One of the recurring arguments against long-term carbohydrate restriction is that it may lower thyroid function, making this lifestyle unsustainable and potentially harmful.<\/p>\n
At the same time, some experts and low-carb advocates have come out and say that, in most cases, this decrease in thyroid output is normal and perhaps even preferable\u00a0to an hyperactive thyroid.<\/p>\n
In the sea of conflicting opinions and advice, how do we determine if low-carb diets really are dangerous for thyroid health? This is an intriguing and multifaceted conversation, which harbors many questions:<\/p>\n
Is there a threshold of carbs under which issues with the thyroid start to appear?<\/p>\n
Can following a cyclical low-carb diet help circumvent them?<\/p>\n
Should people with pre-existing thyroid disorders avoid low-carb dieting?<\/p>\n
Hold on as we discuss in this article the various perspectives on this often controversial topic.<\/p>\n
Low-carb(ing) and thyroid drama<\/strong><\/p>\n This hotly contested nutritional debate started with the observation that some people do incredibly well following a low carb diet long term, while others\u00a0crash and burn on this type of dietary plan.<\/p>\n The concept that low-carb diets lead to lower thyroid function has been heavily promoted in the low-carb\/paleo circles by highly-respected practitioners, like Paul Jaminet or Chris Kresser, who see patients who\u00a0present with symptoms such as:<\/p>\n For many doctors, these can be considered to be evocative of problems with the thyroid, especially low thyroid function (hypothyroidism).<\/p>\n The main reason why carbs affect thyroid function so directly is because insulin activates the enzymes that are needed for the conversion of the inactive T4 thyroid hormone into its active T3 form, and insulin is generally quite low on very low-carb diets. Hence why carb restriction\u00a0is thought to be limiting this conversion.<\/p>\n But, some have argued, that unless the thyroid-stimulating hormone (TSH) – the hormone that stimulates the production of T4 and then T3 – rises to very high values, which would indicate that the conversion described earlier is inadequate, there is no need to worry about thyroid issues on low carb diets.<\/p>\n This is because in the case of hypothyroidism, TSH is high but the thyroid hormones, specifically, free T3 and free T4, can still be in the normal range. TSH has an inverse relationship with thyroid hormones: when it\u2019s high, it suggests that the thyroid is under-functioning, and when it\u2019s low, it suggests that the thyroid gland is over-functioning.<\/p>\n Low thyroid on low-carb: Myth or fact?<\/b><\/p>\n Two of the top low-carb nutritional health researchers in the world – Dr. Stephen Phinney and Dr. Jeff Volek – say this phenomenon with low thyroid while on a low-carb diet is a “myth” and has not manifested itself\u00a0in any of the research subjects in their numerous studies conducted over the past three decades of people properly following a low-carb diet with adequate calories.<\/p>\n However, it is important to note that because of the expensive nature of nutrition research, there is a lack of extended observational studies and, in particular, there is a dearth of studies looking at the effects of low-carb diets long term.<\/p>\n The studies that have been done by Phinney and the like also didn’t include full thyroid panels so the fact that thyroid problems\u00a0haven’t come up in those studies, especially in ones with very short follow-up periods measured\u00a0in weeks does not mean that it is a non-issue.<\/p>\n In terms of the effects of\u00a0diet on thyroid physiology, it is very well documented in the scientific literature that calorie restriction and fasting also decrease the conversion of T4 into T3 while increasing the conversion of T4 into reverse T3, which is an inactive form of thyroid hormone considered a metabolic dead end – once it’s converted into reverse T3, it can’t be re-converted back into active T3.<\/p>\n One landmark study, known as The Vermont Study, confirmed that T3 is very sensitive to both calorie and carb intake and showed that when calories AND carbs are too low, T3 levels drop.<\/p>\n For that reason, Dr. Phinney and others believe that the primary point of contention revolves around consuming an adequate amount of calories with a low-carb diet\u00a0in order to normalise thyroid function without the necessity for consuming added carbs.<\/p>\n The ‘slowing-down-of-the-engine’ interpretation\u00a0<\/strong><\/p>\n Dr. Ron Rosedale, who is one of the originators of a very high-fat, moderate protein, low-carb diet and is well-read\u00a0on the effects of extended periods of low-carb dieting, has argued that what’s perceived as hypothyroidism symptoms on low-carb diets is actually a sign of a natural slowing down of the thyroid.<\/p>\n What he has observed in his patients is that TSH and T3 levels went down on a low-carb diet in what he calls a “purposeful reduction in thyroid function”, not hypothyroidism (which would be signaled by a high TSH).<\/p>\n According to Rosedale, thyroid function is not going down because it has to\u00a0<\/em>but rather because it\u00a0wants to,\u00a0<\/em>which is part and parcel of a genetic phenotype of maintenance and repair that has been previously observed in calorie-restricted animals as a mean to temper the thyroid.<\/p>\n The analogy he often uses to describe this is one of a car that works really well and is tuned properly and therefore doesn’t have to rev as high. It will still have greater acceleration and better mileage, which in this case would translate into longevity.<\/p>\n The thyroid and adrenals\u00a0connection<\/strong><\/p>\n The pituitary gland (for thyroid hormone) and adrenal glands work together (= the hypothalamic-pituitary axis or HPA axis) to supply essential hormones and deliver them where they need to be throughout the body. When the adrenal glands aren’t producing the right amount of the stress hormone cortisol and this accompanied by a thyroid problem, it can make the situation much worse.<\/p>\n\n