Quick Summary tl;dr
Overall, it appears that although low-carb and keto diets reduce levels of thyroid hormones in the blood, this doesn't seem to impact health, ability to lose weight, or energy levels. On the contrary, many people respond to carb restriction with improvements in body composition, vigor, and health markers.
Additionally, a low-carb or ketogenic diet limited in inflammatory foods may be beneficial for those with Hashimoto's disease.
However, extreme carb restriction (ie, less than 20 grams of total carbs daily) on a long-term basis isn't advised for those with autoimmune thyroid disease. It is advisable that individuals with hypothyroidism, consume a minimum of 20 grams of net carbs (total carbs minus fiber) every day.
As with many things in nutrition, the optimal level of carb intake for thyroid health varies from person to person. Monitoring how you feel and perform, your thyroid hormone levels, and your antibody status can help you create a personalized low-carb lifestyle that is optimal for you.
Thyroid hormones affect nearly every system in the body and have a profound influence on metabolic rate and overall health. Because of this, conditions such as Hashimoto's thyroiditis can cause symptoms that negatively affect quality of life.
Is a low-carb or keto diet helpful or harmful for people with Hashimoto's disease or other hypothyroid conditions? This article will explore the impact of keto and low-carb diets on thyroid health in different populations, along with providing guidance for optimizing thyroid health.
What Are The Functions of the Thyroid Gland Hormones?
The thyroid is a small, butterfly-shaped gland situated at the front of the base of your neck. It's also been compared to a small bow tie in terms of its shape and location.
The thyroid gland's function is to take the mineral iodine and combine it with the amino acid tyrosine to form monoiodothyronine (T1), diiodothyronine (T2), and the two major hormones, triiodothyronine (T3) and thyroxine (T4). Although the thyroid gland produces more than four times as much T4 as T3, only T3 is considered the "active" form of thyroid hormone responsible for its many effects. Moreover, T4 can be converted to T3.
When needed, T3 and T4 are bound to a protein called thyroid-binding globulin (TBG) and released into the bloodstream to be transported to tissues and organs throughout the body. In the liver and other organs, most of the T4 is converted to T3, which binds to specific receptors in your cells and produces a number of metabolic effects.
However, some of the T4 is converted to reverse triiodothyronine (RT3). RT3 is essentially an inactive "mirror image" of T3 that can bind to the T3 receptor and block its effects. Although the conversion of RT3 is normal, elevated RT3 levels are often seen in times of stress or illness.
In your body's cells, T3:
- Regulates metabolic rate and calorie burning
- Controls body temperature
- Influences heart rate
- Supports brain function
- Influences muscle contraction and retention of muscle mass
- Helps maintain bone health
A number of glands work together to make sure that your body has the right amount of thyroid hormones circulating in its system.
When thyroid hormone levels are too low, your brain's hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the adjacent pituitary gland to produce thyroid-stimulating hormone (TSH). TSH then triggers the thyroid gland to increase its production of thyroid hormones and release them into the bloodstream.
By contrast, when circulating thyroid levels are higher than needed, the hypothalamus and pituitary gland produce and release less of these hormones, thereby decreasing the amount of thyroid hormone in the bloodstream.
However, in the case of thyroid disease, this system doesn't function the way it's designed to.
There are several types of thyroid disorders, but the two most common are Graves' disease and Hashimoto's thyroiditis.
Graves' disease is an autoimmune condition in which thyroid-stimulating immunoglobulin (TSI) antibodies cause the thyroid gland to produce more thyroid hormone than needed. Graves' disease is by far the most common underlying cause of hyperthyroidism, or elevated levels of thyroid hormone.
Symptoms of hyperthyroidism are typically moderate to severe and include:
- weight loss, despite increased appetite
- difficulty sleeping/insomnia
- hand tremors
- sweating and heat intolerance
- rapid heartbeat
- increased stool frequency
- bulging eyes
- goiter (enlarged thyroid gland)
- decreased menstrual flow or skipped periods
Untreated hyperthyroidism can cause changes in heart rate and rhythm that can potentially be fatal. Graves' disease is treated with radioactive iodine, surgery, and/or antithyroid medication.
