When the human body is taxed by things like hot weather and exercise, it prioritizes its functions. Cooling itself and protecting vital organs takes precedence, while functions such as digesting complex foods become secondary. Likewise, the decisions you make on what to put into your body will dictate how well your body can perform and hold up under these stressful conditions.
Water becomes especially important when the heat index is high. It makes up most of your blood, which distributes oxygen and nutrients throughout your body [source: Ryan]. But as counterintuitive as it might sound, it's possible -- and fairly common -- for inexperienced athletes to drink so much water that they experience hyponatremia, or water intoxication. Drinking in excess of 1,500 milliliters (50.7 fluid ounces) of water in a 60-minute period can lead to the dangerous condition [source: Better Health]. Water flushes vital electrolytes from the body, so hydration using a sports drink that contains sodium and carbohydrates is important [source: Zelman].
Foods high in water content like fruits and vegetables can be valuable before, during and after exercise. Focus on foods that are easily digestible, low in fat and contain carbohydrates and protein. Examples include pasta, bread and fruits. This is not the time for fast food [source: Zelman]. Unfamiliar foods should be experimented with at another time as your stomach may be particularly sensitive. Energy gels are popular because they are easily digested and contain fast-acting carbs and sugars. Many of these gels are designed with the ideal ratio of protein and carbohydrates in mind for an athlete in the midst of high exertion.
Weekend warriors or professional athletes can and do perform effectively in hot weather, but it's also common for them to falter and even hurt or kill themselves when they don't give enough respect to the dangers of heat. Proper nutrition and a health dose of awareness can go a long way.