Alright, this is a controversial one. Anything Paleo-orientated generally is. But let’s wade in. I have a number of reasons for distancing myself from the Paleo movement. I agree with many of the dietary principles inherent, just not the faddishness, the fanaticism and the insistence on basing it on a meta-theory of how we ate 10,000 years ago. I’m also cautious about the whole low/no-carb fervour in general. It’s not for everyone.
Like, for instance, anyone trying to get pregnant. But today I want to raise this one: cutting carbs might just trigger thyroid problems. Strap in. I recently came across American biochemistry and genetics expert, Dr. Cate, and have asked her to flesh things out…
People who run into trouble going low-carb seem to follow a pattern. First, they (make) a relatively abrupt switch to low carb (often less than 50 gm). Initially they lose weight as hoped but then, instead of feeling more energetic from their weight loss, they develop fatigue, sometimes accompanied by symptoms of low thyroid function including cold extremities, hair loss, and digestive problems.
Because their fatigue and other symptoms are classic for thyroid malfunction, many will get their levels tested, only to come away confused when the tests health practitioners typically order (TSH and T4) come out normal.
Those who get more extensive testing may get a test called reverse T3, or rT3 for short. These are often abnormally high, leaving them to believe they have found the root of the problem. Some are given a prescription for T3 (or thyroxin) in hopes of regaining energy and the intervention seems to help, at least a little.
Reverse T3 is a kind of chemical opposite of regular T3, a mirror image compound called an enantiomer. Reverse T3 has opposite effects of T3, and has long been associated with a set of symptoms aptly called hibernation syndrome—fatigue, weight gain, and so on. If you have suffered from severe hypothyroidism, you may have gone through times where you felt like you really just want to crawl away to a quiet place and rest for a long, long while. Your body was telling you to hibernate.
Why low carbing triggers thyroid drama
In doing research on rT3, I ran into a fascinating article on a group of little-understood compounds called thyronamines (pronounced thigh-row-na-meens). The key to understanding rT3, and unlocking the relationship between carbohydrate consumption and thyroid function, may lie in these newly discovered compounds.
Thyronamines have powerful effects on energy metabolism. Studies performed in 2010 showed that injecting thryronamines into the belly cavity or brain tissues of experimental animals cause the following physiologic and behavior changes:
- Impaired ability to utilize sugar as an energy source
- Insulin resistance
- Lowered basal body temperature
- Weaker than normal heart contractions
- A marked decline in activity (We can’t ask the lab animals, but presumably this would be induced by what we would describe as feelings of extreme fatigue)
Upon injection, the effects begin within minutes and last 8-12 hours.
And here’s the punchline: Thyronamines appear to be manufactured from that go-to-sleep hormone reverse T3. We can’t yet test you for high levels of thyronamines, but in testing your rT3, we are testing for the precursor of thyronamines. And I expect that, when studies are done in people, we will discover that high blood levels of rT3 does indeed correlate with high tissue levels of thyronamines.
I think this research is vitally important and that we will be hearing more about thyronamines in the future. But we are still left with a very important question that remains unanswered: What do we do about it?
Let’s explain it with The Bear theory
Bears are omnivores, just like humans. And, of course, bears hibernate. Understanding the variations of a bear’s diet throughout the year helps us to understand why biology has built into our mammalian metabolism a sensitivity to changes in carbohydrate consumption.
Imagine you are a bear living in Yellowstone National Park. It’s late summer and the salmon runs are gone, the grazing animals born in spring have now grown too fast for you to catch, the grubs under the rocks are all hatched, and pretty much all that’s left, aside from campground garbage, is nuts and berries. Plucking ripe berries off a bounteous shrub is far easier than cracking nuts, so you gorge on berries. In a few weeks, though, the berries are gone and there’s very little food left. That’s okay, because the abrupt decline in carbohydrate consumption is accompanied by increased reverse T3 and increased production of thyronamines, which makes you feel exhausted. Thanks to all the weight you gained, you are now so well padded with cushy fat that you think you could just crawl into a cave somewhere and sleep for a long, long time.
Research in humans shows that, just like bears, our thyroid hormones are influenced by major changes in the amount of carbohydrate consumed.
The real problem? Doing it too fast
The bear in the woods theory suggests that it is the relatively sudden change from high carb to low that flips the switch. For some, an abrupt decline in available glucose may trigger an atavistic hibernation reflex, which will trigger the conversion of a thyroid hormone called T4 into something other than the normal T3, namely into the reverse form, rT3. rT3 then gets converted into thyronamines and causes all the symptoms of low thyroid function without significant deficiencies of thyroid hormone showing up on lab tests, leaving people to worry there is something incredibly wrong with their hormonal function.
If you have gone low carb successfully, you have accomplished a major change in your metabolism, one that involves turning on scores of enzymes your body has not needed or used for a long time, decades in some cases. Not everyone can accomplish this overhaul in time. Those who can often continue low carb for life with great success. But those who cannot accomplish all the necessary changes flip the hibernation switch, increase production of rT3 and thyronamines, which causes crushing fatigue and may lead to intense carb cravings in order to turn off the hibernation switch again.
For these people, an easy way to avoid flipping the hibernation switch and reduce carb cravings may be to simply make a more gradual reduction in carbs rather than an abrupt one. Atkins, who advocates an abrupt switch to less than 20 gm per day, seems to have been aware of this problem and in fact in his writing he warns people they may experience fatigue in the first few days or weeks after going very low carb. Unfortunately, for some people, the fatigue never improves.
If you jump into the Paleo (or any low-carb) program and hit a brick wall because of side effects, add back your carbs until you feel better again and then try cutting down again, but go slow to give your body the time to adapt to the idea. This way, your low metabolism can gear up to give you the fat burning benefits of hibernation without having to take the four month winter snooze.
Have you experienced something similar when cutting back on carbs? Tell me in the comments below. I should highlight, I personally eat low-ish carbs, mostly because I veer toward more nutritious options when designing meals. And avoid cheap, packaged foods…which are mostly carby. But I ensure I get a good dose daily via grains and root veggies and good quality bread (not every day). I’ve worked out this is what works best for me.