Like Graves' disease, Hashimoto's thyroiditis (also known as Hashimoto's disease) is an autoimmune condition. However, instead of making antibodies that trigger the thyroid gland to produce more thyroid hormones, your body makes antibodies that gradually destroy the thyroid gland and impair its ability to make hormones, leading to hypothyroidism. The main antibodies responsible for Hashimoto's are TPO (thyroid peroxidase) antibodies and antithyroglobulin antibodies.
Hashimoto's thyroiditis is the most common cause of primary hypothyroidism, a condition in which the pituitary gland is making adequate TSH but the thyroid gland can't produce enough thyroid hormone in response. It is up to 10 times more common in women than in men, affecting an estimated 1-2% of all women ( 1). The development of Hashimoto's disease is strongly influenced by genes and environmental factors, such as infections, exposure to certain chemicals and drugs, and nutrient deficiencies.
Although a minority of people with Hashimoto's don't have any noticeable symptoms, most have one or more of the following, which can range from mild to severe:
- sluggishness and fatigue
- weight gain, despite normal or decreased appetite
- increased sensitivity to cold
- difficulty concentrating
- dry skin and hair
- hair loss
- increased menstrual flow
- goiter (enlarged thyroid gland)
During the period of time that the thyroid is being destroyed, people with Hashimoto's may occasionally switch back and forth between symptoms of hypothyroidism and hyperthyroidism. For instance, they may go from being sluggish and gaining weight easily to briefly losing weight despite eating more. Over time, however, the entire system slows down as the thyroid becomes underactive and unable to produce thyroid hormones.
Hashimoto's thyroiditis is typically diagnosed by checking for elevated levels of TPO or antithyroglobulin antibodies in the blood. However, research suggests that although about 5% of people with Hashimoto's don't have thyroid antibodies in the blood, a thyroid ultrasound or biopsy will reflect changes indicative of the disease. These people tend to have milder hypothyroid symptoms than those with elevated TPO or antithyroglobulin antibodies (2).
It's important to have a thorough lab workup done if you suspect you may have thyroid disease. Here is a list of labs that can help identify thyroid issues.
Some people have hypothyroidism that isn't due to Hashimoto's disease. Although these individuals typically have similar symptoms as those with Hashimoto's, their disease isn't autoimmune in nature.
Causes of non-autoimmune hypothyroidism include:
- abnormal growths of the thyroid gland
- certain medications, including some used to treat cancer, heart disease or depression
- defects in the pituitary or hypothalamus
- genetic defects in thyroid production (rare - usually present at birth or shortly after)
Treatment for Hashimoto's thyroiditis and other types of hypothyroidism include taking thyroid hormone replacement in the form of synthetic T4 (levothyroxine), synthetic T3 (liothyronine sodium), and/or natural porcine (pig) thyroid (Armour, Nature-Throid, or WP Thyroid).
How Do Keto and Low-Carb Diets Affect People With Normal Thyroid Function?
For decades, it's been known that starvation and very-low-calorie diets decrease the level of circulating thyroid hormones in the bloodstream ( 3, 4).
Low-carb and ketogenic diets have also been found to reduce levels of T3 in the bloodstream. This makes sense, as these diets have often been shown to induce physiological changes similar to fasting ( 5, 6).
And although a low T3 level alone doesn't indicate hypothyroidism, a recent study suggests that reduced thyroid activity may occur in some susceptible individuals who adopt a very strict keto diet.
In this 2017 study of epileptic children, 20 out of 120 subjects (over 16%) developed hypothyroidism within 6 months of starting a ketogenic diet therapy and were treated with synthetic T4 thyroid hormone ( 7).
Importantly, the classical ketogenic diet for epilepsy is severely restricted in carbs (typically less than 15 grams per day) and also low in protein. It's unknown whether adding in 10-15 grams of carb and increasing protein intake would have changed the results.
