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Your Top 5 Summertime Qs, Answered

Summer means sunshine, traveling, colorful in-season produce, and more. Here we unpack five frequently asked questions pertaining to the shift in season, and how it influences your body and your microbiome.

6 minutes

15 Citations

For our friends in the Northern Hemisphere, summer is in full swing. As you make your summer plans, remember that there’s an invisible world of microbes experiencing the season with you, including the 38 trillion bacteria and other microbes that comprise your microbiome and call you home.1 Whether you’re traveling, rock-collecting, soaking in the sun, or backyard BBQing, they’re along for the ride.

Here, our SciCare team* unpacks five frequently asked questions from our community (you!) about the invisible interactions of the season, and how they influence your body and your microbes. 

* 👋 SciCare is our team of experts who answer all your science, health, and product-related questions. Have a question of your own? Email

Why is my digestion always disrupted when I travel?

When you leave home, your trillions of resident microbes are traveling with you. And just like you, they’re affected by shifts to your sleep schedule, changes in diet, exposure to new microbes (including pathogens), and excess stress, all of which can disrupt your gastrointestinal system and digestion. 

Because the process of digestion is a highly complex string of events orchestrated by various hormones, chemical messengers, enzymes, and muscular movements, there’s a lot of opportunity for disruption, especially with the changes to environment and routine that accompany traveling. Take gut motility (the movement of food from the mouth through the body), for example. Your body operates on a 24-hour cycle, known as your circadian rhythm or “molecular clock,” which contributes to the regulation of gut motility.2 When your circadian rhythm is disrupted (which can happen with shifts to meal times and sleep schedules), it can impact how food and waste move through your system. 

Emerging data even shows that your gut microbiome has its own circadian clock—exhibiting daily oscillations in its composition.3 The abundance of certain groups of bacteria peaks during one part of the day (morning) then crash in another (night). Changes to your normal “rhythms” induce what is known as “circadian misalignment,” which can lead to impairments in physiological functions like digestion. This is why gastrointestinal discomfort, constipation, diarrhea, or stomach upset are common experiences when we travel.

So, how can I support a healthy gut while traveling?

In order to minimize travel-related disruption to your digestive system, stick to your routines where possible. Here are four key areas to focus on:

  1. Prioritize your sleep schedule. Your circadian rhythm plays a key role in maintaining homeostasis of the microbiome, and jet lag can cause an imbalance of your gut microbiota.4 In a 2014 study, jet-lagged participants showed an increase in bacteria known to be more prevalent in the gut microbiome associated with obesity and diabetes. However, levels of bacteria returned to their pre-travel state once the travelers recovered from jet lag, about two weeks after landing.5 
  2. Hydrate. Hydration keeps food moving through your system. It’s also critical to the health of your stool as poop is around 75% water. Inadequate fluid intake can cause stools to become dehydrated and difficult to pass, and can be a leading contributor to constipation.6
  3. Move around. Sitting still on a plane or in a car for long periods of time can slow your transit time. Movement increases blood flow to your intestines, which can stimulate muscle contractions that help waste pass through. Additionally, exercise may reduce symptoms of constipation and can help decrease inflammation within the gut, which may be beneficial in preventing certain digestive issues.7
  4. Take a probiotic formulated with clinically validated strains, and prioritize consistent intake. Probiotics are generally transient microbes, meaning they travel through your gut to deliver benefits, interacting with local cells and resident microbes, before exiting your system. For example, certain strains trigger neurotransmitters that stimulate muscle contractions for increased motility.8 Given their transient nature, probiotic efficacy is dependent on continuous consumption. This means maintaining your routine, even while you’re on-the-go, is important to ensure probiotics deliver consistent benefits. 

Speaking of travel, do probiotics survive shipping in the heat?

This is a question we receive often, especially considering the common misconception that all probiotics need to be refrigerated. If that’s the case, they can’t possibly survive shipping in the summer heat, right? Well, contrary to perishable food products, refrigeration doesn’t mean “freshness” or superiority for bacteria. In fact, if a probiotic does not survive at room temperature outside of the refrigerator, it can reflect weak stability of the product, lack of appropriate probiotic protection (through capsule technology and packaging), or inadequate overages in formulation (overages help ensure label claims are met throughout the duration of shelf-life). 

