Is low carb safe during pregnancy?


Is low carb safe during pregnancy?

Get the answer to this and other questions – are the benefits of LCHF different from women with PCOS who are thin, and women with PCOS who are obese? – in this week’s Q&A with the fertility specialist Dr. Fox:

Is it safe for pregnant women to eat a low-carb high-fat diet?

If a pregnant women is having adequate caloric intake and nutrition, does low carb have a negative effect on growth and development or the fetus?


Dr. Fox:

This is a great question. Although there are few, if any, good studies on this subject, we feel this is a good diet for pregnancy. We recommend it to our patients and have had many success stories avoiding large weight gain, nausea in pregnancy, pregnancy induced hypertension, and gestational diabetes that had been experienced by those individuals in former pregnancies. Several of our staff members have engaged LCHF during their pregnancies also with great outcome. Lastly, for the cave women, north of Atlanta, Georgia or so, where did she find significant carbs between Labor day and Memorial day??

The other huge pregnancy complication, death during childbirth was very common before modern medicine and the advent of cesarean section. Carbs create big babies that create trouble for vaginal delivery. I have to believe that we didn’t lose 20 – 30% of cave women in childbirth. There aren’t many mother/baby in pelvis archaeological finds on record. We certainly don’t see that in any wild animal populations.

If ketosis were bad for pregnancy, we would not be here now. Sadly, so many of the ?’s we all have about ketotic diet have not been studied in science really and it makes everyone uncomfortable with the approach since we live in such a factual scientific world. Alternatively, the high carbohydrate diet was never studied either, and certainly there is great evidence to suggest that it is extremely harmful yet as a population there has been little outcry to explore that further. It’s very hard to change what is perceived as normal.

Do you recommend zero carb?

In some of your videos, I’ve heard you say “as close to zero carb as possible”. I did an all meat (ribeye, ground beef, and eggs) diet for six weeks and loved it, and was wondering if that’s something you’d recommend for someone trying to get pregnant (after failed IVF).


Dr. Fox:

Maybe I should qualify that. Our recommendation is high fat, modest protein (correct amount for weight, 1.2-1.7 g/kg ideal body weight) and non-starchy vegetables. If you eat vegetables, you will get some carbs.

In my experience, unless you are in a severe insulin function category, you can tolerate non-starchy vegetables. The further north of BMI 40 you get, the fewer vegetable carbs you could tolerate. So if you don’t fit the worst case scenario, we tell patients for normal servings of one or two vegetables per meal, they can ignore those carbs. The zero would apply to all other foods. In reality this sets the threshold under 20gms per day that everyone agrees produces solid ketosis.
Hope that helps.

Are the benefits of an LCHF diet the same in lean women with PCOS as they are for obese women with PCOS?

I know that a LCHF diet doubles the success rates for your patients – is that statistic true for both lean AND obese patients or only for your patients that are overweight? I can’t find very many studies looking at the effect of an LCHF diet on lean women with PCOS and how it affects their chances of becoming pregnant.


Dr. Fox:

Great question, Erin. There are no real studies in this area and really no good studies in the obese population either. Most obese studies focus on weight loss only and not LCHF or insulin reduction. There are several complicated aspects to this answer. The answer is mostly yes, the two are equivalent but for different reasons. You should think of insulin resistance as a spectrum of insulin function from perfectly normal to worst case scenario. Normal insulin function people can eat carbs and not gain weight and the worst insulin function group will be the most overweight group. Even the lean group begins to gain with age in most cases. Differences exist though in food intake so these findings do vary somewhat. Carbohydrates should be seen as a toxin and the greater the lifetime dose the greater the adverse effect (in this case obesity).

Lean women with “PCOS” are a very mixed group. It is my opinion most women labelled Lean PCOS are not true PCOS but suffer from hypothalamic (stress effect) dysfunction which mimics PCOS in many ways: Testosterone is slightly elevated, acne is present, excessive hair growth is less common, the ovaries have a dramatic “PCOS appearance” on ultrasound, and cycle length can be off up to 40 day intervals, but when tested for insulin resistance are found to be normal. These patients often have no family history of diabetes and longevity is common. Other lean patients do have family history of diabetes and will demonstrate insulin elevation at a fairly low level and therefore have both abnormalities, hypothalamic dysfunction and insulin resistance.

Back to your question: both pure hypothalamic patients and the mixed dysfunction group benefit from LCHF for fertility. Thin women seem more susceptible to hypoglycemia. Therefore, carbs in this group produce dramatic hypoglycemia compared to the obese group. This effect sends a life threatening stress signal to the brain that stimulates cortisol (adrenal) release, significantly reduces FSH and LH the ovarian stimulation hormones, and lowers the metabolic rate through a subtle thyroid mechanism. This change in FSH and LH results in low estrogen and can cause numerous physical and mental effects. All of these stress effect mechanisms can and do cause infertility. Most of the testosterone elevation in these patients seems to come from the adrenal gland. So in summary, LCHF dramatically reduces the stress signals to the brain which are the hallmark of the hypothalamic and hypothalamic/PCOS mix patient.

I know that is a long answer but it needs to be carefully addressed. Our specialty recognizes only the severe hypothalamic patient as abnormal where cycles have completely stopped (amenorrhea) such as in women who are extreme aerobic exercisers (marathon’s etc) and anorexics with severe weight loss. Aside from these women, there are millions of affected women who engage in physiologically stressful behaviors, one of which is the high-carb diet in lean individuals. All of my comments are based on personal patient observation and the application of sound endocrine physiology to these observations since there is no available literature on this subject.

Hope this helps.

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