If you’re like a lot of people, you’re finding it harder and harder to stomach climate change—literally. A warming world leads to all manner of health problems, including increased risk of cardiovascular disease, exacerbation of pulmonary conditions like asthma and COPD, and mental health problems including depression and anxiety. Increasingly, however, climate change is being implicated in a range of illnesses of the gut, such as diarrheal diseases, irritable bowel syndrome, intestinal infection, and more. While the mechanism behind the increase in pulmonary disease in a warmer world is more or less direct—breathing hot, dirty, sooty air isn’t good for anyone’s lungs—the gut connection is more nuanced and multifactorial, involving crop growth, contaminated water supplies, droughts, heat waves, malnutrition, and the microbiome of the soil. None of this is good for us; all of it can affect any of us. Here’s what you need to know about the climate-gut connection.
How high temperatures directly affect the gut
The body is an exquisitely balanced system. We operate optimally at 98.6°F; nudge us up to just 99°F and we already start feeling unwell. It’s no wonder then that if the planet runs a fever we will pay a price. “Higher temperatures can increase stress hormones in the body, and that really affects gut physiology,” says Elena Litchman, professor of aquatic ecology at Michigan State University.
The principal stress hormone is cortisol, which is produced by the adrenal gland. Cortisol affects multiple parts of the body, but can have an especially powerful impact in the gut, which is lined with immune system cells; epithelial cells, which form a barrier between the intestines and the rest of the body; and enteroendocrine cells, which help regulate the hormonal environment of the gut. All of these cells have cortisol receptors, and all of them may become dysregulated if cortisol levels climb too high. Cortisol can also speed or slow the time it takes for food to transit through the intestines, which can lead to what’s known as dysbiosis—or an imbalance in the number, type, and distribution of the trillions of bacteria, viruses, and fungi that make up the microbiome inhabiting the digestive tract.
High temperatures are also known to increase the permeability of the intestinal lining, leading to so-called leaky gut. “Temperature has a direct effect on the intestines,” says Desmond Leddin, professor of medicine at Dalhousie University in Canada. “One of the causes of heat stroke is thought to relate to intestinal permeability.”
Leaky gut can also allow organisms that make up the intestinal microbiome—which are supposed to remain in the intestines—to migrate into the bloodstream and spread infection. The microbes that remain behind, meantime, can be thrown entirely out of balance.
“When the connections [in the intestinal lining] become less tight, you can have more oxygen getting into the gut,” says Litchman. “That may stimulate bacteria or other gut microbes that are not necessarily beneficial.”
The microbiome within you and without you
The makeup of organisms residing in the intestines is affected by climate change in other ways as well. It’s not just humans and other animals that have a microbiome; soil, air, and water do too, and higher ambient temperatures can cause less beneficial microbes—including listeria, e. Coli, and Shigella—to thrive there. What’s in the external environment quickly becomes part of your internal one too.
“Soil is a big source of microbes in the gut,” says Litchen. “The microbes are in food, they get on our skin, you can even inhale the soil microbiome in the form of dust.”
In the West and the rest of the developed world, that’s less of a problem because in those wealthier countries people are eating more processed food that is further removed from the soil that produced it. In developing, often agrarian countries it’s a different matter. “People in those parts of the world are in closer contact with environmental microbiomes,” says Litchen.
“There is definitely a shifting pattern in global digestive health,” says Leddin. “Of particular concern are the inflammatory bowel diseases—Crohn’s disease and ulcerative colitis. Crohn’s was relatively uncommon in lower income countries, but now it’s becoming more of a problem.”
Water presents worries of its own. High temperatures may increase the concentration of pathogens in the water at the same time we’re drinking more to cope with the heat, increasing the exposure to unhealthy bugs. “It’s basically kind of a positive feedback,” says Litchen. Meantime, if we don’t drink enough when it’s hot out, we can suffer from dehydration, which has gut implications of its own.
“When we’re dehydrated, blood gets shifted from muscles and the gut to the vital organs, especially the brain and the heart,” says Eamonn Quigley, chair of gastrointestinal health at Methodist Hospital in Houston. “This is not good for the gastrointestinal tract, which begins to suffer.” Digestive symptoms associated with dehydration include stomach pain and cramping, constipation, and slowed digestion and nutrient absorption.
Climate change can also lead to flooding, which has a direct knock-on effect in the gut. As Leddin wrote in a 2024 paper in Gastro Hep Advances, floods can contaminate ground water with Rotavirus, Cryptosporidium, Campylobacter, and Yersinia. That hits the developing world harder than the developed one. In 2004, for example, floods in Bangladesh resulted in 350,000 cases of diarrheal disease. But even in wealthy countries, there’s a real risk. In the U.S., 23 million households rely on private wells for their water supply—wells that can become easily contaminated during floods.
The role of diet
As much as anything, it’s what’s on your menu that most affects your gut health, and climate change plays a big role in what you’re eating—even if you don’t realize it. For starters, higher temperatures can lead to faster-growing crops. “That sounds good,” says Leddin, “but because they’re growing more rapidly they may have a lower nutritional value.”
What’s more, as Litchen reported in a 2025 paper in The Lancet Planetary Health, temperatures over 86°F can reduce the levels of beneficial antioxidants in foods, while raising the absorption of environmental arsenic by rice plants, both of which adversely affect the gut microbiome. Higher levels of carbon dioxide can reduce levels of zinc, iron, and protein in wheat, rice, and maize, which could lead to 100 million more people becoming protein-deficient and 200 million more zinc-deficient by 2050. Higher ocean temperatures may also reduce the availability of fish and seafood, lowering protein intake and changing microbiota composition, especially in low- and middle-income countries.
“There is a phenomenon called ‘hidden hunger,’” Litchen says. “Basically it means that you’re consuming the same amount of food but the nutritional quality of the food changes. There are fewer nutrients and the food is harder to digest.”
Direct hunger—simply not getting enough to eat, whether the food is of high quality or not—is also becoming an increasing concern as an overheated climate and extreme weather cause crops to fail, often in already disadvantaged parts of the world. “As more areas of the world become inhospitable to agriculture, the problem is only going to become greater,” says Quigley. “There’s a very nice correlation between the diversity of your diet and the diversity of your microbiome, and in terms of the gut, diversity is a good thing.”
If climate change gets solved at all, no one pretends it’s going to be solved anytime soon. Last year was the warmest one on record, displacing 2023, which had briefly held that distinction, and the past decade represents the hottest 10 years ever. The planet is suffering at our hands—and increasingly, our own health is too.