Metabolism controls fertility
Summary
Metabolic disorders are the most common reason for infertility.
Cold water therapy resolves insulin resistance, improves sexual function, and increases fertility in both women and men.
Avoid heat exposure (e.g., sauna) when seeking to conceive. Women can benefit from cold water therapy during pregnancy, but should wait until after childbirth to sauna.
Ice baths sex hormones
I've written several articles on the salubrious effects of deliberate cold exposure for sexual and reproductive health. For example, you might be surprised to learn that deliberate Cold Exposure During Pregnancy is associated with better birth outcomes and that sauna is not.
On the other hand, if you're a regular reader of this journal, then you probably heard about when Joe Rogan read excerpts from 'What happened to my testosterone..., on his podcast with David Goggins. When that became popular, I got a bunch of requests from men who wanted to know how I accidentally boosted my T levels to over 1100 ng/dL by exercising after my ice bath instead of before. (It's called precooling, and when you try it, you're going to notice a big stamina and performance boost).
In Couples Cold Therapy I wrote about the correspondence between hormones and neurotransmitters generated by the ice bath and the brain chemistry of lust, romance, and love. You'd think I'd pretty much covered everything essential about ice baths and sex.
Nonetheless, when Prof. Ben Bikman posted a new study on low carbohydrate diets and sexual performance in men, I realized that it was time to do a more comprehensive article on a consistent theme: metabolism and reproductive health.
Fertility Crisis
Births rates in the US have plummeted in the last decade and a half. After peaking at about 68 births per 1000 women (ages 15-44) in early 2007, the natality rate has fallen to less than 57 in late 2022 (CDC 2022). In fact, the birth rate has now fallen below the death rate. If not for immigration, the American population would be shrinking -- like many other industrialized countries (including Japan, China, Russia, Poland, and Greece).
There are several reasons for it.
One explanation is that women are waiting longer to have children or prefer smaller families to allow themselves to prioritize expanding career opportunities. Given the precipitous decline in teenage pregnancy, more careful family planning is no doubt a factor -- but it doesn't explain the anguish many couples feel after several unsuccessful years of trying to have a child.
When we look closer at the health statistics, there are several reasons to believe that the fertility of couples in the industrialized world is in steady decline, regardless of motivation. For example, sperm counts declined by more than 50% between 1973 and 2018 (Levine et al. 2022). Testosterone levels, which are associated with libido and sexual function in both men and women, have been declining, too -- even among young men. In adolescent and young adult males, average testosterone levels have dropped from over 600 ng/dL in 2000 to 450 ng/dL in 2016 (Kahl 2020).
Trends are no better for women. The leading cause of infertility in women under the age of 35 is polycystic ovary syndrome (PCOS) -- a condition in which fluid-filled sacs form in close proximity to the ovaries and interfere with ovarian function.
Both low testosterone in men and PCOS in women are associated with high body mass index, obesity, and insulin resistance. In other words, metabolism.
Metabolic fertility
Sexual function and reproduction is metabolically demanding. Therefore, metabolic disorders disrupt sexual and reproductive functions. There are two types of irregularities that can interfere with fecundity: 1) starvation, and 2) overfeeding.
Cold therapy is unlikely to be helpful in cases of starvation or nutrient deficiencies. Because the cold is metabolically and nutritionally demanding, an ice bath is a better remedy for disorders of overfeeding (such as insulin resistance resulting from excess carbohydrate intake). Nonetheless, I'll review some of the problems that caloric and nutritional deficit present when planning for parenthood.
Starvation
Men
A healthy man can produce over 100 million sperm a day. Although the number sounds impressive, the total volume of synthesized material is small. Nonetheless, under caloric deficit, the male body compensates by conserving metabolic resources. Testosterone levels drop first, which can impair sexual function. Continued starvation can result in reduced sperm production.
In the modern, industrialized world, starvation among men planning families is rare. Micronutritional deficiencies resulting from a poor quality diet is more likely. For example, deficiencies in zinc and/or folate can result in disorders of the testes (Cheah & Yang 2011) and simultaneous supplementation has successfully treated some subfertile men (Irani et al. 2017).
