Your Gut Would Like a Word
I have a cold. I'm going into week two. And when I say I am battling, I am not exaggerating. I'm taking vitamin C like it's candy. I'm getting rest and eating OK. I'm doing what I can to keep it from going from my nose and sinuses into my chest, but I feel like I'm not going to be the victor here.
I won't pretend I have some glamorous wellness routine when I get sick. I don't. What I do have is an obsession with gut health. So having a cold comes with one predictable mental side effect for me: eventually, I start wondering whether my gut has anything to do with what's happening in my nose. And guess what? Turns out the answer is "probably."
You've likely heard the old advice to feed a cold and starve a fever. I'll leave the fever half to your doctor. The feeding half turns out to be more interesting than folk wisdom has any right to be, though not the way anyone intended. If the research is any guide, the feeding that counts happens weeks before the cold shows up, and the ones you're feeding are your gut microbes.
Why Original Age is talking about your nose.
Your gut isn't just a big, long tract that processes lunch. It's one of the body's busiest places for communication between the outside world, the microbes that live in and on us, and the immune system.
Your intestinal lining acts as a barrier. Immune cells sit close by. Gut microbes and the compounds they produce can interact with that local immune environment, which in turn can influence immune activity beyond the digestive tract. That doesn't mean a healthy gut makes you invincible, or that every sniffle is a microbiome problem. It means your gut and immune system are genuinely connected, and not in a vague "everything is connected" way.
About 70% of your immune system is in your gut.
You may have heard that before. What it means is that the gastrointestinal tract contains a large amount of immune tissue and is a major site where the body learns what to tolerate, what to respond to, and how to maintain a healthy barrier. So yes, a gut company like mine, Original Age, can reasonably care about cold season. The leap we should avoid is assuming that a gut-focused product is automatically a cold remedy.
What the research actually says.
Studies have looked at whether probiotics may help prevent upper respiratory tract infection, the category that includes many common colds, and whether they affect how often people get sick, how long symptoms last, and how severe they feel.
A 2022 Cochrane review pooled 24 randomized trials involving 6,950 people, from young children to older adults. Compared with placebo or no probiotic, probiotics may have reduced the number of people who developed at least one upper respiratory tract infection. The review also found that probiotic use may have reduced the average duration of an illness episode by about 1.2 days. But the authors rated both findings as low certainty and called for larger, better-designed studies. The review's most solid finding, rated moderate certainty, was that people taking probiotics were less likely to be prescribed antibiotics for these infections.
Another systematic review and meta-analysis, focused on nonelderly adults, found a similarly modest pattern: orally consumed probiotics were associated with reductions in the risk, duration, and severity of respiratory tract infections. The authors' word for the effect was "modestly."
Let's be real. "May reduce" is not the same as "will prevent." And "about a day shorter" is not the same as "you will wake up cured tomorrow." But I'm liking these findings. So let's dig deeper.
A 2025 network meta-analysis compared oral supplements for preventing respiratory infections in adults. Multi-strain probiotics landed in the top three for reducing how often people got sick (roughly 10% fewer infections than placebo), alongside catechins, compounds found in green tea, and one specific Bifidobacterium strain. They were also linked to symptoms that ended about a day sooner and felt somewhat less severe.
That's relevant because (ahem) my company's product, Original Biome, uses a multi-strain approach. Now, it's important to say plainly that these studies weren't studies of Original Biome. Research on one strain, dose, product format, or combination can't automatically be transferred to another supplement simply because both are called probiotics.
That's not disappointing. It's just how the science works, even if hope runs rampant in the gut-health world.
Reality check.
This is the part where I would love to say, "Great news. Take a probiotic on day four of a cold and carry on." I can't say that. For three reasons.
First, these were mostly prevention studies. Participants generally took probiotics consistently for weeks or months, often throughout cold season. Starting a probiotic during an active cold isn't the same intervention researchers studied.
Second, the effects were modest. A cold that's about one day shorter may be meaningful, especially during a busy week. It's not a cure.
