The ketogenic diet, often called the keto diet, has surged in popularity as a weight-loss strategy. However, its impact on thyroid health, particularly its interaction with conditions like hyperthyroidism and hypothyroidism, warrants careful consideration. This article explores the intricate relationship between the ketogenic diet and thyroid function, examining potential benefits, risks, and necessary modifications for individuals with thyroid conditions.
Understanding the Ketogenic Diet
The ketogenic diet is a high-fat, moderate-protein, and very low-carbohydrate eating pattern. The typical macronutrient ratio is 55-60% fat, 30-35% protein, and 5-10% carbohydrate. For a standard 2000-calorie diet, this translates to no more than 50 grams of carbohydrates per day-about the amount in a single bagel.
Ketosis Explained
The keto diet mimics a fasting state, depriving the body of its preferred energy source: carbohydrates. When carb intake is restricted, the body first uses glycogen stores in the liver and muscles. Once these stores are depleted (typically within 12 hours), the body enters ketogenesis.
During ketogenesis, fat stores are broken down to create ketone bodies, which serve as an alternative fuel source. The heart, muscles, kidneys, and brain can use ketone bodies for energy, though red blood cells and the liver cannot. Ketone bodies also possess cell-protective antioxidant properties. Essentially, ketosis is a survival mechanism that allows the body to continue functioning in the absence of sufficient carbohydrates.
Recognizing Ketosis
The "keto flu" is a common set of symptoms that can indicate the body is entering ketosis. These symptoms may include:
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- Brain fog
- Sore muscles/cramps
- Dizziness
- Keto-breath
- Headache
- Fatigue
These symptoms are usually short-term and can be mitigated by staying hydrated. More accurate methods for confirming ketosis include urine ketone strips, breath tests, and blood tests.
A Brief History
Originally, the keto diet was used to treat childhood epilepsy. As anti-epileptic medications advanced, the diet's popularity waned until the 2010s, when celebrities and social media influencers began promoting its weight-loss benefits.
Potential Benefits
The keto diet has some research-backed benefits, including improved blood sugar control, better lipid panels, and weight loss. A 2021 review outlines potential health benefits of the keto diet, such as:
- Improved appetite management
- Weight loss
- Reduced visceral fat
- Increasing “good” cholesterol and lowering “bad” cholesterol
- Reducing the need for insulin in diabetes
However, further research is needed to determine if these benefits outweigh the risks for people with hypothyroidism.
Potential Risks
A 2023 paper indicates that the keto diet may cause short-term and longer-term effects. Short-term effects include "keto flu," with symptoms such as nausea, vomiting, constipation, headaches, dizziness, insomnia, fatigue, and reduced exercise tolerance.
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Longer-term effects may include:
- Nutrient deficiencies
- Digestive issues (constipation, diarrhea, bloating)
- Kidney stones
- Heart disease
- Muscle loss
- Cognitive decline
The Thyroid Gland: A Master Regulator
The thyroid, a small gland located in the front of the neck below the voice box, plays a crucial role in development and metabolism. It constantly regulates various bodily functions, including:
- Heat regulation
- Heartbeat
- Metabolism
- Speed of digestion
- Muscle contraction
The thyroid secretes two primary hormones:
- T4 (thyroxine): The inactive form of T3, converted as needed.
- T3 (triiodothyronine): The biologically active hormone that regulates metabolism in cells.
T3 essentially tells cells how quickly to work. High T3 levels can lead to hyperthyroidism (cells working too quickly), while low T3 levels can lead to hypothyroidism (cells working too slowly).
Hypothyroidism Explained
Hypothyroidism occurs when the thyroid gland doesn't produce enough thyroid hormone to support the body's functions. This slows metabolism and can cause symptoms like fatigue, weight gain, slowed heart rate, reduced tolerance to cold, joint and muscle pain, dry skin or hair, heavy or irregular menstrual periods, fertility problems, and depression.
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The Interplay Between Keto and Thyroid Function
The ketogenic diet has the potential to detrimentally alter thyroid hormone levels. Research suggests that periods of starvation (which the keto diet mimics) and weight loss from the keto diet can lower T3 levels, potentially leading to weight gain.
From a biological perspective, it makes sense for the body to lower T3 production during caloric/carbohydrate restriction, as lower T3 means less energy expenditure. When the body perceives a "famine," metabolism downregulates to conserve energy.