Women
The metabolic requirements of conception, pregnancy, and breastfeeding for women are enormous, for reasons that should be obvious. Consequently, extended caloric deficit and low body fat composition are associated with reduced female fertility. In the industrialized world, there are two principal conditions under which these conditions can persist:
anorexia nervosa, or other eating disorders, and
extreme exercise or physical training.
In either case, low levels of body fat can result in hormonal disturbances that interrupt ovulation and cause menstrual dysfunction. The case of anorexia is particularly tragic, given mortality among the suffering is higher than any other mental disorder and recovery rates are poor (Arcelus et al. 2011, van Eeden et al. 2021).
Anorexia Nervosa (AN) is a complex psychosomatic eating disorder, primarily affecting adolescent girls and young women. The physical signs and symptoms of AN, such as extreme weight loss, fatigue, dizziness, or fainting, are related to starvation. They also include emotional and behavioral issues, like severely restricting food intake, exercising excessively, frequently skipping meals or refusing to eat, and an incorrect perception of body weight in parallel with an extreme fear of gaining weight. - Boutari et al. 2020
Treatments for anorexia typically address the acute dangers of starvation without resolving the underlying psychological disorders. As a consequence, about 20% of survivors fail to show any lasting improvement (Steinhausen 2002). Recent evidence suggests that the anxiolytic (anxiety-reducing) effects of a ketogenic diet may allow refeeding for anorexics with a diet high in animal fats and protein (Scolnik 2017).
In Ice Bath for Fast Keto, I explained that the fastest way to stimulate production of endogenous ketones is deliberate cold exposure, and how the ketogenic diet has a bad reputation that it doesn't deserve. Nonetheless, ice baths have been abused by anorexics long before they became popular among biohackers (e.g., Smith et al. 1983). One survey found that more than half of respondents with an eating disorder endorsed deliberate cold exposure in some form, as a method to promote fat loss (Reas et al. 2019).
My own findings in Calories and Cold Exposure indicate that, despite the fact that ice baths do stimulate fat-burning metabolism, compensatory metabolic mechanisms make them ineffective for weight loss. Thus, the use of deliberate cold exposure by anorexics, is ineffective, ill-informed, and ill-advised.
Anorexia can co-exist with extreme athletic training. Sports like long-distance running, gymnastics and ballet demand very low body fat composition and put women most at risk for reproductive irregularities due to energetic deficits (Boutari et al. 2020). In these cases, ice baths will do nothing to promote or improve fertility, although women may be using ice to reduce delayed onset muscle soreness from over-training, or manage the inflammation associated with joint overuse.
Overfeeding
Excess carbohydrate and seed oil intake is characteristic of the Standard American Diet (SAD). The metabolic consequences can be disastrous, which brings us back to Bikman's recent Instagram post.
Bikman is best known as the author of Why We Get Sick (Bikman 2020), in which he reveals that insulin resistance accompanies 8 out of the 10 leading causes of death in the US, including: cancer, Alzheimer's, cardiovascular disease, Type 2 diabetes, and obesity.
Insulin is the hormone responsible for moving glucose from the bloodstream into muscle, fat, bone, brain, and every other living cell in our bodies. Once across the cell membrane and inside the cell, mitochondria will convert the energy in the glucose to fuel for exercise, growth, heat production, or increased white fat storage.
The basic mechanisms by which carbohydrates and seed oils contribute to insulin resistance are these:
Chronic excess carbohydrate intake causes cells to resist the effects of insulin, leaving glucose in the bloodstream rather than inside the cell. In this way, insulin resistance protects mitochondria from being overworked, and the damage to mitochondrial DNA that can result. In other words, insulin resistance may be the body's natural attempt to protect mitochondria from the reactive oxygen species that are associated with rapid glucose conversion. However, elevated blood glucose has longer-term negative consequences in practically every other function of the body.