Indeed, decades-old research in healthy people suggests that the magnitude of carb restriction coupled with calorie restriction influences how much T3 levels decline.
For instance, a 1976 study of obese people showed that T3 levels dropped significantly during a carb-free 800-calorie diet but didn't change much on an 800-calorie diet providing at least 50 grams of carbs per day ( 8).
Yet even when calories aren't restricted, very-low-carb diets often lead to lower T3 levels in the blood. However, studies suggest that physical performance and metabolic rate don't appear to be affected by this reduction in T3 ( 9, 10, 11).
In one study of overweight type 2 diabetic adults who consumed a diet restricted to less than 20 grams of carbs daily, TSH levels decreased from 1.6 to 1.4 mIU/L, on average. This suggests that the study participants required less thyroid hormone, although T3 wasn't measured. In addition, they experienced several of the beneficial effects typically seen on keto diets, including weight loss and significant improvements in blood glucose control and insulin sensitivity ( 12).
It's important to note that the studies that have been done have been small and of short duration. It's likely that some people experience considerably greater changes in thyroid hormone levels - and their effects - than others do.
At this time, the impact of ketogenic and very-low-carb diets on long-term thyroid health remains controversial. Dr. Steve Phinney has suggested that being in nutritional ketosis improves thyroid hormone sensitivity, thus allowing the body to function at lower T3 levels. On the other hand, Dr. Atkins often prescribed thyroid hormone replacement for his patients whose thyroid levels dropped during the very-low-carb stages of his diet. And Dr. Cate Shanahan recommends that carb intake be reduced gradually in order to reduce potentially negative effects on thyroid health.
How Do Keto and Low-Carb Diets Affect People With Hashimoto's Disease?
A carb-restricted diet based on whole foods may be beneficial for several autoimmune conditions, including Hashimoto's thyroiditis. In fact, many people with Hashimoto's have reported improvement in symptoms after switching to this way of eating. Unfortunately, there is little formal research on keto and low-carb diets for Hashimoto's at this time. However, what exists is encouraging.
In a 2016 controlled study of 180 people with Hashimoto's disease, one group followed a high-protein, low-carb (12-15% of calories) diet. In addition, this group avoided goitrogens (compounds that interfere with thyroid function), legumes, eggs, dairy products, and gluten. The control group followed a standard low-calorie diet that didn't exclude any specific foods during the same 3-week time period ( 13).
At the end of the study, the low-carb group showed the following improvements:
- a 44% decrease in TPO antibodies
- a 40% decrease in antithyroglobulin antibodies
- a 5% reduction in body weight
By contrast, the low-calorie group experienced a 9% increase in antithyroglobulin antibodies and a 16% increase in TPO antibodies. Additionally, although both groups lost weight, the low-calorie group lost more lean mass and less fat mass compared to the low-carb group.
Case studies also support the use of low-carb diets in diabetic and obese people with Hashimoto's, when used in combination with thyroid hormone replacement ( 14, 15).
Additionally, avoiding food high in carbs and sugar may be beneficial for digestive issues. One case-control study in 45 people found that 73% of those with Hashimoto's disease displayed evidence of fructose and/or lactose malabsorption that led to symptoms like bloating, cramping, gas, and loose stools ( 16).
How Low-Carb Should You Go If You Have Hashimoto's Disease?
The low-carb diets consumed by hypothyroid individuals in the studies previously discussed contained between 60-130 grams of total carb per day, which is outside the level of ketosis for most people.
Many clinicians who work with ketogenic diets for weight loss, diabetes, or other conditions recommend that their patients with Hashimoto's avoid a drastically carb-restricted diet of less than 20 grams of total carb per day.
Endocrinologist Dr. Broda Barnes, who spend decades researching thyroid function and worked with hundreds of thyroid patients, recommended a minimum of 30 grams of net carbohydrate (total carbs minus fiber) for individuals with hypothyroidism, in conjunction with thyroid replacement.
If you have Hashimoto's and want to follow a keto diet, it seems wise to avoid extremely severe carb restriction for extended periods of time.
