Is Low-Carb Wrecking Your Thyroid? Maybe not..

Written By emma davies

In the world of nutrition and Functional Medicine, few topics spark as much confusion and controversy as the relationship between low-carb diets and thyroid health. For many, the thyroid is a mysterious gland blamed for everything from weight gain to fatigue. Add in the rising popularity of ketogenic and low-carb lifestyles, and you get a sea of misinformation and confusion. One voice helping to clear the waters is Dr. Ben Bikman, a leading metabolic scientist and advocate for low-carb nutrition.

In this  blog, I’ll explore how low-carb diets affect thyroid hormones, explain the science behind the perceived drop in T3, and show why that might not be a bad thing . This blog was inspired and, is mostly grounded in, the work and research of Dr. Ben Bikman. Dr Bikman is a hugely respected academic who specialises in metabolic disorders. I really respect his work and his dedicated research into all matters around insulin, metabolism and endocrine health.

 Understanding the Thyroid: What It Does and Why It Matters

The thyroid is a small gland in your neck that plays a big role in metabolism. It produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T3 is the active form and responsible for regulating energy use, body temperature, and more.

These hormones are regulated by the hypothalamic-pituitary-thyroid (HPT) axis. When T3 and T4 levels drop, the brain signals the pituitary gland to release thyroid-stimulating hormone (TSH), which prompts the thyroid to produce more hormones. This feedback loop ensures hormonal balance.

Low-Carb Diets: What Changes in Thyroid Hormones?

Research shows that people following low-carb or ketogenic diets often see a drop in circulating T3 levels. This discovery has caused concern, with many assuming it signals thyroid dysfunction. However, as Dr. Bikman points out, context matters.

Dr. Bikman explains that while T3 levels may drop on a low-carb diet, TSH levels usually remain stable. This is critical: if the body truly lacked thyroid hormone, the brain would respond by increasing TSH to demand more. If TSH doesn’t rise, the body isn’t interpreting the lower T3 as a problem.

Why Does T3 Decrease on a Low-Carb Diet?

According to Dr. Bikman, the decrease in T3 isn’t necessarily a sign of malfunction (and in fact he believes it probably isn’t) – but instead a sign of increased efficiency.  This makes sense and here's why:

  1. Lower Insulin, Lower Demand: On a low-carb diet, insulin levels drop. Since insulin resistance often coexists with thyroid resistance, lowering insulin improves the body’s response to thyroid hormones. In this scenario, the body may need less T3 to get the same job done.

  2. Glucose Requirements Decline: T3 plays a role in stimulating glucose uptake and metabolism. On a low-carb diet, your body shifts toward using fat and ketones for fuel instead of glucose. The reduced need for glucose lowers the demand for T3.

  3. Improved Sensitivity: Think of T3 like a key and your cells like locks. If your locks become more sensitive, you need fewer keys. Dr. Bikman emphasizes that the drop in T3 is a sign that the "locks" are working better.  I believe this is a clever supposition.

Thyroid Resistance and Metabolic Dysfunction

Many individuals with obesity or insulin resistance also have an elevated TSH but also an elevated T4, which suggests thyroid resistance. Nomally an elevated TSH accompanies a LOW T4 level. This means their bodies are producing hormones, but the cells aren’t responding properly. A low-carb diet can reduce this resistance, potentially normalizing thyroid hormone use and reducing the need for excess T3.

This improvement isn’t always reflected in traditional lab markers. A drop in T3 might look alarming on paper, but if TSH is normal and symptoms improve, it’s a sign the body is adapting efficiently and the low T3 is therefor NOT of concern.

What Does the Research Say?

Numerous studies support this position. A review of clinical data shows that while T3 often decreases with carbohydrate restriction, this is not accompanied by a rise in TSH or hypothyroid symptoms. In fact, many people report better energy, weight loss, and improved mental clarity.

Dr. Bikman writes in his blog: “There is no evidence that a ketogenic or low-carbohydrate diet harms the thyroid. Lower T3 is not a sign of disease but of metabolic efficiency.”

How to Know If Your Thyroid is Healthy on a Low-Carb Diet

Here are a few guidelines to assess your thyroid health if following a lower carb diet:

  • Check TSH: This is the most sensitive marker. If it's within normal range, your thyroid is likely functioning well.

  • Monitor Symptoms: Are you experiencing fatigue, hair loss, weight gain, cold intolerance, or depression? If not, a lower T3 may not be concerning.

  • Compare Labs Over Time: Look at trends rather than one-off numbers. If you feel well and TSH remains stable, you likely have nothing to worry about.

When to Seek Help

If you start experiencing classic hypothyroid symptoms or see a rising TSH alongside a falling T3, it’s worth consulting a practitioner well versed in endocrinology.  Some individuals may have pre-existing thyroid conditions that require support regardless of diet.

To summarise:

Redefining Thyroid Health in a Low-Carb Context

Low-carb diets may lead to lower T3 levels, but this doesn’t mean the thyroid is underperforming. Instead, as Dr. Ben Bikman argues, it could indicate that your body has become more metabolically efficient. If TSH remains stable and you're feeling energetic and healthy, there is likely no cause for concern.

Ultimately, thyroid health is about more than just lab values. It’s about how you feel, how your metabolism functions, and whether your body is thriving. Don’t let outdated assumptions prevent you from reaping the benefits of a low-carb lifestyle.

References

 

 
emma davies
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