Is it dangerous to start a ketogenic diet during pregnancy?


Is it dangerous to start a ketogenic diet during pregnancy? Is ‘keto bleeding’ a thing – and why does it occur in that case? And can keto cause delayed periods?

Get the answer to these questions in this week’s Q&A with the fertility specialist Dr. Fox:

Is it harmful to start keto while pregnant?

Is it dangerous to start a ketogenic diet during pregnancy?


Dr. Fox:

Simple answer = No.

The first week one experiences drug withdrawal from carbohydrates (“keto flu”) which are basically drugs that we ingest in large quantities in our diet. It would then be similar to withdrawal from caffeine for example in pregnancy or cigarette smoking, both of which would be supported by all physicians.

Once you are one week out on the diet, you will be on the best diet possible for pregnancy all the way around for you and the baby. Remember, it is now believed that signals from mother to fetus trigger the insulin resistance system with metabolic syndrome. The signal is undoubtedly related to maternal nutrition.

Learn more: Is low carb and keto safe during pregnancy?

Is “keto bleeding” real?

Dear Dr. Fox,

I’m planning to start LCHF this week, but I have a concern based on what I’ve been reading in several keto discussion forums: many women complain of experiencing “keto bleeding” when they start the diet, which they describe as heavy, persistent spotting, short cycles, and long, heavy periods. The explanation many give — I couldn’t vouch for their medical credentials, but for what it’s worth — is that estrogen stored in fat, and as fat is burned it is released into the system, causing heavy, frequent bleeding, spotting, and so forth.

I am concerned because, at 36, I already suffer from very heavy periods lasting for 7-12 days of my 20-25 day cycle, for which my gynecologist prescribes tranexamic acid. I have struggled with anaemia since I was pregnant with my first child ten years ago. This was controlled with high-dose iron supplements for several years, but I can no longer tolerate them, gastrically. As such, I don’t know how I would cope with heavier or more frequent bleeding, if this is indeed a possible side effect of keto.

I have been told repeatedly that my heavy periods are due to my weight (At 5’5” or 165 cm and 195 lbs or 88 kg I am hoping to lose 50-70 lbs or 23-32 kg). Prior to having children I lost weight easily simply by slightly restricting calories, and had a very regular, manageable cycle. After spending eight uninterrupted years pregnant and/or breastfeeding, I have failed to lose weight on any regime and bleed horrendously.

Having a strong family history of both uterine fibroids and hypothyroidism, I have had both these possibilities checked out. I am told I only have a few very small fibroids, and my T4 is within normal range as the UK guidelines read. The endocrinologist saw no call for further testing, telling me I was “just fat, and possibly peri-menopausal.” (He also said, and I quote “I suppose there could be a female hormone issue, but the fact is we don’t understand how they work, and anyone who says he does is no better than a witch doctor.” This was an endocrinologist.)

Because I have been concerned about my weight gain and inability to lose it despite a healthy diet, discipline and perseverence, my GP checked all my metabolic markers, and found everything (blood glucose, cholesterol, liver function, etc.) to be extremely healthy.

I give this longer history only on the off chance you think there is something else I should ask my doctor to investigate, but mostly I am concerned about the possibility of heavier bleeding on keto, given the issues I already struggle with.

Many thanks,

Dr. Fox:

Wow, can’t believe the doctor’s response. Unfortunately here in the US very few physicians really get hormones either. I will use your history to theorize what is going on for you but remember, this is only a guess given information provided. First, fibroids are highly correlated with endometriosis and adenomyosis, so the increased bleeding most likely is working through an adenomyosis mechanism.

Adenomyosis is endometriosis of the muscle wall of the uterus. In my experience, for endo patients with painful periods, the pain gets better on LCHF nutrition. Bleeding doesn’t seem to change much. Estrogen could be increased with the diet, however, due to the relief of what I term nutritional stress. This stress suppresses estrogen and when relieved the estrogen returns to normal. This might result in more bleeding. It is a double edged sword. On the one hand, you need estrogen more normal to lose weight and have healthy metabolism, but in the face of adenomyosis, bleeding may increase under those circumstances. You would essentially be experiencing what you would have otherwise known, without the nutritional stress.

I would never suggest stopping the diet for this, rather seeking help with the bleeding. Maybe endometrial ablation etc. There could be other reasons for the bleeding as well. Remember too that women with problems are going to talk on the internet about them in great detail, but the 1000’s of women who are doing well are happy and relatively silent.

Delayed periods on keto

Hi Dr. Fox,

I started keto in the month of March and I have lost 10 kilos (22 lbs) since then. I am really happy with the weight loss and I am fully dedicated to the making it a lifestyle. However in the last two months I have had one problem and that is with my periods.

Last month it was late by three days and this month its already four days late and I still haven’t got them. My periods have been regular all my life. I am 34 years old. I have an active sex life however I do not ever have unprotected sex and my partner and I are very careful.

Please help,

Dr. Fox:

Cycle delays are almost always due to stress. It is possible that beginning the diet and withdrawing from carbohydrates which is like withdrawing from a drug could have caused enough stress to affect your cycles. The diet, however, makes people’s cycles more normal from a physiological standpoint. Other than the above, I would not blame the diet for changes in your cycle.

More questions and answers

Questions and answers about low carb

Read all earlier questions and answers to Dr. Fox – and ask your own! – here:

Ask Dr. Fox about nutrition, low carb and fertility – for members (free trial available)

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