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What to Give Your Microbes for the Holidays

You take your microbes to every party, but what do they want?

"The secret of success in life is to eat what you like and let the food fight it out inside." ―Mark Twain.

Your gut microbes are excited: The holidays are chock full of socializing, rich food, tasty treats and plenty of booze. There are a hundred trillion microbes in your gut, and like film noir, it's sometimes hard to tell the good guys from the bad. For instance, everyone harbors sturdy colonies of E. coli, Streptococcus and C. diff—well-known pathogens—but they are quite reserved, even helpful, most of the time.

The trick is to maintain diversity, the principal attribute of a healthy gut. No matter what certain TV curmudgeons might tell you, diversity is good. It provides a rich ecosystem, creating a stable balance and keeping bully bacteria at bay.

I know what you're thinking: What could be more diverse than holiday treats like sugar cookies, peanut brittle, almond bark, polvorones, chocolate chip cookies, ginger snaps, butterscotch, coconut macaroons, snickerdoodles, fruitcake, pfeffernusse cookies, fudge, candy canes, eggnog, gingerbread men, butter cookies, rugelach, brownies, caramels, peppermint bark, blondies, whoopie pies, chocolate truffles, pignoli cookies, red velvet cake, buckeyes, toffee balls, pecan crescents, Mexican wedding cookies, rum balls, pinwheels, and Russian tea cakes?

Caught you! It's hard to resist holiday sweets.
Source: iStock

Yes, this is diverse but also perverse. These delicious "foods" are as treacly as a cheap valentine card.

Sugar is naughty

Sugar unbalances your microbiota, encouraging certain bacteria at the expense of others. Sugar is easy for your body to absorb and most of it gets digested quickly, starting in your mouth and continuing throughout the gut. That means sugar-loving bacteria—the lollipop gang—have to live close to the source before it all gets soaked up. Normally, they are not numerous, but with each cookie, they expand their turf.

When you feed those particular microbes the sugar they crave, you encourage them to multiply. That fertile colony can double in size every half hour.

Unfortunately, the small intestines aren't well designed to deal with bacteria. Unlike your colon, fortified to house some three pounds of microbes, your small intestines are more delicate and vulnerable. Boosting the growth of these sugar-loving microbes can lead to problems like IBS and Crohn's.

But microbes don't want you to think about those problems. In response to sugar, they produce dopamine, a neurotransmitter. Yes, shockingly, bacteria can produce the same exalted chemicals that nerve cells use to communicate. Dopamine activates reward centers in your brain, causing you to feel like you just hit the jackpot. Any cookie that rings that bell deserves a second helping, or third. That causes a bigger bloom of the lollipop gang, and more dopamine.

And thus, the joy of holidays.

Eggnog is weird

To wet your whistle, you slurp down some eggnog with a dollop of brandy. This is an unholy beverage designed to get you buzzed enough to forget that you are drinking a major calorie bomb made with raw eggs. That creamy quaff causes your gallbladder to squirt out bile, an emulsifier that starts the breakdown of fats.

Bile is also an indiscriminate antibiotic, killing microbes as it trickles through your gut—except for bilophila, bacteria that are just fine with a little bile. Their name, Latin for "bile lover," gives the game away. These bacteria are not always team players. They can get out of hand and cause inflammation. That's probably a good reason to only drink eggnog once a year.

That holiday buzz

Not to be a Debbie downer, but the brandy in your nog can be problematic. Alcohol can make your gut more permeable, even leaky, allowing toxins and pathogens to gain access to your bloodstream. From there, your heart cheerfully pumps that toxic load to every organ in your body. That's a great way to develop systemic inflammation.

Alcohol adds fun to your evening but extracts it from the next morning. You don't have to abstain—you may have to deal with relatives, after all—but if you find yourself wearing a lampshade, you might want to dial it down.

The social scene

The year-end celebrations bring people together from all over the world, many of them bearing exotic diseases. These parties encourage hugging and kissing, surefire methods of transmission. Adults may be hard to avoid, but never touch snotty-nosed children—they are fevered cauldrons of pestilence.

Some scientists speculate that people get together at the instigation of their microbes, which are looking to spread themselves to new territory. By this theory, we are mere fleshy fermentation vessels, driven to pass on our microbial gifts via party behavior. Fortunately, thanks to jet travel, diseases have already spread themselves around the globe, so you're unlikely to be exposed to anything dramatically new.

But really, avoid children. There's a reason they have their own table.

Fiber is nice

So the party trio of fat, sugar, and alcohol is a major treat for some of your microbes, but unfortunately, mainly the ruffians. Most of it never gets past the small intestines.

Meanwhile, the good microbes are idling in your colon, like trillions of Tiny Tims, patiently hoping for a handout. All these pitiful microbes want is a little fiber. We don't get enough of that in general, but it gets exceptionally short shrift in the holiday season. We want candies and schnapps, not broccoli and flaxseed.

That's a shame because your good bacteria can nourish and heal your gut lining, repairing party damage and preventing disease. In fact, your good bacteria are the first line of defense against pathogens. Don't take them for granted: They are life savers so treat them right. Your mom probably mentioned this, but eat some vegetables.

The party mood

What is this alcohol- and sugar-fueled inflammation doing to your mind? Well, we now know that there is a connection between the gut and the brain: If you abuse your gut for long enough, depression and anxiety can set in. Sugar can spike anxiety, and chemically speaking, alcohol is a depressant.

The holidays are potent triggers for mood swings. Just Google "holiday depression" to see how popular it is. Interestingly, our diet has a lot to do with that. Food poisoning, for instance, can lead to IBS and depression. On the plus side, some microbes can cheer you up. These are called psychobiotics. As you might have predicted, psychobiotic microbes enjoy veggies, not alcohol and sweets.

Some holiday survival tips

You can make delicious treats without so much processed flour and sugar. Here are some tips:

  • Almond flour has more fiber than cake flour and can substitute in many recipes.
  • Some prebiotics, like FOS, GOS, yacón syrup, inulin, and others, are sweet and can substitute for sugar.
  • You can make delicious desserts that aren't so sweet: chop walnuts, dates, coconut, and cocoa beans in a food processor. Make balls from the dough and freeze them.
  • Try savory treats, like cheddar, cranberry and pistachio cookies. They have a lot less sugar.
  • Substitute dates and dried fruit for sugar. It's still sugar, but it comes with a palliative dose of fiber and polyphenols, which are treats for your good microbes.

Work it off

For kids, the holidays are a mad sugar rush. As they chase each other and knock over your favorite lamps, they are working off their cookies.

Now look at the traumatized adults, trying to stop the carnage but mostly cowering on the sofa, often watching athletes run around on TV. Sadly, channel surfing is not actually exercise. If you insist on gorging, then try to get off your butt. You're not a kid anymore.

In sum

This may sound like Scrooge-like advice, but it really isn't humbug. If you do it right, you can be even happier this New Year.

Dialing down the sugar, fat, and alcohol is the key. And that—along with a little fiber—is the best present to give your microbes this holiday season. Cheers!


Stilling, Roman M., Seth R. Bordenstein, Timothy G. Dinan, and John F. Cryan. “Friends with Social Benefits: Host-Microbe Interactions as a Driver of Brain Evolution and Development?” Frontiers in Cellular and Infection Microbiology 4 (October 29, 2014).

Dinan, Timothy G., Catherine Stanton, and John F. Cryan. “Psychobiotics: A Novel Class of Psychotropic.” Biological Psychiatry 74, no. 10 (November 15, 2013): 720–26.