Research Findings
A 2022 study explored the effects of the keto diet on thyroid function and metabolism in 11 participants without thyroid disease. The participants followed a high-carbohydrate, low-fat (HCLF) diet for three weeks, followed by a one-week interval and then a keto diet for three weeks. Calorie intake was matched across diets.
The researchers found that participants lost more weight on the keto diet. While T4 concentrations remained unchanged, T3 concentrations decreased more on the keto diet than on the HCLF diet. This suggests that the keto diet may promote weight loss through changes in thyroid function and metabolism in healthy individuals.
A 2020 review also outlines a similar relationship between low-glycemic diets like the keto diet and thyroid function.
However, neither study indicates whether the keto diet is safe and effective for individuals living with hypothyroidism or other forms of thyroid disease.
A study published in the Journal of Pediatric Endocrinology and Metabolism evaluated thyroid function in children following the ketogenic diet for at least 1 year due to pharmacoresistant epilepsy. The study included 120 patients, roughly half of whom were male (n = 63), with a mean age of 7.3 ± 4.3 years. Patients were stratified according to their baseline TSH levels: those with elevated TSH levels (TSH >5 mIU/L; 14 patients) and patients with normal TSH levels (TSH <5 mIU/L; 106 patients). Hypothyroidism was diagnosed more commonly in those with an elevated baseline TSH level compared with those with a normal TSH at baseline (71.4% vs. 9.4%; P <.001). A total of 20 patients were diagnosed with subclinical hypothyroidism and started on L-thyroxin in the first 6 months of ketogenic diet therapy. More females were noted to have hypothyroidism than to not have thyroid dysfunction. No patients were diagnosed with hyperthyroidism. Several antiepileptics affect thyroid function, so results were stratified based on drug therapy, and no difference was found in thyroid levels. Although there are several limitations to this single-center study, the authors concluded that the ketogenic diet might cause hypothyroidism in children with refractory epilepsy. Female gender and higher TSH levels at baseline were found to be independent risk factors for hypothyroidism in patients following the ketogenic diet. Additionally, there is controversy in the literature about treating subclinical hypothyroidism in children. At a minimum, thyroid function should be monitored in children being treated with the ketogenic diet.
How the Ketogenic Diet Affects Thyroid Function
The ketogenic diet (KD), a high-fat, low-carbohydrate diet, causes profound metabolic adaptations that go beyond energy production and affect endocrine function and thyroid hormone regulation. By shifting the body’s primary fuel source from glucose to fatty acids and ketones, the KD alters insulin signaling, inflammation levels and deiodinase activity, which together affect thyroid hormone metabolism.
The HPT axis governs the regulation of thyroid hormone production through a tightly coordinated negative feedback loop. In this axis, the hypothalamus secretes TRH, which stimulates the anterior pituitary to release TSH.
Under ketogenic dietary conditions, the HPT axis undergoes characteristic adaptations in response to sustained carbohydrate restriction and altered metabolic signaling. One of the most consistent findings is a reduction in circulating free T3 (fT3) levels, often without a corresponding rise in TSH, suggesting a non-pathological downregulation of thyroid activity. This T3 reduction is hypothesized to mimic the physiological response seen during fasting or marked caloric restriction, while TSH remains stable because central feedback perceives the lower T3 as an adaptive, not a pathological, state.
Low carbohydrate availability decreases insulin secretion, which in turn suppresses deiodinase activity and impairs T3 production. Simultaneously, levels of reverse T3 (rT3)-an inactive isomer of T3-may rise, by activation of DIO3, further reducing the pool of biologically active thyroid hormone. This shift in DIO activity appears to be a deliberate physiological response to lower energy availability, aimed at reducing basal metabolic rate and preserving energy stores.
Studies consistently report that TSH remains within the normal range during KD adherence, even as T3 declines. This dissociation suggests that lower T3 on KD should not be automatically interpreted as hypothyroidism, especially in the absence of clinical symptoms. Rather, it reflects a homeostatic recalibration in which the hypothalamus and pituitary do not perceive the lower T3 as a pathological deficit, likely due to compensatory changes in cellular energy signaling and mitochondrial function. Additionally, ketone bodies themselves, particularly BHB, may influence HPT axis signaling. Experimental findings suggests that BHB can modulate TRH and TSH secretion at the hypothalamic and pituitary levels, possibly dampening the drive for increased thyroid hormone production under low-glucose conditions.
