Does Keto Suppress Your Thyroid Function?
Does Keto Suppress Your Thyroid Function?
TL;DR
Keto suppresses thyroid in most people. Low carbs reduce T4-to-T3 conversion. T3 drops. Metabolism slows. Initial weight loss from water and fat. Then plateau. Energy crashes. Sleep worsens. Women lose periods. Add back carbs (150-250g daily). Temperature rises. Metabolism recovers. Fat loss resumes eating more food.
You started keto.
First month was great. Lost ten pounds. Mental clarity. Energy high.
Month two. Three. Four. Weight loss stopped. Energy crashed. Can't sleep. Mood tanked.
Women: period disappeared. Men: libido gone.
You added more fat. Cut carbs to zero. Tried carnivore.
Still broken. Cold all the time. Hair falling out. Exhausted.
Keto worked. Then it destroyed your thyroid.
Keto is like running a car on reserve fuel. Works short-term. But engine wasn't designed for it long-term. Eventually, it breaks down.
How Keto Suppresses Thyroid
Thyroid hormone conversion requires glucose.
Conversion requires:
- Glucose
- Insulin (signals fed state)
- Selenium
- Zinc
- Adequate calories
On keto:
- Very low glucose
- Low insulin (signals starvation)
- Body perceives scarcity
Result:
- T4-to-T3 conversion decreases
- T4 converts to Reverse T3 (inactive, blocks T3)
- Free T3 drops
- Metabolism slows
This is physiological. Not pathological. But problematic long-term.
The Timeline
Week 1-4 (honeymoon phase):
- Water weight drops (5-10 lbs)
- Ketones rise (mental clarity)
- Appetite decreases
- Fat burning increases
- Energy feels good (running on stress hormones)
Week 5-12 (adaptation struggles):
- Weight loss slows or stops
- Energy becomes inconsistent
- Sleep quality declines
- Exercise performance drops
- Mood swings increase
Month 4+ (metabolic suppression):
- Temperature drops below 97.8°F
- Chronic fatigue
- Hair loss
- Women: irregular or missing periods
- Men: low testosterone symptoms
- Can't lose more weight despite extreme restriction
Some people do fine on keto. Most don't long-term.
Who Keto Helps (Short-Term)
Good candidates for 4-12 weeks:
- Severe insulin resistance (pre-diabetes, type 2 diabetes)
- Very high triglycerides
- Epilepsy (therapeutic use)
- Metabolically healthy men (tolerate better than women)
Even then: Monitor thyroid function. Track temperature. Add carbs back if symptoms develop.
Who Keto Hurts
Bad candidates:
- Women trying to conceive
- Women with PCOS or hormone issues
- Anyone with existing hypothyroid
- Athletes
- People with history of disordered eating
- Chronic stress or poor sleep
For these groups: Keto often worsens symptoms. Carbs are needed.
Keto vs. Low-Carb vs. Moderate-Carb
Keto (under 50g carbs):
- Suppresses thyroid in most people
- Not sustainable long-term for most
- May help severe insulin resistance short-term
Low-carb (50-100g):
- Still suppresses thyroid for many
- Better than keto but not optimal
- May work for metabolically healthy men
Moderate-carb (150-250g):
- Supports thyroid function
- Sustainable long-term
- Allows athletic performance
- Maintains hormones
- Works for most people
We recommend moderate-carb for metabolic optimization.
How to Transition Off Keto
If keto suppressed your thyroid:
Step 1: Add carbs gradually
- Week 1: Add 50g carbs daily (fruit, white rice)
- Week 2: Add another 50g (total 100g)
- Week 3: Add another 50g (total 150g)
- Stabilize at 150-250g daily
Step 2: Expect temporary weight gain
- Glycogen refills (1g carbs holds 3-4g water)
- Gain 3-7 lbs in week 1-2 (water, not fat)
- This is GOOD. Metabolism recovering.
Step 3: Monitor temperature
- Track waking oral temperature daily
- Should rise from <97.8°F toward 98.0-98.6°F
- Rising temperature = thyroid recovering
Step 4: Be patient
- Week 2-4: Energy stabilizes
- Week 4-8: Temperature normalizes, sleep improves
- Month 3-6: Hormones return, hair regrows, fat loss resumes
Most people feel dramatically better within 8 weeks of adding carbs back.
What About "Clean Keto"
Clean keto (whole foods, no seed oils): Better than standard keto (which often includes seed oils in dressings, fat bombs, etc.).
But still: Low carbs still suppress thyroid. Whether carbs come from whole foods or not doesn't matter. Thyroid needs glucose.
- Whole foods (yes)
- No seed oils (yes)
- Adequate carbs 150-250g (yes)
Testing Your Thyroid on Keto
If doing keto, monitor thyroid:
Labs every 3 months:
- TSH
- Free T4
- Free T3
- Reverse T3
Red flags:
- Free T3 dropping (even if still in "normal" range)
- Reverse T3 rising
- TSH rising above 2.0
If these occur: Add carbs back immediately. Don't wait for severe symptoms.
Can You Do Keto Long-Term?
Some people can. Minority.
Indicators you might tolerate keto:
- Temperature stays 98°F+
- Energy remains high
- Sleep quality stays good
- Women: periods remain regular
- Men: libido and strength normal
- Athletic performance maintained
Most people don't meet these criteria on long-term keto.
If you develop symptoms: Add carbs. Don't force a diet that's breaking your body.
FAQ
Q: I lost weight on keto. Why should I add carbs? A: If temperature is below 97.8°F, metabolism is suppressed. Weight loss will plateau. Adding carbs recovers metabolism. Long-term fat loss improves.
Q: Won't adding carbs make me gain fat? A: You'll gain 3-7 lbs of water (glycogen stores). Then weight stabilizes. As thyroid recovers, fat loss resumes. You'll lose more fat eating more food.
Q: Can I do keto if I eliminate PUFAs? A: Eliminating PUFAs helps. But low carbs still suppress thyroid. Better: eliminate PUFAs AND eat adequate carbs.
Q: What about cyclical keto (carb refeeds)? A: Better than strict keto. But still suboptimal for most. Consistent moderate carbs work better for thyroid function.
This isn't medical advice. Monitor your health markers and work with a practitioner.