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.
“Too much of a calorie deficit can cause individuals to lose muscle mass,” Buckingham says. That’s not a good thing, as muscle mass supports your health by not only making it possible to do physical tasks, but also carrying out basic functions like moving blood through your body and helping you breathe, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Plus, muscle mass actually helps your body burn more calories overall, even at rest, according to a past study.
If you’re trying to lose weight, a small calorie deficit is okay. The Academy of Nutrition and Dietetics (AND) recommends a calorie deficit of no more than 250 to 500 calories per day for active adults. If you notice over time that you’re losing weight and you don’t want to, you could try upping your calorie intake by a few hundred calories per day, Buckingham says. One hundred calories is the equivalent of roughly one medium banana or 1 tablespoon of peanut butter.
5 Signs You Need More Calories to Support Your Workout
Look out for these common signs that you need more calories, so you can ensure you’re eating enough to support your workout routine:
1. Lasting Soreness
“If you notice that you stay sore for a long time after working out, this is a sign of nutritional inadequacy,” Schroeder says. A little bit of soreness is fine, but if it lasts for days, you might need to up your calorie intake as properly fueling is key to muscle recovery.
2. Poor Performance and Fatigue
If you notice that you’re not able to go as hard, fast, or heavy in your workouts as you used to, or if you’re constantly tired outside of your workouts, Buckingham says that this might be a sign that you’re not eating enough.
3. Illness or Injury
Buckingham also warns that not eating enough calories to support your workouts can lead to illness and injury, as both muscle repair and immune function rely on energy and nutrients from food.
Low blood sugar happens when you don’t have enough stored energy. Called hypoglycemia, low blood sugar may result in feeling lightheaded or dizzy, according to Mayo Clinic. This is another sure-fire sign your body needs more calories than you’re taking in.
5. Lost or Irregular Period
Over a long period of time, the combination of exercise and eating too few calories can lead to hypothalamic amenorrhea, a deficiency of the reproductive hormone estrogen. A literature review published in February 2019 in Seminars in Reproductive Medicine explains that hypothalamic amenorrhea can lead to lost or irregular periods, as well as irreversible bone loss and an increased risk of cardiovascular disease. As this is more serious than other symptoms, it’s best to speak with your doctor.
Tips for Increasing Your Calorie Intake
The good news is that upping your calorie intake is relatively simple. Schroeder recommends adding a snack or two in between meals that contains a balance of protein, carbohydrates, and fat. “Carbohydrates are your body’s main fuel during exercise, so it’s important to replenish them afterwards,” Schroeder says. “Protein is essential for building and maintaining healthy muscles, and fat is important for vitamin absorption, hormone function, and overall health.” Some easy snacks that Schroeder suggests are peanut butter and banana, fruit and yogurt, or hummus and crackers. Portion size will depend on both your goals and how many calories you’re burning during a workout. If you’re aiming to eat 300 calories, you can get that from one medium banana and 2 tablespoons of peanut butter.
If snacks aren’t your thing, or if you need more calories than snacks can provide, Schroeder also recommends adding more healthy fats to your meals, since fat has more than double the calories (9 calories per gram) compared with protein and carbs ( 4 calories per gram), according to the Cleveland Clinic. “Things like avocado, olive oil, and peanut butter can increase calories without adding too much additional volume,” she says. Ultimately, eat healthy, whole foods to feel energized during workouts and throughout the day.