Optimizing Workout Nutrition for Hot Weather

It’s Saturday morning and it’s going to be 85 degrees by 9:00AM, or maybe you have a workout or race scheduled for the afternoon when it will be really hot. It’s nice to say things like “exercise when it’s cooler”, but sometimes busy athletes have to get out there when they can, even if that means when it’s hot. Plus, if you’re planning on competing in the heat, it’s important to spend enough time in hot environments to adapt and understand how your body responds to high temperatures. So, since you’re not going to shrink away from riding in hot weather, here’s how to optimize your workout nutrition for optimal performance.

Hydration Drives Nutrition

Your ability to deliver calories to workout muscles is highly dependent on your hydration status. During exercise, especially in hot weather, there’s a serious fight for resources going on over your blood volume. Your muscles want oxygenated blood to keep going. Your skin wants blood in order to get rid of excess body heat and your sweat glands pull fluid from blood plasma to create sweat. And your gut wants blood flow to keep moving nutrients into the body. When push comes to shove, temperature regulation trumps muscular work and both trump digesting food. In other words, in hot weather digesting food isn’t your body’s top priority; if you’re dehydrated and overheated your gut slows or stops and you don’t get the nutrients you need. During longer events in the heat, this reduced gut motility often leads to nausea and GI distress, which are leading causes for DNFs in ultraendurance events.

Separate Hydration From Calories

In recent years there has been a lot of debate between researchers, coaches, and athletes about the use of sports drinks vs plain water. I think both belong in a well-designed hydration strategy. Sports drinks can be a convenient way to deliver carbohydrate and electrolytes, and the taste and electrolyte concentrations have also been shown to drive athletes to consume more fluid every time they grab a bottle and more total fluid per hour. Those are good things.

At the same time, especially in heat, athletes need the ability to adjust fluid and calorie intakes independently. Separating your calorie sources from your fluids enables you to increase fluid intake without the risk of overloading your gut.

How does the gut get overloaded? Here’s the basic math. The standard guidance is that athletes can process 1 gram of carbohydrate per minute, and that with training and the use of mixed sugar sources you can increase this to about 1.4 grams/minute or up to about 90grams per hour. At moderate intensity levels, let’s say riding at 600Kj/hr (which is approximately 600 food calories/hr), replenishing 30% of the calories you burn requires 180 calories of carbohydrate, or 45 grams. Some sports drinks contain 50-60 grams of carbohydrate per bottle. If you were to consume two bottles of those drinks in an hour to meet your fluid needs you would also have to consume 100-120 grams of carbohydrate. There are times when that might be OK, but there are more instance when you’ll want to adjust calorie and fluid intakes independently.

I typically start rides with one bottle of Bonk Breaker Real Hydration (90 carbohydrate calories per bottle), one bottle of water, and either Energy Chews or Muir Energy Energy Gels in my pockets (or both). For longer rides I like the Bonk Breaker Energy Bars (Salted Caramel!!) for taste, texture, and more substantial nutrition with some protein and fat. I look at the Bonk Breaker drink, and others that are similarly low in carbohydrate calories, more as electrolyte drinks (350mg of electrolytes per bottle in Bonk Breaker Real Hydration) for hydration than traditional carbohydrate-rich drinks that aimed to supply fluid, carbohydrate, and electrolytes. I like to have plain water, too, because it is important to drink water when you eat a bar/gel/chew so you can dilute the carbohydrate in your gut for faster digestion.

Slurpee vs. Ice Cubes vs. Room Temperature

This is a subject that has generated a ton of research. From a practical standpoint I believe it boils down to this: Cold water is good. Ice slurry drinks are good for pre-cooling but not better than cold water during exercise. Both options will become room temperature or hot water pretty quickly, so the effect/benefit can be important but relatively short lived. What does all this mean when you walk into a 7-Eleven (or a Wawa, for my Philadelphia friends) a few hours into a hot ride? Fill your bottles with ice cubes and water to put on the bike, and grab a sports drink or sugary drink to drink now. As you continue down the road you’ll have food in your pockets and for a while you’ll have cold water to drink.