Seed oils (e.g., soybean, cottonseed, peanut, grapeseed, and corn oils) contain higher levels of linoleic fatty acids than do fruit oils (e.g., coconut, olive, and avocado oils) and animal fats. While some linoleic fatty acid is essential for proper human function, the levels in seed oils are far in excess of the body's needs. As a result, the composition of cell membranes, in which fatty acids are an essential component, is altered to reflect the surplus of linoleic acids, at the expense of other fatty acids. This alteration may contribute to insulin resistance by making cell membranes less amenable to glucose transport, further contributing to elevated blood sugars.
A regular practice of ice baths can reverse insulin resistance -- even after it has progressed to its more extreme state called Type 2 diabetes. The principal mechanism is activation of brown fat by exposure to cold.
Brown fat and white fat perform different functions in the body. White fat stores energy in the form of lipid droplets that can be released into the bloodstream during times of energy deficit. In contrast, the purpose of brown fat cells is to consume caloric energy. Brown fat cells, also called brown adipose tissue (BAT), are packed with thousands of extra mitochondria that are activated by the sympathetic division of the autonomic nervous system when thermoreceptors in the skin detect temperatures dropping.
The process of activating brown fat in the cold is called cold thermogenesis, because it causes the white fat cells to release lipids into the blood stream to fuel heat production in the brown fat. Despite extraction of heat from the body via exposure to cold water, active brown fat can help maintain a healthy body temperature. The process of cold thermogenesis clears glucose from the bloodstream, consumes triglycerides, stimulates endogenous ketone production, burns calories, and can continue for hours after completing a cold exposure session.
Human babies are born with copious quantities of brown fat to keep them warm in the cold. As they grow and their muscles mature, they lose that brown fat. Eventually, shivering thermogenesis dominates brown fat thermogenesis. By the age of 40, over 90% of American adults have no detectable brown fat. Nonetheless, cold exposure will stimulate the body to recruit new brown fat, restoring some of the capacity for non-shivering thermogenesis that was lost.
The metabolic benefits of brown fat are profound. Not only does brown fat help to maintain insulin sensitivity, it also secretes hormones that modulate other metabolic functions -- including the thyroid. Loss of brown fat can result in a dysregulated thyroid, including a condition called Hashimoto's hypothyroidism. Restoration of brown fat can resolve Hashimoto's.
Men
The systemic consequences of insulin resistance are damaging to male sexual function and fertility in several ways. For example, the relationship between insulin resistance and erectile dysfunction (ED) is so strong that ED is now considered a clinical marker of insulin resistance (Yao et al. 2013). Moreover, insulin resistance interferes with testicular function and is associated with low testosterone (Rao et al. 2013).
In the new study Bikman cites (Schmitt 2023), a group of Brazilian men (average age about 59 years) suffering from low testosterone and insulin resistance were enrolled in a 3-week clinical trial to test the effects of a low carbohydrate diet on sexual function. Although patient compliance in diet studies is often unreliable, in this case the modified diet allowed up to 30% of total caloric intake from carbohydrates (about 30g per day). While that's a low carbohydrate intake compared to the SAD, it's borderline for people their age who want to remain in ketosis -- depending on their activity levels -- and not difficult to maintain. Diets in the control group were calibrated to provide the same caloric intake.
The results after 3 weeks were remarkable. The low carbohydrate group lost weight, reduced their waist circumference measurements, increased their testosterone levels from an average of 229 ng/dL to 310.7 ng/dL and increased their scores on the International Index of Erectile Function (IIEF-5).
While these men were about my age (I turn 57 in 2023) they began their low-carb diets at testosterone levels much lower than I did. In Prostate Protocol, I describe the ketogenic/ice bath regimen I practiced when I was concerned about my elevated prostate specific antigen (PSA) test.
By using exercise to rewarm after my ice bath, I increased my testosterone levels from about 700 ng/dL to about 1100 ng/dL -- much higher than the levels achieved in the Brazilian study. That helps resolve the question "What benefits would low carb have for men who are not starting out with low T?"
