Seth Rakoff-Nahoum, MD, PhD, a Boston Children’s Hospital physician-scientist who does infectious disease research and is taking an evolutionary approach to understanding the human microbiome and its effect on health, offers us some insight into what’s happening to the bugs in our gut as a result of the Thanksgiving meal.
Q: Does the traditional American Thanksgiving meal affect the human microbiome?
A: Anything you put in your body has the potential to affect your microbiome, and Thanksgiving dinner is no different.
Thinking about the typical type of foods we eat — turkey, stuffing, cranberry sauce, sweet potatoes, mashed potatoes, green bean casserole, parsnips, gravy — that’s a very diverse meal in terms of simple sugars, complex sugars, proteins, saturated and unsaturated fats.
The “bugs” in our gut get energy from what we’re eating, and certain microbes are better at consuming certain food molecules than others. In fact, some bugs convert tryptophan, found in turkey, into agents called “indoles” that can impact immune system regulation.
The body actually sees indole as a toxin, so you’ll produce enzymes to neutralize it. There’s a lot more we need to learn about indoles – but for now, there’s no indication at all that it’s a reason to skip the turkey.
There is a lot of evidence that no matter what sort of major perturbation you have in your microbiome, the population of bugs in your gut will bounce back to its equilibrium in a pretty short period of time. Except for when you take antibiotics, which can really wipe out a lot of the resident bugs and then it takes longer for them to re-populate the digestive tract.
Q: How does the microbiome’s host choose its Thanksgiving “guests”?
A: Much like the way the front door opens and without looking you know it’s your least favorite aunt based on the signature cloud of perfume swirling around her, your body may also have recognition and memory mechanisms that sense who’s present in your gut. I think this chemical sensing and learning is a very interesting avenue for the future of medicine.
Similarly, at any given time, there are pathogens in your gut that we know can be problematic under some circumstances, but most of the time they aren’t causing any problems.
To avoid unwanted guests, our body sometimes relies on olfactory cues for identifying foods that could cause infection. In food that’s rancid and crawling with potentially dangerous microbes, a molecule called putrescine forms which given off a putrid scent. You’re not going to eat something that smells disgusting! That’s your body’s way of identifying a threat to your health and creating an aversion response to prevent that food from getting into your digestive tract.
That being said, we don’t yet know how many troublemakers can be identified ahead of time based on visual and olfactory cues that your body recognizes as threatening.
Some threats aren’t as obvious – Shigella, for example, is a type of bacteria closely related to E. coli that can be found on unwashed, raw vegetables. There’s no way to detect it by sight or smell. If you swallow so many as ten Shigella organisms, you’ve hit the dose threshold for getting sick. While your microbiome does have some ability to protect you from getting infected with some strains of bacteria, there doesn’t seem to be a protective mechanism in place to combat Shigella before it has the chance to infect you. So, always wash your veggies, people!
Ultimately, the response to food poisoning can be a mechanism your body uses to kick out unwanted guests who are causing trouble.