The more important thing to pay attention to is quality assurance testing, which validates shelf-stability and survivability through shipment, shelf-life, and digestion, regardless of the storage conditions.

We’ve conducted extensive testing on our synbiotics, including heat sensitivity, to ensure live bacteria arrive at your door safely. After 10 days of constant, 24-hour, 100º F exposure, our probiotic bacteria counts and viability exceeded the living cell counts (AFU) stated on our label. Translation: Our DS-01® and PDS-08® beat the heat.

Will eating seasonally impact my microbiome?

While the gut microbiome remains relatively stable over time, there is seasonal variation in your microbial makeup. These shifts may be explained, at least in part, by dietary fluctuations that occur across the seasons. Think: eating more fresh produce in the summer and more canned or frozen produce in the winter. The problem is, modern living has disrupted these natural fluctuations. We now have access to most produce year-round, and we collectively eat more packaged and processed foods than we used to. This means our gut bacteria may not be as dynamic as they were for our hunter-gatherer ancestors.

A 2014 study found that the gut microbiome of Hadza tribe members in Tanzania exhibits seasonal fluctuations in composition and function, reflecting the availability of certain foods at different times of the year.9  For example, in the “dry season” (October to May), when the Hazda consumed more meat, their gut microbiomes showed enrichment in enzymes associated with animal carbohydrates. This means the microbial community present during the “dry season” might be better equipped to break down and use animal carbohydrates during this time, when animal consumption is at its highest in the year. When researchers compared these findings to the microbial profiles of industrialized populations, they discovered that the most seasonally dynamic bacteria in the Hadza microbiota were rare or absent, regardless of season, in “modernized” humans.

While “modernized” humans are lacking certain types of these cyclical bacteria, there are still benefits that may occur when eating seasonally. Incorporating more locally grown seasonal foods into your diet can encourage intake of a range of fruits and vegetables (which is a strong predictor of gut microbial diversity10), decrease intake of processed foods loaded with additives (such as artificial sweeteners and emulsifiers), and reduce pesticide exposure (which can negatively impact the gut and soil microbiome11,12).

Some of our favorite microbiome-nurturing summer foods include bell peppers, berries, corn, mango, peaches, tomatoes, cantaloupe, squash, grapes, and zucchini.

Does vitamin D impact the gut microbiome?

Yes! When your skin is exposed to the sun, UVB rays stimulate the production of vitamin D, which is most often talked about in the context of calcium absorption and bone health, but actually has a range of functions within the gut. For example, vitamin D influences bacterial colonization (what microbes are taking up residence in your gut) by triggering the production of antimicrobial peptides (AMPs). AMPs are molecules that inhibit the growth of pathogenic bacteria and, as a result, help shape the microbiome to have a “healthier” composition.13

Vitamin D is also involved in maintaining the integrity of the gut barrier and repairing tissue damage that occurs along the gut wall by increasing the expression of tight junction proteins.14 Tight junctions form scaffolding to reinforce the gut barrier and keep out foreign materials and contaminants.

While spending time in the sun is good for your gut, there is a complex balance to consider: You need sunlight for vitamin D production, but overexposure can lead to sunburns, sun damage, and even skin cancer. So, what should you do?

In general, short bursts (5-15 minutes) of midday sunlight exposure a few times per week is enough to maintain healthy vitamin D levels,15 though this can vary depending on factors like how close you are to the equator, how much skin is exposed, time of year, sunscreen usage, and skin color. (Reminder: Please wear sunscreen, reapply, and don’t spend too much time in direct sunlight.) In addition to sun exposure, you can obtain vitamin D from foods like salmon, egg yolks, and mushrooms, as well as through supplementation.

We receive and answer questions like these every day. Stay tuned for more SciCare roundups on Cultured. If you have any questions of your own, email us at


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