Fact-checked by Dr. Anthony Gustin, DC, MS.
Written by Joanna Cailas
The unfortunate part is that if women rely on hearsay and don’t source better information about ketosis and their hormones, they lose out on the benefits of ketosis, especially those who suffer from PCOS, endometriosis, and uterine fibroids. Women with these conditions can benefit significantly from the ketogenic diet. 
In this post we’ll discuss the ketogenic diet’s impact on your thyroid and the HPA axis, then look at ways to evaluate your hormones, how you feel, and what adjustments to make.
The Ketogenic Diet and Your Thyroid
Is ketosis bad for your thyroid? No. Let’s break it down:
- It’s true that low-carb diets (like the ketogenic diet) and calorie restriction lowers T3, the thyroid marker hormone.  
- T3 make your cells use more energy. Because of its function, scientists have hypothesized that “a reduction in T3 hormone may increase lifespan by conserving energy and reducing free-radical production.” 
- Together with T4, these hormones regulate your metabolism, heart rate and body temperature. Most of T3 binds to protein and some free T3 circulates in your blood.
But a lowered T3 doesn’t mean you get thyroid dysfunction or hypothyroidism.
Hypothyroidism is often a case of high levels of TSH (thyroid stimulating hormone) and low levels of free T4. The pituitary gland tries to get your thyroid gland to produce T4: high levels of TSH. But the thyroid isn’t responding: low levels of T4.
When T3 is reduced, the thyroid is called “euthyroid.” A normal thyroid. For a more in-depth look at what a low-carb diet does to T3, T4 and TSH levels, read Dr. Anthony’s article on ketosis and women’s hormones.
Ketosis, the HPA Axis, and Cortisol
The HPA axis is the triumvirate of hormonal production: the hypothalamus secretes hormones and talks to the pituitary and adrenal glands into doing their jobs toward producing those hormones.
- No, ketosis does NOT mess up your HPA axis. The opposite is true: the genuinely ketogenic diet may actually benefit the HPA axis; it helps with better hypothalamic stimulation. 
- There is no evidence that a ketogenic diet affects the HPA pathway in any way. Data shows that ketone signaling uses a different (and probably more efficient) pathway. 
- Hypothalamic neuropeptides, superior mechanisms for hypothalamic stimulation, are clearly extremely elevated in a ketogenic diet. Studies show that ketones cross the blood brain barrier and act as signaling molecules on hypothalamic neuropeptides. 
The ketogenic diet and cortisol:
Cortisol is the notorious stress hormone but it starts out innocently. When you’re under stress, cortisol taps into protein stores and produces glucose for your body to use to flee or fight the stress. Good thing, right?
- But consistently high cortisol levels means consistently high stress levels, and your body and brain starts to tire.
- All that extra glucose means elevated blood sugar, which leads to all sorts of problems.
Because the ketogenic diet leaves the HPA axis unaltered or potentially improved, then cortisol–produced within the adrenal gland– is fine. In fact, cortisol levels are low for those in ketosis,  or completely unaffected. 
If you feel particularly bad, here are a few points to consider:
Are You Overtraining?
Think of your priorities. Is it performance with your HIIT 3+ times a week? Or achieving ketosis?
If you go for both, you are overtraining. This may lead to cortisol levels shooting up (your body is stressed from what you’re putting it through) and other hormonal problems. Overtraining is the root cause of it,  not ketosis. A ketogenic diet may not be the best match for rigorous training goals.
Here are a few symptoms of cortisol elevation  and other hormonal issues caused by overtraining: 
Are You In Ketosis?
You are in ketosis when AND ONLY WHEN you meet this condition: your body is breaking down fat into ketones as an energy source. How do you know this? By testing your ketone levels. Pee sticks and breath meters are not accurate because ketones are in your blood.
