How microbes hack your cravings

“Food is not rational. Food is culture, habit, craving and identity.” —Jonathan Safran Foer

I have meticulously honed my taste buds for years to appreciate the finer things in life like donuts, cheetos, and pizza. OK, I don’t actually remember choosing them, but I must have, right? Scientists, however, point out that our gut microbes — known as our microbiome — play a major vote in what we crave. How is that possible?

Starting with flies

Flies like yeast for its protein. It’s like filet mignon to them, and they particularly like it when they have been denied protein. So, it was weird to Carlo Ribeiro and his colleagues when they found a group of hungry flies that turned their tiny noses up at yeast. They discovered that these atypical flies had specific microbes that altered their cravings, even though it was potentially bad for their health.

Cravings, it turns out, may be better for gut microbes than for their hosts. At least for flies.

Moving up to mice

After flies, the next best research subjects are mice, and here we have a creepy story. Normally, mice wisely scurry off when they smell cat urine, but there’s a parasite called toxoplasma which alters that behavior. Mice infected with toxoplasma actually get turned on by cat pee: They crave it. As a consequence, they often end up as lunch for a cat, which is nourishing for the cat, essential to the life cycle of toxoplasma, but quite unfortunate for the mouse.

This macabre behavior demonstrates that cravings established by microbes can lead to a swift death. So, for both flies and mice, microbes drive food choices, even if it kills their host.

Humans Too?

Gastric-bypass patients offer a great window into microbial cravings. After a bypass, the microbiome undergoes a major shift. Along with that comes a big change in cravings. People who once kept Snickers in every pocket and drawer may suddenly stop craving sweets. They lose their taste for fatty foods. Amazingly, researchers now suspect that at least some of the success of bypass surgery is due to these changes in cravings, not the decrease in stomach volume.

A similar story exists for GLP-1 drugs.

There’s more. Pregnancy brings about major changes in the mother’s body, including their microbiome. Pregnancy is famous for crazy cravings, and gut microbes may drive some of those behaviors.

So, flies, mice, and humans all have manipulative microbes that can affect eating behavior. That’s more than a little humbling.

The fact is, we are being played. Gut microbes are not our “friends”, they are associates that we share meals with but can turn on us at any moment. If the food runs out, they will be just as happy to digest us.

They each have their own appetite: some microbes crave sugar, others enjoy fat, carbs and fiber. They each have their own method of asking for their favorite meal, using variations on two basic techniques to influence our food choices.

• Microbes can produce toxins that make us feel like crap if we don’t give them what they want.

• Microbes can change our taste buds, increase opioid and cannabinoid receptors, and produce neurotransmitters such as dopamine and serotonin when we give them the food they want.

Microbes use this stick and carrot-cake approach to mold our cravings. They are very good at it, but their benefit is not always ours.

Cravings and Mood

Cravings may seem like a frivolous thing to worry about, but our food preferences are tightly linked to our mental state. Our microbiome can create many of the same neuroactive compounds that are behind antidepressants, anxiety drugs, and recreational drugs. These are the powerful levers our gut microbes can pull to modify our eating behavior.

That microbial muscle-flexing can lead to several outcomes, not all of them good. A well-fed and balanced microbiome presents a healthy bulwark against the nasty pathogens of the world. It can reduce anxiety and lift our mood. On the other hand, crappy diets that unbalance our microbiome can lead to obesity or anorexia, dangerous syndromes that are strongly comorbid with depression and anxiety. An unbalanced gut may make us avoid healthy foods and instead seek out the junk food adored by some of our more selfish bacteria.

We’ve been under the mistaken perception that we make our own food choices, but ignorance is no longer an excuse: We need to manage our microbes before they manage us and make us sick. It’s important, not just for our gut, but for our mood.

What to Do

Our gut microbiome turns over every half-hour or so because bacteria have a short life cycle. What you eat changes the composition of your microbiome; certain species thrive and others wither, depending on dinner. So, if you can override your bad cravings, you can effectively rebuild your microbiome in just a few days. Of course, that goes both ways—the lure of Oreos should not be underestimated, and you can be right back to where you started in a flash, a victory of microbe over prudence.

Still, all is not lost. You can build a better, healthier microbiome in no time at all. Here are some tips to deal with your junk-food crazed microbes:

• Increase the variety in your diet to increase the variety in your microbiome. Diversity prevents a bully microbe from dominating and pushing hard on your buttons.

• Eat more fiber. You can change your microbiome overnight with just a few good fiber-filled veggies like broccoli and artichokes — although to really make it stick you’ll need to eat these foods daily.

• Substitute: when you are craving that donut, choose strawberries instead. We tend to forget how good fruit is when confronted with a glazed delicacy. You may complain for the first few days (OK, maybe weeks), but once you’ve established a healthier microbiome, it just gets easier and easier.

• Exercise, not to lose weight, but to balance your microbes. Just walking for 15 minutes a day does your gut a world of good.

We tend to identify with our cravings; we think of ourselves as chocolate-lovers or meat-eaters. But knowing how much our microbes influence our cravings should make it easier to overcome them. After all, who do you want to oversee your diet: you or your selfish microbes?

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References

Temko, Jamie E., Sofia Bouhlal, Mehdi Farokhnia, Mary R. Lee, John F. Cryan, and Lorenzo Leggio. “The Microbiome, the Gut and the Brain in Eating and Alcohol Use Disorders: A ‘Ménage à Trois’?” Alcohol and Alcoholism 52, no. 4 (July 1, 2017): 403–13.

Hill, Alison L., David G. Rand, Martin A. Nowak, and Nicholas A. Christakis. “Infectious Disease Modeling of Social Contagion in Networks.” PLOS Computational Biology 6, no. 11 (November 4, 2010): e1000968.

Corrales-Carvajal, Verónica María, Aldo A Faisal, and Carlos Ribeiro. “Internal States Drive Nutrient Homeostasis by Modulating Exploration-Exploitation Trade-Off.” Edited by Iain D Couzin. ELife 5 (October 22, 2016): e19920.

Behary, Preeshila, and Alexander D. Miras. “Food Preferences and Underlying Mechanisms after Bariatric Surgery.” The Proceedings of the Nutrition Society 74, no. 4 (November 2015): 419–25.

Alcock, Joe, Carlo C Maley, and C Athena Aktipis. “Is Eating Behavior Manipulated by the Gastrointestinal Microbiome? Evolutionary Pressures and Potential Mechanisms.” Bioessays 36, no. 10 (October 2014): 940–49.