Similarly, although mild intermittent fasting (such as eating all meals within an 8-hour window) is fine, prolonged fasting of 24 hours or more isn't recommended for people with Hashimoto's because it places undue stress on the thyroid.
Foods To Avoid or Limit With Hashimoto's Thyroiditis
Avoiding or limiting certain foods if you have Hashimoto's may help reduce symptoms or potentially even slow down disease progression.
Since certain foods are known to exacerbate autoimmune disease, removing them from your diet or sharply cutting back may potentially lead to improvement in symptoms and/or disease progression.
Here is a list of the most common offenders:
- gluten, in part due to the connection between autoimmune thyroid disease and celiac disease, which is characterized by an inability to absorb gluten
- other grains, especially those that contain gluten, such as wheat, barley, and rye
- legumes, including beans, lentils, and peanuts
Dr. Izabella Wentz, a pharmacist with Hashimoto's, reports that following the Autoimmune Paleo Diet (AIP) has been successful in helping many of her readers and patients reduce symptoms and thyroid antibodies. However, this approach is quite strict because in addition to the foods above, it excludes eggs, dairy, nuts and seeds, caffeine, and alcohol.
We are all different and what works for one person may not work for another. Start with the basic recommendations to follow a carb-restricted approach and avoid gluten, grains, legumes and soy. If the symptoms persist more than two months after making these changes, consider excluding some or all of the foods listed in the AIP protocol.
Many plants contain goitrogens, compounds that can interfere with the thyroid's ability to take in iodine and inhibit the action of TPO.
Goitrogens are found in several healthy low-carb vegetables, including:
- bok choy
- Brussels sprouts
- collard greens
Because they provide antioxidants, micronutrients, and fiber, giving up these vegetables altogether isn't recommended. Fortunately, sufficient iodine intake can counteract the potentially negative effects of goitrogens.
In addition, fermenting, microwaving, steaming, or boiling these vegetables can reduce their goitrogen content by 33-50% or more, depending on the length of cooking time ( 17).
Nutrients To Focus On With Thyroid Disease
Because iodine is needed for thyroid hormone creation, getting enough in your diet is crucial. However, extremely high doses of iodine can be problematic as well. In one study, a portion of Danish children and adults who took part in a conservative iodized salt supplementation program were found to be at increased risk of developing autoimmune thyroid disease ( 18).
The Recommended Dietary Allowance (RDA) for iodine is 150 mcg for most people and 220 mcg for pregnant women.
Supplementing with iodine is a controversial area. While iodine deficiency is more prevalent in developing countries, anyone may become iodine deficient. On the other hand, too much iodine may have negative effects on your thyroid, such as increasing risk of autoimmune thyroiditis or goiter. Some experts recommend that people supplement with iodine because it counteracts the halogens (fluoride, chloride, bromide) that we're exposed to every day. However, others take a more conservative stance and argue that a balanced diet can provide all the iodine the body needs.
The best sources of iodine include seafood and iodized salt, which provides 100 mcg per 1/4 teaspoon.
Selenium aids in converting T4 into the active thyroid hormone T3. A recent 2017 review concluded that selenium supplementation may be beneficial in those with Hashimoto's thyroiditis who have low selenium blood levels ( 19). However, this must be coupled with adequate iodine intake.
The recommended daily intake for selenium is 100-400 mcg per day.
The best food source of selenium is Brazil nuts, which provide about 50 mcg apiece, on average. However, Brazil nuts vary in size and selenium content. Additional sources include other nuts, seafood, poultry, and meat, including organs.
Researchers have shown a link between low vitamin D status and Hashimoto's thyroiditis ( 19, 20).
In one study, providing high-dose vitamin D therapy to deficient adults with Hashimoto's resulted in normalization of their serum vitamin D levels and a 20% reduction in TPO antibodies ( 20).
Sun exposure is the best way to increase vitamin D levels naturally. Vitamin D can also be obtained from regular consumption of fatty fish such as mackerel, salmon, and sardines. However, for some people, supplementation may be required in order to maintain serum levels within the optimal range of 30-60 ng/mL.
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