You use a blood meter like the one used to measure blood glucose. Prick your finger for a drop of blood and set the machine to tell you your BHB (beta-hydroxybutyrate) levels. In ketosis, your measurement would be consistently above 0.5, without using exogenous ketones.
Eating high-fat and low-carb but not in keto
High fat and low carb diets don’t feel good.
If you’re on such a diet because you’re starting keto, you may feel terrible before you achieve ketosis. This is called the keto flu. Your body is changing gears and protesting a little. Do things properly and you may avoid the keto flu.
There’s no comparison between ketosis and a ‘low-carb/high fat but non-ketogenic’ diet .
The ketogenic diet regulates energy in an entirely different way  and breaks through the blood-brain barrier, which means your brain gets fed, and feeding your brain means improved mental acuity and physical energy. You feel great, like you can do anything!
Are You Eating Enough?
Stick around long enough and you’ll read/hear stories about how being in ketosis helps so much with intermittent fasting (IF). People don’t get hungry or crave food like they used to and have no trouble following their fasting schedule. 
But make no mistake, keto-ers who do IF for its benefits are fastidious about measuring their calories and eating enough when they eat. Because calorie restriction only makes you feel bad, and is proven to affect hormones negatively, especially in women.   In this case, it’s not ketosis making you feel bad. It’s your starvation.
Measure your ketones, measure your food intake, and make sure it’s adequate to the demands of your day.
Are Your Hormones Out of Whack Already?
If your periods have always been bad, or if you have chronic pain you can’t explain (back ache, severe headaches), you may have hormonal imbalance, which needs correction and consultation with your doctor before you do something drastic as undertaking the ketogenic diet. If already in ketosis, SEE YOUR DOCTOR if you’re concerned about any drastic changes like amenorrhea (lack of menstruation), clotting, pain, etc.
Keto and your periods: what to expect (and not to expect)
- You may get your period back after having experienced an irregular flow most of your life
- If you’ve been in birth control, and stopped or removed the device, or a natural amenorrhea (for athletes and breastfeeding mothers), your period may go back with a heavy flow to start.
- You may get heavier than usual bleeding, lasting for more days than before. Once your body adjusts and compensates for all the changes in estrogen levels and body fat storage and use, everything would go back to normal, or better than before
- Ketosis doesn’t cure bloating. While most other PMS symptoms get better or get done (back ache, cramps, etc), bloating remains. It’s due to the massive surge of estrogen in that part of your cycle.
- Hormones affect your insulin sensitivity. Blood glucose surging or dropping is normal. After your period, it should get back to normal.
- If you’re hungry, eat. After ovulation, your body prepares to pump out estrogen and progesterone—which can cause hunger. Go for keto-friendly chocolate, keto mug cakes, fat bombs, or go take home the bacon or the steak.
Check out this article from Wicked Stuffed for tips on keto for women, especially for that time of the month.
Are You Stressed?
Stress can lead to hormonal problems, especially in women, and managing stress may help solve those problems.  
Instead of rigorous training, aim for light movement like yoga, and try meditating, walking and journaling to take control your anxiety and stress levels. When your stress is persistent enough, you need medical intervention.
To Sum It Up:
The ketogenic diet, in and of itself, doesn’t affect women’s hormones in a negative way.
Hormonal imbalance has other root causes:
- Pre-existing hormonal imbalance (not caused by keto)
- Hypo or hyperthyroidism (also not caused by keto)
- Not eating enough (you are starving)
These other causes need to be ruled out—and treated—before you and your doctor can conclude/diagnose a bad experience with ketosis—if you have actually been in ketosis.
Measure your ketones and make sure your caloric intake matches the physical demands you put yourself through. Go after healthy fitness goals and keep your stress levels down.
Wondering about how keto has affected other women when it comes to their periods, or in their senior years, during/after menopause? Lots of heartening answers in Ketogenic Forums and also in this Reddit thread. You would also find support and discussions in our Perfect Keto Community. For information about ketosis and pregnancy, go here.