A runner on the 3,080-mile Race Across the USA (RAUSA) in 2015. Some of the RAUSA runners were included in a study to determine the metabolic limit for how much energy the body can absorb from food for endurance events. (Credit: Bryce Carlson)

Many marathon runners know the boost that can come from popping a mid-race energy gel. (Mmmm, calorie-rich goop.) But according to new research published in Science Advances, when it comes to endurance events, there’s a limit to how much energy the hum