Anyone who has the view that sugar is the devil and insulin is it’s minion, don’t read this as you probably have already made up your mind and think I am in bed with the soda industry down here in the Jungle.
Caring and well meaning Nutritionists or Functional Med Peeps who pound everyone with restrictive diets without context or an exit strategy please pay attention and work to see the endless shades of gray.
Acute or long-term calorie restriction will generally knock down reproductive function in normal weight individuals (not necessarily so in overweight/obese populations).
“Negative energy balance either due to hypophagia or excessive energy expenditure is linked to a suppression of reproductive function and ovarian cyclicity in a variety of species including humans.”
-Silwowska et al. 2014
Leptin is a long-term fuel status hormone secreted by adipose cells. It is thought to have a permissive role in GnRH secretion at the level of the hypothalamus. And pounding energy deprived humans with 50x physiological levels of Leptin only partially restores GnRH and subsequent pituitary hormone secretion. As you might have guessed the story goes much deeper than Leptin as the human body is never that simple.
In this regulatory circuit, we have compounds that no one has ever heard like KISS1, Neurokinin B, gonadotropin-inhibitory hormone, Alarin, and we even have “certain neuronal populations that are capable of sensing metabolic status through changes in circulating glucose levels.” – True et al. 2011
We also have other more known regulatory players like CRH, Cortisol, Ghrelin, Prolactin, NeuroPeptide Y and certain inflammatory cytokines.
But, one hormone that often gets shoved under the rug in our current carbophobic society is Insulin.
“Both pulsatile and surge modes of GnRH secretion are sensitive to metabolic signals and pathological situations which lead to acute and/or chronic hypo- or hyperinsulinemia are frequently coupled with disturbed GnRH/LH pulse and surge release patterns.”
– Silwowska et al. 2014
We also know females are much more sensitive reproductively to drops in carbohydrate consumption.
“GnRH neuron activity and LH pulsatility are actually regulated by brain glucose availability. The adult female human brain oxidizes about 80 g of glucose each day at a continuous rate. This must be provided daily by dietary carbohydrate, because the brain’s rate of energy expenditure can deplete liver glycogen stores in less than a day. Moderate exercise oxidizes as much glucose in an hour.”
-Loucks 2013
Thus, if you are a female who exercises at higher intensities your goal should probably be to get carbohydrates as high as possible without absolutely blowing out glucose variability and overall caloric consumption. Please do not take this out of context and think for a second that I am saying food quality and proper blood glucose regulation are not insanely important. Yet, we should probably educate and lighten up on the PaleoAF with this population because dietary restraint without caloric restriction is related to dysmenorrhea and it is estimated that nine times more women are on a “diet” than men.
How many females do you know who are next level afraid of carbohydrates as a defense mechanism to our current obesogenic food environment?
Low carbohydrate diets can also knock down the HPG axis in men, especially when combined with high-intensity exercise to which they now lack the appropriate fuel to perform. Men do seem to have more leeway than females in this regard, and a lot of the findings are contextual.
Thus, if you are a guy and are using lower carb diets or intermittent fasting, I would highly recommend running your own N of 1 study and collect pre and follow-up data so that you can have a more tactical and individualized approach which may change over time.
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