormone replacement.

However, as you go into your new normal life, it is important to be aware of how your thyroid levels can affect your weight.

Issues with hyperthyroidism

As I mentioned above, your TSH may be suppressed for a few years after treatment, leading to hyperthyroidism.  This could lead to weight loss.

However, it is important to not allow yourself to “abuse” your hyperthyroid state and use it as an excuse to eat anything you want.  That will lead to weight gain.  

During this time, it is extremely important to learn how to balance your intakes, as your levels will be more normal later and you don’t want to have to adjust then.

Issues with hypothyroidism

As I mentioned above, your thyroid blood levels will take time to adjust after surgery.  Especially if you went off thyroid medication for RAI, it will take awhile for your blood work to normalize after restarting medication.

It is also important to note that changes in blood levels cannot be fully seen for 6-8 weeks after a medication change.  So even dose changes can take awhile to take effect.

This time may be prone to weight gain.  So again, it is important to learn to eat healthy, balanced meals and snacks in proportion to your needs.

Aging

The peak age for papillary thyroid cancer diagnosis is 30-50 years old. (8) This age span is also when our metabolisms tend to slow and we tend to be less physically active.  Combined with thyroid issues, you could be prone to gain weight if you are not careful.  Many people without thyroid issues gain weight during this time frame.

So, is Weight Gain Inevitable?

This is a tricky question.  The research out there is not conclusive.  Anecdotal evidence from talking with thyroid cancer survivors will lead you to think it is inevitable.  

The tricky part of looking at the research is not that thyroid cancer patients do not gain weight.  It is whether or not they gain significantly more weight than normal thyroid patients.  Studies often do not find that difference.

What does that mean?

It possibly means thyroid cancer patients tend to gain weight as they age, as do most adults unfortunately.

Patients with total thyroid removal did gain more weight than others in one study, even though they had normal thyroid labs with medication. Postmenopausal women had the most weight gain. (9) 

How to Avoid Weight Gain After Thyroid Removal

There are several steps I would recommend to avoiding weight gain after thyroid removal.

• Take your medication as prescribed.  Take your medication every day, on an empty stomach, 30-60 minutes before eating.  Don’t take supplements within 4 hours.  By taking your medication regularly, you have the best chance of your labs being accurate.

• Find a doctor you like and who listens to you.  You will be seeing your endocrinologist on a regular basis.  Make sure you feel comfortable with him or her and can discuss any problems.

• Talk to your doctor about other options.  If you still don’t feel normal, talk to your doctor about measuring your T3 or other hormones.  Maybe you would benefit from supplemental T3.  Maybe another hormone or vitamin level is off in your body.

• Stay on top of your lab work.  If you start noticing a change in how you feel, talk to your doctor about checking labs.

• Recognize when other things are changing in your body.  Are you getting older?  More sedentary?  Are you going through menopause?  Other health issues?  Mental health changes?  Realize that your thyroid medication is not the only reason you may be gaining weight.

• Talk to your doctor at the first sign of weight gain.  Weight gain is always easiest to take care of when it is small.  Wouldn’t you rather lose 10 pounds than 50 pounds?  .

• Live a healthy lifestyle.  See my post on Diet After Thyroid Removal for more on this.

• See a registered dietitian.  Dietitians are THE nutrition experts and will have the best tools to help you with your diet. Many endocrinologists have dietitians as part of their practice.  Or find your own dietitian.  I have some listed on my resources page or look for one in your area at Academy of Nutrition and Dietetics.