Third, strain matters. "Probiotic" is a broad category, not one single intervention. Studies use different strains, combinations, doses, delivery formats, populations, and definitions of illness. Results vary, which is one reason researchers remain careful about how confidently they state the benefits.
The research gives us a reason to be interested. It doesn't give us permission to overpromise.
Where fermentation comes in.
If you've followed my articles, you know fermentation is rarely left out of the conversation. Here, it's a gut-health detour worth taking.
A Stanford-led randomized study compared a high-fiber diet with a diet high in fermented foods. In the fermented-food group, researchers saw an increase in microbiome diversity, with bigger effects from larger servings, and lower levels of 19 inflammatory proteins in the blood.
Pretty interesting. But still not evidence that kimchi, yogurt, kefir, sauerkraut, or kombucha prevents colds. As much as I loathe constantly reining in my enthusiasm, my credibility would be at risk if I didn't point out the limitations. The study was small, involving 36 healthy adults. Eighteen people followed the fermented-food diet. It measured changes in the microbiome and immune-related inflammatory markers, not cold frequency, cold duration, or cold severity.
Still, it supports a bigger point. A gut-supportive routine may be one useful way to care for your overall health during cold and flu season.
What to do this season.
So yes, feed a cold. Just start before you have one, and think less about a miracle product than about the boring but helpful basics.
- Eat fermented foods you enjoy, such as yogurt, kefir, kimchi, sauerkraut, miso, or another option that fits your routine.
- Aim for more plant variety throughout the week. Your grocery cart doesn't need to be perfect. It just needs to contain more than the same three things on repeat.
- Protect your sleep. It's not exciting advice. Take it anyway.
- Don't ask for antibiotics for a typical cold. Antibiotics don't work against the viruses that cause colds.
- If you choose to use a probiotic, think in terms of consistency over months, not a last-minute fix on day four of a cold.
If your symptoms are severe, worsening, or concerning, contact a healthcare professional.
And here's the regularly appearing, shameless plug. Original Biome is a multi-strain probiotic for people who want a simple, consistent part of a gut-health routine.
It isn't marketed as a treatment for colds or flu. The studies discussed here involved specific strains and formulations, not Original Biome itself. But if you're already building habits around plant variety, fermented foods, sleep, and everyday gut support, Original Biome can be one practical part of that broader routine.
Ah-choo!
Disclaimer: This content is for educational purposes only and is not medical advice. Statements about Original Biome have not been evaluated by the U.S. Food and Drug Administration. Original Biome is not intended to diagnose, treat, cure, or prevent any disease.
References
- Vighi G, Marcucci F, Sensi L, Di Cara G, Frati F. Allergy and the gastrointestinal system. Clinical and Experimental Immunology. 2008;153(Suppl 1):3-6. https://doi.org/10.1111/j.1365-2249.2008.03713.x
- Zhao Y, Dong BR, Hao Q. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database of Systematic Reviews. 2022;(8):CD006895. https://doi.org/10.1002/14651858.CD006895.pub4
- Coleman JL, Hatch-McChesney A, Small SD, et al. Orally ingested probiotics, prebiotics, and synbiotics as countermeasures for respiratory tract infections in nonelderly adults: a systematic review and meta-analysis. Advances in Nutrition. 2022;13(6):2277-2295. https://doi.org/10.1093/advances/nmac086
- Zhu Z, Zhu X, Chu Y, Zhang B, Chen Y. Comparative effectiveness of oral nutritional supplements in preventing respiratory tract infections among adults: a systematic review and network meta-analysis. eClinicalMedicine. 2025;88:103479. https://doi.org/10.1016/j.eclinm.2025.103479
- Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153. https://doi.org/10.1016/j.cell.2021.06.019
- Centers for Disease Control and Prevention. Preventing and managing common cold. https://www.cdc.gov/common-cold/media/pdfs/2024/04/CommonCold_fact_sheet_508.pdf
