Carbs, insulin, and infertility, oh my!

Hey again! In order to officially get my degree, I had to defend the internship I did at a fertility clinic by writing a brief summary of a few studies. The head endocrinologist at the fertility clinic prescribed his patients the EZ diet, which he designed. I wrote all about the diet here, in my post titled The Key To Weight Loss. I am posting my paper defending and explaining the diet, in case anyone out there is a nutrition geek, or simply interested.

The Glycemic Index is by now a well-known quality of foods to take into consideration when making dietary choices. It has been assumed that high GI foods necessarily lead to a great insulin response, due to the increased blood sugar levels. However, some high GI foods are not especially insulinemic, while other lower GI foods actually have a greater insulin response. The EZ diet was designed to minimize the secretion of insulin in the body. The diet is based on studies on foods that determine their score on the Insulin Index, instead of the Glycemic Index. Insulinemic foods are limited while low insulin inducing foods are okay, which makes the diet a lower carbohydrate diet, as well as more limited, than your typical American diet. It is fairly similar to the Paleolithic diet, however it is less limited in food options and also features various diet phases of strictness.  Slabber’s study was on a group of individuals divided into two groups. Half were on a restricted calorie diet and the other half were on a restricted calorie AND low insulin response diet. Both groups lost weight, however the low insulin response dieters lost more. Both groups also had decreased fasting plasma insulin levels, but the drop was much greater in the low insulin response dieters. Therefore, a low insulin response diet is superior for weight loss and reducing plasma insulin levels than conventionally balanced, restricted calorie diets.

But why do plasma insulin levels matter?

The definition of obesity is being 35 pounds overweight. Over a third of America is obese, and an additional third is overweight. The female reproductive system is effected both by the severity of the overweight status and the distribution of the body fat, with abdominal fat being the most detrimental. Some obese women have insulin resistance, hyperinsulinemia, increased androgen levels, altered gonadotropin secretion, increased IGF1, and several other changes to the neuroregulation of the hypothalamic-pituitary-gonadal axis. The mechanism that explains the connection between being overweight and hyperandrogenism (which can lead to infertility) is controversial, but a possible mechanism is discussed below. The purpose of the diet previously examined was to decrease plasma insulin levels. This is because the typical American diet is high carb and high sugar, leading to many insulin spikes throughout the day and an increase in insulin overall. Insulin is molecularly similar to Insulin-Like Growth Factor 1, and thus can bind IGF1 receptors. When insulin or IGF1 bind these receptors, there is an increase in androgen production and stromal cell proliferation. Increased insulin also decreases hepatic production of IGF1 binding proteins, which serve the purpose of decreasing IGF1 action in the body (and thus would prevent the over-production of androgens). Decreasing insulin (often by losing weight and/or restricting certain carbohydrates) has been shown in several studies to decrease circulating androgen levels. Data is also accumulating that even women whom do not have excess fat but do have hyperinsulinemia (possibly due to a high carb or sugar diet) and hyperandrogenemia will have disturbed ovarian function.

So why do elevated androgens decrease fertility?

Willis et al. demonstrated that insulin increases LH action on granulosa cells, which will cause an increase in estrogen production and inhibit the growth and maturation of developing follicles. If the follicles cannot mature, the woman will not have a functioning reproductive system, and pregnancy will not be possible.

To sum up: excessive carbohydrate/insulinemic diet –> increased insulin secretion –> increased action of insulin on IGF1 receptors –>  increased androgens –> inhibition of follicle maturation –>  fertility problems

NOTE: Carbohydrates are necessary for fertility. The EZ Diet (and myself) do not mean to imply that women should not eat carbohydrates. What is important is the source and the amount of carbohydrates in the diet!

7 thoughts on “Carbs, insulin, and infertility, oh my!

    1. I think that really depends on the person, but there are probably many studies/websites/etc that will give you definitive answers. All different Im sure.


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