Low-Carb Diets & Thyroid Health - 3 Things You Need To Know
A low-carb diet has gained traction (especially on social media) for its benefits in weight loss, blood sugar regulation, and metabolic health. However, its impact on thyroid function is often overlooked. The thyroid plays a crucial role in energy metabolism, hormone regulation, and overall well-being, and drastic carb restriction can sometimes disrupt its function.
If you’re considering a low-carb diet, here are three key things to know about how it may affect your thyroid health—and what you can do to optimise your approach.
1. Carbohydrate Restriction Can Lower Thyroid Hormone Levels
Your thyroid relies on carbohydrates to maintain optimal function. When carb intake drops too low for extended periods, it can lead to reduced levels of T3, the active thyroid hormone.
How Does This Happen?
- Carbs influence thyroid hormone conversion: T3 (triiodothyronine) is the active thyroid hormone, and its production requires glucose availability. If carbs are too low, T4 (thyroxine) conversion to T3 slows down, leading to lower energy levels and metabolic slowdown.
- Caloric restriction & stress response: A very low-carb diet can mimic starvation, triggering the body to conserve energy by reducing thyroid output.
- Cortisol imbalance: Low-carb diets can sometimes increase cortisol levels, which can suppress thyroid function over time.
Who Might Be Affected?
- Women are more sensitive to thyroid changes, especially those with hypothyroidism or Hashimoto’s.
- Individuals with high stress levels (stress already impacts thyroid function, and extreme carb restriction can worsen it).
- Athletes & active individuals as intense training increases carb demands, and going too low-carb may impair performance & recovery.
Note: While reducing processed carbs is beneficial, going too low-carb (e.g., under 50g/day) for extended periods may negatively impact thyroid function.
2. Carbs from Whole Foods vs. Processed Foods: Not All Are Equal
One of the biggest misconceptions about low-carb diets is that all carbs are bad. The truth is, carb quality matters just as much as carb quantity—especially when it comes to thyroid health.
Whole-Food Carbs vs. Processed Carbs
- Whole-Food Carbs: Found in fruits, root vegetables (sweet potatoes, beets), and legumes, these carbs contain fibre, vitamins, and minerals that support thyroid function and metabolism.
- Processed & Refined Carbs: White bread, pastries, and sugary cereals are stripped of nutrients and cause blood sugar spikes, which can contribute to insulin resistance and metabolic dysfunction over time.
Why Whole-Food Carbs Matter for the Thyroid
- Provide fibre & micronutrients: Essential minerals like selenium, zinc, and iodine (found in whole foods) support thyroid function.
- Stabilise blood sugar: Extreme blood sugar fluctuations can increase stress hormones, impacting thyroid regulation.
- Help maintain gut health: A healthy gut microbiome is crucial for thyroid hormone conversion—and whole-food carbs support gut bacteria.
Note: Instead of eliminating all carbs, first try to focus on whole-food sources that support thyroid function, rather than relying on refined carbs.
3. A Low-Carb Diet Isn’t One-Size-Fits-All for Thyroid Health
Not everyone benefits from the same level of carbohydrate intake—especially those with thyroid imbalances. Factors like age, activity level, stress levels, and metabolic health all influence how your thyroid responds to carb restriction.
Who May Benefit from a Low-Carb Diet?
- People with insulin resistance or type 2 diabetes: Lowering carb intake can improve blood sugar control and insulin sensitivity, indirectly supporting thyroid health.
- Those who feel energised on a low-carb diet: If you experience steady energy, good digestion, and balanced hormones, your body may tolerate lower-carb intake well.
- Individuals who eat nutrient-dense whole foods: If you focus on iodine, selenium, and zinc-rich foods, your thyroid may function optimally even on lower-carb intake.
Who Should Be Cautious with a Low-Carb Diet?
- People with hypothyroidism or Hashimoto’s: Some may experience lower T3 levels, increased fatigue, and metabolic slowdown if carbs drop too low.
- Highly active individuals or athletes: A low-carb diet may impair muscle recovery, endurance, and thyroid hormone production.
- Women, especially those with hormonal imbalances: A very low-carb diet may disrupt estrogen, progesterone, and thyroid hormone balance, affecting menstrual cycles and metabolism.
How to Personalise Your Approach for Thyroid Health
- Try a Moderate Low-Carb Diet Instead of Keto – Instead of extreme keto (20-50g carbs/day), aim for 75-150g of whole-food carbs daily.
- Prioritise Nutrient-Dense Foods – Include iodine (seafood, eggs), selenium (Brazil nuts, beef kidney), and zinc (beef, pumpkin seeds) for thyroid support.
- Listen to Your Body – If you feel chronically fatigued, moody, or experience hormonal imbalances, you may need to adjust your carb intake.
Note: A low-carb diet isn’t for everyone, and thyroid health should be a top consideration before making drastic dietary changes.
Final Thoughts: Should You Try a Low-Carb Diet for Thyroid Health?
A low-carb diet can offer metabolic benefits for some, but its impact on thyroid health is highly individual.
- If you have thyroid issues, be cautious with drastic carb restriction, and focus on whole-food sources instead of eliminating carbs completely.
- If you experience low energy, cold intolerance, or hormonal disruptions, your carb intake may be too low for your thyroid needs.
- If you’re unsure, start with a moderate approach—not too high, not too low—and adjust based on your symptoms.
Your thyroid is the engine of your metabolism—fuel it wisely!
