Unless you’re an elite athlete, there’s no need to be hypervigilant about how you fuel your workouts. But even casual exercise burns more calories than your body if you were at rest, which means that you might need to eat more in order to support both your workouts and your recovery.
“In a culture that emphasizes ‘eat less, exercise more,’ a lot of people are scared to eat enough [to support their workouts],” says Zoë Schroder, RDN, a nutrition coach and certified strength and conditioning specialist based in Tucson, Arizona. But ultimately, underfueling will undermine your goals and slow your recovery.
Here’s why getting adequate calories is so important, and how to know when you need more calories to fuel your exercise routine.
Why Does Your Body Burn More Calories During Exercise Than It Does at Rest?
“Our body receives the energy it needs in the form of calories, mainly carbohydrates and fat,” says Todd Buckingham, PhD, an exercise physiologist at the Mary Free Bed Sports Rehabilitation Performance Lab in Grand Rapids, Michigan. Carbohydrates break down into glucose and glycogen, while fat breaks down into fatty acids. “From there, these glucose, glycogen, and fatty acid molecules get broken down even further into a molecule called adenosine triphosphate (ATP), which is what provides energy.” (Protein breaks down into amino acids, which also break down to ATP, but this process is less efficient and isn’t used to fuel exercise.)
This process, known as metabolism, happens constantly in your body, even when you are stationary, such as while sleeping in bed or working at your desk. But during exercise, Dr. Buckingham explains, the rate of ATP production increases to support your muscles (which are doing more work than usual), as well as to regulate your body temperature and sustain your increased heart rate and breathing. The more ATP you produce, the more calories you burn.
How Many Calories Do You Burn During Exercise?
According to the Centers for Disease Control and Prevention (CDC), the average 154-pound person will burn about 300 calories per hour during moderate-intensity exercise like walking, golfing, and casual cycling. The same person would burn between 440 and 590 calories after an hour of vigorous exercise like running, swimming, or circuit weight training. For a more accurate estimate on how many calories you burn during a certain activity, you can use a free Physical Activity Calorie Counter, which factors in your body weight, the type of exercise, and the duration.
How Many Calories Do You Need to Support Your Workouts?
To maintain your current weight and keep your energy levels up, you need to eat roughly the same number of calories that you burn each day. For most people who aren’t elite athletes, this happens naturally, without you having to consciously add more food into your day. “Your hunger hormone, ghrelin, ramps up in response to increased exercise as your body's way of telling you you need to eat more,” Schroeder says.
That means that if you’re only doing moderate-intensity exercise — which, remember, burns about 300 calories per hour — a few times per week, there’s probably no need to intentionally up your calories. But if you exercise at a vigorous intensity (running, circuit training, HIIT,), which burns upwards of 500 calories per hour, your ghrelin levels can actually be suppressed post-workout, according to a past study. So, relying solely on your hunger cues could leave you underfueled, Schroeder says.