Does Heat Impact My Gut Health?

Fall may be approaching, but in many parts of the world, we’re still experiencing record-breaking temperatures and heat waves. These warmer temperatures mean a change in environment and a shift in many aspects of your day to day: the foods you eat, the products you use, what you wear, and how and where you spend your time. So what does this mean for you and your microbes? 

Here, our SciCare team* explores four questions from our community (i.e., you) about heat, the microbiome, and your health. 

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

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Does heat impact my gut health? 

For ethical reasons, there is little direct experimental evidence on the impact of heat on the human gut. Animal studies, however, have shown that heat stress can alter the composition and diversity of gut microbes,¹ including a decline in a beneficial group of bacteria (Firmicutes) that are important for producing short-chain fatty acids (SCFAs).² SCFAs are compounds that confer a range of powerful benefits in the body. For example, they support your gut barrier, which manages immune responses and helps keep pathogens out. They also support gut-brain communication, which influences not only digestion, but mood, cognition, and mental health.³ While it’s generally not considered good to “lose” bacteria that produce SCFAs, the microbiome is resilient and can bounce back from temporary disruptions. So we wouldn’t expect one extra hot day to have a long-term impact on your gut health—especially if you’re eating a fiber-rich diet, which certain gut microbes can use to produce SCFAs.⁴

Should I drink warm, room temperature, or cold water? Does it matter? 

There isn’t much scientific research on the impacts of drinking warm versus cold water on the gut specifically, though warm water may help with digestion because it dilates blood vessels, which can enhance circulation and support toxin removal. On the other hand, cold water might hinder digestion by constricting blood vessels—though one 2013 study suggests cooler water (~60°F) may be the better option if you’re looking to rehydrate after exercise or exposure to warm environments because the cold liquid helps regulate body temperature faster.⁵

Regardless of temperature, hydration is critical for your gastrointestinal health, and it’s especially important during warmer months when you’re likely to lose more water to sweat. In the gut, hydration is important for digestion, intestinal permeability (what can pass through your GI tract into your bloodstream), nutrient absorption, motility (how food and waste move through your digestive system), and bowel movements (fun fact: healthy stool is ~75% water⁶). Dehydration can lead to slower transit time, which may result in the overgrowth of harmful bacteria and a decreased diversity of beneficial microbes.⁷

While you’ve probably heard the old adage “drink eight glasses of water a day,” it’s important to remember that hydration does not solely rely on plain drinking water—20-30% of your hydration needs can come from diet.⁸ Case in point: A cucumber is ~96% water. Some microbiome-nurturing foods that are especially high in water content include watermelon, tomatoes, lettuce, mushrooms, apples, peaches, and zucchini. 

Can I take DS-01® with hot beverages? 

If you’re someone who prefers their cup of joe hot, we have good news: It’s perfectly fine to drink hot coffee (or other warm beverages) alongside your DS-01^®.

This is the case for two reasons. First, hot beverages are diluted in your stomach when encountering stomach acid, which naturally buffers the heat. Second, our ViaCap^® capsule is designed to protect probiotic organisms. The prebiotic outer capsule acts as an elegant barrier to oxygen, moisture, and heat to safeguard and ensure the viability of the probiotic inner capsule. In fact, we tested this in a premier model of human digestion (SHIME^®), and demonstrated that the ViaCap^® is able to withstand the harsh conditions of the stomach and protect the probiotic organisms on its way to the target site (the colon). 

What about the acidity of coffee? Fortunately, this is also not a problem. Through SHIME^® testing, we’ve demonstrated that our ViaCap^® capsules survived through the pH of stomach acid (1.5–3.5). This means coffee (with a pH of ~5) is likely not acidic enough to damage the bacteria.

I’ve read about bacteria in the ocean. Should I be concerned? 

If you’re cooling off with a dip in the ocean, you should know: Oceans are filled with bacteria. In fact, it’s estimated that there are 100,000,000x more bacterial cells in our planet’s oceans than stars in the observable universe—that’s 1.3 x 10²⁹ bacterial cells!⁹ While the majority of these bacteria are not harmful, recreational beach waters can become contaminated by wastewater and storm runoff, which may be a source of pathogens (like Salmonella spp. and Staphylococcus aureu) that can make you sick when you come in contact with the water. There are also native ocean bacteria that can cause illness (mostly skin infections), like certain members of the Vibrio species.

Your skin microbiome is the first line of defense against any harmful bacteria you may encounter while you’re jumping waves. Among its critical functions, it reinforces your skin barrier and can even directly kill or alter the virulence of pathogens by secreting antimicrobial molecules.¹⁰ But your skin microbiome is not immune to change, and coming in contact with ocean water can impact your own native bacteria. 

In a 2019 study, researchers collected skin microbiome samples from participants in Huntington Beach, CA.¹¹ Each individual’s skin microbiome was different from their fellow swimmers’ before they entered the water (as expected). However, post-swim, the microbial communities were no longer different, and analysis showed that ocean bacteria (including potential pathogens) had replaced native skin bacteria, remaining there for at least 24 hours post-swim. Building on this, another study conducted two years later also observed shifts in native skin microbes post-swim, as well as an increase in the abundance of certain genes, including antibiotic resistance genes (ARGs), that could promote the ability of bacteria to cause infections and make them more resistant to antibiotics.¹² However, it’s possible that the skin microbiome could return to its native composition in the days or weeks following—both studies did not assess long-term (that is, post-24 hour) changes to the skin microbiome.

This may sound scary, but before you swear off the ocean, these changes to your skin microbiome don’t mean there’s a definite increased risk of picking up harmful bacteria. Millions of people swim in the ocean each year, and very few actually contract an infection. If you are swimming, just be mindful of what’s happening at a microbial level and pay attention to beach water quality advisories that will let you know if ocean water contains elevated bacteria levels. You can also take small steps including rinsing your skin with fresh water immediately after swimming and avoiding the ocean if you have open wounds to mitigate any risk of infection. 

More microbiome questions? Email us at scicare@seed.com and stay tuned for more SciCare roundups on Cultured.