Minute 4: How to fuel without upsetting your stomach in the heat

Running in hot weather doesn’t just put extra strain on your muscles - it turns out you need a gut check too. According to “Why Heat Causes GI Stress & How to Adapt Your Fueling Strategy,” intense exercise in hot conditions redirects blood away from the digestive organs toward working muscles and the skin, reducing gut perfusion and making nausea, cramping, and poor nutrient absorption more likely.

Heat also changes how your body uses fuel. One 2025 study cited in the article found that runners maintained optimal hydration yet still oxidized about 20% less of the carbohydrates they consumed during exercise than they did in temperate conditions. That means piling on extra gels can backfire when your gut is already under strain.

A better approach may be smaller feedings of 15 to 25 grams every 15 to 20 minutes, preferably from glucose-fructose blends that use separate intestinal transporters. Fluid intake should also reflect your own sweat rate, workout intensity, and conditions, while avoiding dehydration beyond roughly 2% to 3% of body weight. Afterward, the article recommends replacing 100% to 150% of fluid losses.

Cold drinks may offer a modest cooling benefit too, which brings us back to our post from last week: “Grab a big gulp on your next hot-weather run.” A slushie can combine fluid, carbohydrates, and ice during a long, hot session, provided its sugar and electrolyte content fits the workout. Just be sure to practice your plan before a hot race day, because that’s a poor time to experiment with fresh fueling strategies.