During my most recent cholesterol blood work, I also checked my thyroid hormone levels in an effort to figure out why my cholesterol has gotten so high while I’ve been in nutritional ketosis.
One of the possible explanations was that:
Chronic low carb -> Hypothyroidism (low T3) -> Decreased expression of LDL receptors in the liver -> Higher serum cholesterol
Background – Here is an oversimplified explanation of thyroid physiology
- Thyroid Stimulating Hormone (TSH) – This is the hormone your brain sends out telling your thyroid gland to produce more thyroid hormone. If there is too little thyroid hormone, your brain will send out more TSH, and if there is too much thyroid hormone, it will release less TSH.
- Free T4 – This is the form of thyroid hormone sent out by the thyroid gland to regulate metabolism in the rest of the body.
- Free T3 – A more potent form of thyroid hormone. Tissues that receive T4 will convert it to T3 which is about 4x more potent than T4. The reason T4 is sent out instead of T3 by the thyroid gland is because T3 only has a half life of 2.5 days where has T4 has a half life of 6.5 days. One of the effects of T3 is: stimulates the breakdown of cholesterol and increases the number of LDL receptors, thereby increasing the rate of lipolysis.
- Reverse T3 (rT3) – Tissues that receive T4 can also convert it to rT3, an inactive form of T3. This occurs in certain conditions in which your body tries to conserve energy by slowing down metabolism such as fasting, low carbohydrate intake, physical or emotional stress, illnesses, surgery etc. Thus, under these conditions, not only will you have less overall T3 floating around, but rT3 can block T3 receptors so that the T3 you have left are even less effective.
Results From 3/11/13
- TSH: 4.350 uIU/mL (0.450 – 4.500) — 1.33 (11/16/12)
- Free T4: 1.09 ng/dL (0.82 – 1.77)
- Free T3: 2.1 pg/mL (2.0 – 4.4)
- rT3: 18.5 ng/dL (9.2 – 24.1)
A cursory glance shows that all my numbers are within the normal range meaning that my thyroid function is normal, but on closer examination, you see that my TSH is at the very upper limit of the normal range, and both my Free T4 and Free T3 are on the lower limit of the normal range (especially Free T3).
I also came across this insightful article by Dr. Sara Gottfried, supported by this report, stating that the revised normal range for TSH is 0.3 – 3.0 mIU/L. Using this new reference range, I would be considered hypothyroid. There’s also data out there showing that there really isn’t exactly a normal range for rT3, and that the most accurate way to interpret rT3 levels is as a ratio relative to how much Free T3 is available.
Since labs give results in all types of units, the folks at www.stopthethyroidmadness.com put together a handy dandy calculator that takes all that into account for you, where all you need to do is input your numbers and select the values, and it will automatically calculate your Free T3/rT3 ratio. A normal ratio, should be greater than 20.
My Free T3/rT3 ratio is 10.8.
What does all this mean?
Even though I didn’t have a full thyroid panel done in 11/2012, my TSH was 1.33, which is in the normal range under both the previous and new guidelines.
After three months of nutritional ketosis my TSH, free T3, and free T4 indicate that I’m hypothyroid, or at the very least subclinically hypothyroid (depending on which reference range is used). This is also supported by my low Free T3/rT3 ratio.
Over the course of this n=1 experiment I haven’t really noticed any symptoms of hypothyroidism:
- Fatigue – Only when I didn’t get enough sleep.
- Increased sensitivity to cold – Nope.
- Constipation – Nope.
- Dry skin – No dryer than normal.
- Unexplained weight gain – Maybe? This may explain my stalls in weightloss
- Puffy face – Nope.
- Hoarseness – Nope.
- Muscle weakness – Nope.
- Elevated blood cholesterol level – YES!!!!
- Muscle aches, tenderness and stiffness – Only after Crossfit and intense BJJ sessions.
- Pain, stiffness or swelling in your joints – Only when I don’t tap out in time during BJJ!
- Heavier than normal or irregular menstrual periods – I don’t have the parts to do this…
- Thinning hair – Not really, but I generally keep my hair short, so it would be hard to tell.
- Slowed heart rate – Resting heart rate is in the 50’s-60s.
- Depression – Nope.
- Impaired memory – Nope.
The entire reason I tested my thyroid levels was to explore possible explanations as to why my cholesterol is so high, and these results make me think that it truly has to do with my thyroid levels.
What is probably going on is the very low level of carbs I’m eating while being in nutritional ketosis is turning off my body’s production and utilization of thyroid hormone in order to preserve energy, and my high cholesterol is just a side effect of this.
Here’s a good article discussing this phenomenon. This also probably explains why my weight loss hasn’t really gone anywhere, since being hypothyroid slows down my metabolism making it harder to lose weight. Stay tuned for part 2 to see how I try to address these issues.
http://en.wikipedia.org/wiki/Triiodothyronine http://en.wikipedia.org/wiki/Thyroid_hormone http://en.wikipedia.org/wiki/Reverse_triiodothyronine http://www.stopthethyroidmadness.com/reverse-T3/ http://docbron.com/Thyroid_Resistance_RT3.php http://www.hormoneandlongevitycenter.com/thyroidtreatments1/ http://www.aafp.org/afp/2005/1015/p1517.html