How to Adjust Your Carb Intake When It Gets Colder

If you’re like me and love the feeling of the warm sun on your skin and sweat dripping as your feet hit the pavement, the end of summer can leave you feeling a bit bummed out. That said, there is something special about running through the cool autumn air with the crunch of leaves under your feet. And, like many other runners, I do run a bit faster and longer when it’s cooler out.

A change in season also means a change in how you should be fueling. As a sports dietitian and lifelong runner, I hear similar struggles from my clients during the summer. A lot of them—maybe you can relate—are just trying to stay on their feet during oppressively humid and hot runs, and the idea of taking in 60 grams of carbs an hour is a hard no. Luckily, the dropping temps can make consuming the right amount of fuel easier—if you know how to adjust. Here’s what you should know.

Why Heat Makes Fueling Harder

“When you run in the heat, your body is focused on cooling itself down,” Kristy Baumann, RD, founder of Marathon Nutritionist in Minneapolis-St. Paul, Minnesota, tells me. “Blood moves toward the skin to help you sweat and cool your core body temperature, which means there’s less blood available to your digestive tract.”

With less blood available in your digestive tract, digestion slows down. That means anything you try to eat or drink—including high-carb gels, chews, or drinks—will sit in your stomach a lot longer. This can lead to poor appetite, nausea, stomach upset, and for some, a panicky feeling and urgency to find the nearest restroom.

Your body will no longer prioritize fueling, Baumann says.

“Then you add in the sweetness or thick consistency of gels, and you’re trying to chew while running, and the whole idea is a big turnoff.”

How to Modify Your Fueling Plan When It Gets Cold Outside

So, summer is a slog for runners in nearly every way. It makes sense that your fueling goal of 30, 60, 90 grams of carbs per hour didn’t happen. But with cooler temperatures and lower humidity, your body can digest better, and your appetite will probably come back.

Before You Run

Aim for 1 to 4 grams of carbohydrate per kilogram of body weight, 1 to 4 hours before a run.

For example, for a 150-pound (60-kilogram) runner who has a run planned for 4 p.m., aim for 4 g/kg, about 270 grams of carbs. That could be a hearty grain bowl, or a sandwich and soup along with a bowl of fruit.

An hour out, your new target is 1 g/kg. For that same runner, the goal is 68 grams of carbs, which could be a fruit smoothie or yogurt parfait.

Midrun

Consuming carbohydrates during a workout is designed to keep your energy levels stay high and prevent you from fully depleting your muscle glycogen stores, which reduces the amount of muscle breakdown.

Here’s what fueling with carbs during your run may look like.

When (and How) to Test New Carb-Fueling Strategies as It Gets Colder

It’s probably not news to you, but athletes training for an endurance event must also train their guts, says Allison Knott, MS, RDN, CSSD.

“This means taking fuel on long runs, rides, or other training sessions that last more than an hour,” Knott says. “This allows time to practice fueling and make modifications as needed.”

If you’re new to fueling during runs, begin with a liquid carb source, such as a sports drink, which delivers carbs, fluid, and electrolytes in one go. Next, try a gel, which is easy to swallow in small amounts while you’re moving. From there, experiment with something you chew, like gummy chews, jelly beans, or even dried fruit.

“Start testing new gels and fueling products as early as possible in your training cycle,” Baumann says. “Practice on shorter, easier weekday runs first to see which products you like the taste and consistency of, so you don’t completely ruin a long run if you find out you can’t tolerate a product.”

Go low and slow. If your goal is 60 grams of carbs per hour for your two-hour run, don’t start there; begin around 30 grams and build up gradually with each run, the same way you’d build mileage for a new race distance, adding a little each week.

“By the time you’re four to eight weeks out from your race, your longest long runs are a great opportunity to practice your full race day fueling plan and use it as a dress rehearsal,” Baumann says.

What to Do If Race Day Happens to Be Warmer Than You Expect?

Picture this: It’s race week, jitters are high, your legs feel rested and ready to move, and then you check the forecast for race day. Bam! Summer is making a return, and temps are not looking good for your fueling plan. Don’t panic; there are a few things you can do.

“The biggest adjustment you’ll need to make is your fluid and electrolyte intake,” Baumann says. “When it’s warm and you’re racing at a higher intensity, you’re sweating more and you have to replace those fluids and electrolyte losses, otherwise things can start falling apart fast. So look at your current fluid and electrolyte plan, and be ready to dial it up in the days leading up to race day and on race day itself.”

But how much should you dial it up? Baumann recommends sweat rate testing ahead of time so you know how much your fluid and electrolyte needs have to change in different conditions.

A sweat rate test measures how much fluid you’ve lost during exercise and can guide you on how much you’ll need to rehydrate.

[(Pre-run weight − Post-run weight) × 16 + fluid consumed] / hours = sweat rate (ounces / hour)

For example:

• Weight before your run: 150 pounds
• Weight after your run: 148 pounds
• Fluids consumed during your run: 20 ounces
• Run duration: 1 hour

You lost 2 pounds, or about 32 ounces of fluid

• 32 ounces lost + 20 ounces consumed = 52 ounces
• 52 ounces / 1 hour = 52 ounces per hour

Your sweat rate in this example is 52 ounces per hour. 

Secondly, “it’s important to continue with the fueling plan and products you’ve trained with to ensure you’re not introducing new products on your race day,” Knott says. The days before and the day of the race are not the time to try a food or drink that’s new to you, no matter the temperatures.

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