Hormonal Influences
Beyond direct nutrient effects, the KD induces substantial shifts in hormonal signaling that indirectly affect thyroid hormone metabolism and HPT axis regulation. Four hormones-leptin, insulin, cortisol, and ghrelin-are particularly important in this context due to their regulatory influence on TRH and TSH secretion, deiodinase activity, and energy balance.
- Leptin: Leptin, a hormone produced by fat cells, is a key regulator of energy balance and directly influences the TRH expression in the hypothalamus. Under KD, weight loss and reduced adiposity lead to significant decreases in leptin levels, which decrease TRH output and downregulate TSH secretion.
- Insulin: Insulin is a key metabolic hormone that can regulate DIO2 activity, particularly in brown adipose tissue, skeletal muscle and glial cells thereby facilitating the local conversion of T4 to active T3. In the context of KD, insulin levels fall sharply due to low carbohydrate intake, thereby reducing deiodinase stimulation and contributing to lower circulating T3 concentrations.
- Cortisol: Cortisol, a glucocorticoid released in response to stress, typically rises during the early phase of ketogenic diet adaptation, reflecting a heightened stress response that mobilizes gluconeogenic substrates and helps maintain blood glucose. Sustained cortisol elevation can suppress the HPT axis by inhibiting TRH expression, reducing TSH secretion, and impairing deiodinase activity.
- Ghrelin: Ghrelin, primarily known as an orexigenic hormone that increases appetite, also interacts with the HPT axis, generally suppressing TSH and influencing thyroid hormone levels, but the direction and magnitude of these effects depend on physiological context and species.
Is Keto Safe for Someone with a Thyroid Condition?
The keto diet is not the best hormone-balancing diet and has the potential to detrimentally alter thyroid hormone levels. If you have a thyroid condition, you may see initial positive results on the keto diet, but over time, you may develop symptoms such as increased tiredness and weight gain as a result of your body's response to the low-carb diet, which is to lower T3 production.
There is no "one-size-fits-all" rule when it comes to determining the safety of the keto diet if you have a thyroid condition, as each body responds uniquely. It is essential to be in tune with how you are feeling when making any lifestyle change like starting a keto diet.
If your energy levels are normal, you’re able to think clearly, and you’re making progress with your weight goals, you likely don’t have much to worry about with the keto diet. However, if you are experiencing adverse symptoms that last a long time, such as fatigue or an inability to lose weight, that is an indication your thyroid hormones might be unbalanced. If this happens to you, the best way to see if your hormone levels are off is to get a blood test.
Contraindications
The keto diet may not suit everyone, particularly individuals with:
- Pancreatitis
- Liver failure
- Disorders of fat metabolism
- Certain deficiencies (primary carnitine deficiency, carnitine palmitoyltransferase deficiency, carnitine translocase deficiency, pyruvate kinase deficiency, porphyria)
Individuals with diabetes who are taking insulin or other medications should consult a doctor before starting the keto diet, as medication dosages may need adjustment to prevent severe hypoglycemia.
How to Modify the Keto Diet for Thyroid Health
At-home lab testing can give you direct insight into the impact the keto diet has on your thyroid hormone levels. By tracking the impact different adjustments have on your bloodwork, you can find your optimized ketogenic diet. Some adjustments you can make include:
- Intermittent fasting
- Adjusting carb, protein, and fat ratios
- Reducing consumption of foods you may be sensitive to, such as gluten, dairy, or soy
- Balancing lifestyle factors like sleep, exercise, and stress management
In as little as one month, you can see the impact a lifestyle change has on your thyroid hormone levels.
Staying on Top of Your Thyroid While on Keto
If you have a thyroid condition, you may see initial positive results on the keto diet. But over time, you may develop symptoms such as increased tiredness and weight gain. These symptoms may be a result of your body’s response to the low carb diet, which is to lower T3 production.
While there are potential risks for going keto with a thyroid condition, there are steps you can take to increase your chances of success on the diet.
If your energy levels are normal, you’re able to think clearly, and you’re making progress with your weight goals, you likely don’t have much to worry about with the keto diet. However, if you are experiencing adverse symptoms that last a long time, such as fatigue or an inability to lose weight, that is an indication your thyroid hormones might be unbalanced. If this happens to you, the best way to see if your hormone levels are off is to get a blood test.
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