Are the benefits of a 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 a LCHF diet on lean women with PCOS and how it affects their chances of becoming pregnant.

Dr. Fox’s Answer:

There are no real studies in this area and really not 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 extremely susceptible to hypoglycemia. Therefore, carbs in this group produce dramatic hypoglycemia compared to the obese group. This effect sends a very severe 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.

Michael D. Fox, MD
Jacksonville Center
Reproductive Medicine