The Gut-Brain-Libido Axis

"Science is like sex: sometimes something useful comes out, but that is not the reason we are doing it." —Richard Feynman

We tend to think of ourselves as philosophical creatures, but from an evolutionary perspective, we are basically gonads with supporting organs. Thus, seven billion people swarm the Earth. As Darwin might have said, it’s all about the sex.

Surprisingly, animals need microbial facilitators in their sexual conquest. We may think we own the planet, but we are transient interlopers in a largely microbial world. Since most of these tiny creatures perceive us as lunch, we need to protect ourselves. That is the job of our immune system, but for all of its marvelous ability to adapt to new threats, microbes can run circles around our fortifications.

That is why, millennia ago, we recruited our own microbes to act as our first line of defense. It takes a microbe to fight a microbe.

In return for a continuous feast and a warm spot to reproduce, our homegrown microbes dutifully stab, poison, starve, or eat pathogens who foolishly enter our shared lair. A well-curated collection of microbes, called the microbiome, can spell the difference between good health and bad.

The body under stress

Our body has a tripwire that snaps under stress, causing us to switch to panic mode. It gathers all our energy to fight or flee a potential threat. It draws that energy from other bodily systems, including the immune system. It also pulls from the libido, the name Freud gave to the sex drive. When you are running from a tiger, there’s no time for lust.

For those beset by demanding bosses or an unjust world, the stress puts a real damper on our love lives. This stress likely plays a role in our declining birth rates.

But our microbiome also plays a role. When it gets unbalanced (called dysbiosis), it can create a stress of its own, pretty much indistinguishable from external stress.

The microbiome can pull other strings as well. Our sex hormones, headlined by testosterone and estrogen, have a strange relationship to gut microbes. Once in circulation, hormones need to be controlled, or they can drive us mad. That job falls partly to the liver, which places hormones into molecular cages made of sugars and proteins in a process called conjugation. Thus packaged and inactivated, the liver slips the hormones into bile, which it sends to the digestive system for excretion.

But certain microbes in our gut like to snack on these cages, liberating the hormones. That’s how microbes act as a source of human sex hormones. A healthy microbiome produces optimal hormone levels, while a dysbiotic microbiome disrupts the hormonal balance, leading to a loss of libido.

The gut-brain axis

Research by John Cryan, Ted Dinan, and others has shown that microbes can affect our sex drive via the gut-brain axis in various other ways.

On the negative side, some microbes produce toxins that induce anxiety and depression. This can be exacerbated by a leaky gut. Systemic inflammation can impair blood flow and dampen the brain circuits involved in arousal and sexual performance.

On the positive side, beneficial gut microbes can produce neurotransmitters—the chemicals that nerve cells use to communicate—including serotonin and dopamine, which are the targets of antidepressants. These neurotransmitters may communicate with our brain via cells in the gut called neuropods.

Depressed people are not, in general, thinking about sex. In fact, a core feature of depression is anhedonia: an absence of enjoyment, interest, and sexual motivation.

Cryan and Dinan have shown that certain microbes can improve anhedonia and mood in general. They coined the term psychobiotic to refer to these microbes as well as the prebiotic foods they like. By tweaking stress levels, sex hormones, and neurotransmitters, microbes play an outsized role in erectile dysfunction and libido.

If the thought of trillions of tiny microbes controlling your sex life gives you goosebumps, take heart. You may not have much control over your stressful environment, but you have an amazing leverage over your gut microbes.

You’re in charge of your gut

According to a recent review by Italian researchers Giuseppe Marano, Marianna Mazza, and colleagues, “Lifestyle factors, including diet, stress, and antibiotic use, can modulate the gut microbiota and, consequently, sexual health outcomes.”

You can tip the balance of your gut microbes to be healthier and sexier with some specific changes. These are not shocking interventions: exercise more, sleep better, and eat your veggies.

The veggies with the greatest impact are the ones with fiber and polyphenols, which are the preferred food for psychobiotic gut microbes. These include colorful foods like beets and berries, as well as fibrous foods like lentils, artichokes, onions, and beans.

There are important caveats here. These foods are potent, and if you are accustomed to a lot of processed food, you may be in for a shock. Start slowly, or you may get gassy and bloated, something that makes a lot of people jump ship prematurely. Also, if you are having a flare-up of irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD), wait for symptoms to resolve, or you could exacerbate the situation. Talk to your doctor about diet changes if you have intestinal issues.

Boosting your good microbes can make you feel better and boost your libido. Once you get sexier, you’ll want everyone else to be sexier too, so pass this post around.

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