Moreover, when you consider that I was doing ice baths in addition to low carb -- both of which are proven to benefit mitochondria and increase insulin sensitivity -- it may explain why my results were better than the Brazilian cohort on a percentage basis. In other words, you don't have to be suffering from insulin resistance or low T to benefit from a program of ice baths and exercise.
Women
In men, the testes are outside the body because they function better at temperatures slightly below the normal body temperature. However, in women, the ovaries are contained within. As a consequence, the physiology of insulin resistance is different in women than in men.
One of the manifestations of insulin resistance in pre-menopausal women is PCOS. The association between PCOS and metabolic disorders is very strong and women who suffer from PCOS often have other markers typical of insulin resistance, including obesity.
In PCOS, fluid-filled sacs (cysts) form in close proximity to the ovaries and interfere with their proper function, including cessation of ovulation and (ironically) overproduction of testosterone. Few people know that in healthy women, testosterone levels exceed estrogen levels by about a factor of three. Therefore, testosterone is the dominant sex hormone in men and women. In both sexes, deficiency can result in low libido and loss of sexual function.
However, the effects of insulin resistance on testosterone in women can be different than in men. The impingement on the ovaries in PCOS often stimulates overproduction of testosterone, rather than underproduction. (In men, testosterone is produced in the testes In women, testosterone is produced in the ovaries). That explains why some women with PCOS also experience acne and unwanted hair growth.
The resolution of PCOS is found in the metabolism.
When a group of Australian researchers recruited premenopausal women with and without PCOS to participate in a study relating skin temperature to brown fat activation, they concluded that women with PCOS have lower brown fat activity than the control group without PCOS (Shorakae et al. 2019). Those findings are consistent with animal models in which the transplantation of brown fat resolved PCOS in rats (Yuan et al. 2016).
To test whether deliberate cold exposure could ameliorate PCOS by recruiting brown fat to rats, researchers in China housed animals in a thermostatic incubator at 4°C for twenty days. They observed that "cold treatment improved BAT activity," which is to be expected (Ye et al. 2021).
What researchers did not expect was that normal mensuration was restored in 75% of the cold-treated rats, compared to 30% in a control group with PCOS housed at normal temperatures. Moreover, the cold treatment significantly decreased abnormally high testosterone and luteinizing hormone levels. The researchers concluded that "cold treatment can restore ovarian cyclicity and reverse hyperandrogenism" (Ye et al. 2021). Finally, the cold-treated group of female rats experienced twice the rate of successful pregnancies than the PCOS control group.
Ice baths for fertility
Couples seeking to conceive and birth a child would do well to consider the metabolic aspects of sexual function and fertility. In general, it can be said that deliberate cold exposure promotes fertility in men and women eating sufficient protein and low-linoleic fats -- with the important exception that in cases of infertility caused by insufficient body fat or energy deficit, ice baths will be unhelpful.
The principal mechanism by which an ice bath supports sexual health is by activating and recruiting brown fat to correct metabolic disorders, and by modulating aberrant testosterone levels. In men, exercise for rewarming after a 2-4 min cold water immersion session can boost testosterone levels, and may encourage sperm production by cooling the testes. In women, the exercise may be unnecessary.
As I wrote in How to use cold water therapy to boost testosterone, naturally, there is only one study examining the relationship between testosterone and cold exposure in healthy young women. In it, researchers discovered that cold stimulation of just one hand increases testosterone in healthy college undergraduate women, even without exercise (Archey et al. 2019). However, in cases of women with PCOS who already suffer from excess testosterone, cold exposure may have the opposite effect of reducing testosterone levels by resolving PCOS. In other words, an ice bath practice could have a modulating effect on testosterone in women -- reducing it in unhealthy women when it is already too high, and raising it in healthy women who might benefit from the boost.
Heat is a different matter
When seeking to have a child, both men and women should avoid the sauna. Although the health benefits of sauna are well-documented, fertility is not one of them. In men, it reduces sperm production (without impacting testosterone) and in women heat is associated with reduced rates of conception and poorer birth outcomes. After the child is born, sauna is safe for women to use again, and may even promote lactation.
About the Author
Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.