A patient named Barbara bounded into my office. She threw herself into a chair, and looked at me with eyes of terror, guilt and shame. I knew from her countenance that it was confession time. She launched into her story, retelling an all-too-familiar tale: She hadn’t stuck with her anti-inflammatory diet. Her food cravings, she explained, were out-of-control, and she was miserable. Her weight was exploding, her abdomen was bloated and her head ached. But perhaps most importantly, she was depressed, anxious and felt like a failure….
“I can’t do this horrible diet!! I’m sooooo miserable, but I must have my comfort foods!!”
We’d been down this road together many times before. I was feeling discouraged right along with her.
Exasperated, I blurted out, “Who am I speaking with — Barbara, or her gut bugs?”
The question momentarily silenced both of us. It was an epiphany. For Barbara and for me. Here was this lovely young woman, so eager to get well, but repeatedly failing in her attempts. Her short-lived moments of healthy eating demonstrated that the rewards would be high with regard to symptom resolution; but she so often plunged to epic lows as she gave in to the “voices” that whispered insistently, “Donuts, pizzzzzza, fried chicken….”
At that moment, sitting in a chair in my office, Barbara no longer appeared to me as Barbara. Rather, I was now speaking with a teeming, nefarious gut microbiome, out for its own selfish survival, host be damned! Petulant and irrational, these critters allowed for no negotiation. It was the puppet master; Barbara, its unwitting marionette….
We’ve known for years that our gut bugs — all 100+ trillion of them — profoundly influence human physiology. Imbalances in our microbiome are associated with autoimmune disease, diabetes, heart disease, allergic disease and even obesity.
We’ve also known that the inflammation generated by an imbalanced microbiome can influence our mood; that is, our gut bugs can produce (or influence the production of) inflammatory cytokines that increase excitotoxic neurotransmitter release, deplete our feel-good neurotransmitters and make us feel lousy.
And those of us who treat patients have observed for a long time now that food cravings appear to be influenced by these same bugs: We are what our gut bugs eat; and when the ugly bugs are gunning for control, the outcome isn’t pretty. Conversely, when the diet is clean and balanced, cravings resolve or are minimal, health is restored and psychological well-being is established.
Being a bit of a research junkie (influence by my microbiome?) I have been looking for a satisfying scientific explanation for what we see clinically. Finally, such a paper has been written — published this month in the journal Bioessays, Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms by Alcock, Maley and Aktipis. This article delivers the best collection of arguments for why ‘we are what our gut bugs eat’ that I’ve seen yet.
Evolutionary conflict between host and microbes leads to host manipulation. This makes good sense. Diets as actions of will-power fail time and again. Counting calories doesn’t work. Gut bugs appear to be able to manipulate host eating behavior in ways that promote their fitness and survival at the expense of host fitness.
Microbial genes outnumber ours 100 to 1, giving bugs the clear numbers advantage. A larger, but less diverse, microbial population (often seen in disease states) has a powerful capacity for host manipulation by virtue of its ability to produce higher quantities of host behavior-altering neuroactive compounds. Further, microbes may engage in large-scale host manipulation/coordination through quorum sensing.
Of note:
- Microbes can generate hunger- (or satiety-) inducing hormones structurally similar to ghrelin and leptin.
- Negative mood, induced by microbial-generated toxins, has been shown to increase eating in an animal model.
- Virulence toxins are produced by microbes when host nutrients are low, influence eating.
- Taste receptors, altered by microbes, have been shown to alter eating behavior.
- Enteric receptors — including cannabinoid and opioid receptors — respond to microbes.
- Microbes produce genes for human neurotransmitters, generating far more dopamine, norepinephrine and serotonin than their human hosts.
For Barbara, the good news: Hang in with the dietary changes, and the cravings WILL stop.
We can, fortunately, change the make-up and behavior of our microbiome by altering our eating. And it can happen quite quickly. Thus, moving away from a damaging diet — and sticking with it just long enough — can reduce cravings and restore microbial diversity. Further, altering the microbiome through prebiotics, probiotics, fecal transplant and (perhaps) antibiotics may be realistic and potent interventions for cravings, mood, obesity and unhealthy eating.
The players we want in abundance:
- The commensal microbiome responds to yoga and meditation, which have, in turn, been shown to increase will-power. (Could this be mediated by a microbiome shift?)
- A balanced microbiome can increase satiety and good mood by generating leptin-type compounds and (lots) of dopamine. (Think about this: Could a probiotic formula treat Parkinson disease?)
- Lactobacillus species has been shown to reduce anxiety and hunger-inducing hormones.
- Certain lactobacillus and Bifidobacterium species inhibited weight gain and insulin resistance and improved glucose tolerance.
- B infantis raises serum tryptophan.
- B breve inhibited weight gain in mice.
- L rhamnosus GG and B lactis were associated with reduced weight gain in post-partum women.
- Lactic acid producing bacteria increase the anti-anxiety neurotransmitter GABA.
- L rhamnosus reduced stress-induced corticosterone and increased stress resilience (mice).
- L. helveticus and B. longum alleviated psychological distress (mice).
A potent well-designed cocktail of pre- and probiotics may be exactly what Barbara needs to move her through the craving stage just long enough to resume being in the driver’s seat, or at least in a comfortable passenger’s seat, with a happy microbiome.
