Is It Ever OK To Work Out On An Empty Stomach? The Answer May Surprise You.
Whether you’re a regular at your local gym or are just getting back into working out consistently, it can be tricky to know if and when you should eat before your workout.
Maybe your preferred time of day to work out is the morning and you just want to get going before anything can derail you. Or perhaps you think that eating something before working out will make you feel nauseated. Maybe you want to lose weight and you would rather skip a pre-workout snack because you believe it will impact your calorie deficit.
These are all valid reasons someone may want to do a “fasted workout,” aka exercise on an empty stomach. But according to sports dietitians, fasted workouts aren’t always safe or effective.
Part of your answer depends on the type of workout you plan to do.
According to sports registered dietitian (RD) Michael Reavis Jr., whether or not a fasted workout is safe and effective depends on the type of workout you’re going to do. “The best workouts to do in a fasted state are low-intensity cardiovascular exercises, such as walking, jogging, light swimming, yoga, cycling or light- to medium-intensity weight training, all for up to 75 minutes,” he told HuffPost.
Reavis explained that when the body is in a fasted state during a 75-minute workout, it taps into the body’s glycogen stores. Glycogen is a form of glucose the body uses for energy. “We are able to exercise fasted due to glycogen and the body’s ability to use stored body fat as energy,” Reavis said. “However, when exercising at high intensities — 85% of max heart rate — it becomes challenging for the body to meet the energy demands with body fat, because fat metabolism is slower than carbohydrate metabolism.”
Fasting can actually make your workout less effective.
Sports registered dietitian nutritionist (RDN) Julia Long also told HuffPost that not eating before a workout is OK for low-intensity workouts and for workouts lasting about an hour, but it’s important to fuel properly before anything more intense or longer.
“The issue with fasted workouts lasting longer [than 75 minutes] is that you can have less energy output during the workout due to a lack of fuel, which could affect your endurance and performance outcomes,” she said. This means your workout will be less effective because you won’t have the energy to give it your all.
If you don’t eat before an intense workout (such as heavy weight-lifting or any workout lasting longer than 75 minutes), Long shared that not only will your workout not be as effective, but it can cause more harm than good. “During intense exercise, your body may start breaking down muscle tissue for energy if glycogen is low, especially if you’re in a fasted state,” she said.
Long added that fasted high-intensity workouts can increase cortisol levels, the stress hormone, which could make recovery harder — another reason to avoid it.
Even if your primary health goal is weight loss, sports RDN Grace Kelley told HuffPost that it’s in your best interest to eat before an intense or long workout.
“Fueling with the right foods can actually improve your fitness because you’re able to exercise longer with higher intensity,” she said. “Weight loss requires a calorie deficit, but cutting too many calories can actually lead to a slower metabolism, higher risk of illness and injury, fatigue and bone disorders.”
To sum it up: If your workout is less than 75 minutes or involves light to medium weights, you’re OK to do it fasted. But if you’re lifting heavy weights or plan on working out more than 75 minutes, you need to eat something first.
Here’s when and what to eat before you work out.
If you’re planning on doing an intense or long workout and want to eat something beforehand, timing matters. Eat too far in advance, and you won’t have the nutrients readily available to fuel you, but eating immediately before your workout could make you feel nauseated. According to Kelley and Long, the sweet spot is eating between 30 minutes to one hour before your workout. This gives the body time to digest the food, converting the nutrients into fuel you can use.
When you’re planning your pre-workout meal or snack, Long said to make sure it has carbohydrates, protein and unsaturated fats — all nutrients the body uses as fuel. Kelley emphasized the importance of carbs. “The more intense and longer a workout is, the more carbohydrates you need,” she said. Reavis agreed and recommended aiming for between 30 and 45 grams of carbohydrates pre-workout.
If you’ve never eaten before a workout before and are worried about how it will impact your stomach, Kelley recommends starting with easy-to-digest foods like bananas, graham crackers, toast or applesauce.
Long shared that other foods to integrate into your pre-workout meal or snack include oatmeal, whole grain bread, Greek yogurt, lean turkey meat, a protein shake and nut butter.
All three sports dietitians said that hydration matters, too. Even if you are doing a fasted workout, Long said it’s important to hydrate properly before, during and after you exercise. Otherwise, your body and brain won’t be able to function properly.
To avoid feeling like you have a belly full of water during your workout, Long recommends hydrating gradually leading up to your workout instead of having a large amount of water directly before you exercise.
“Shoot for consuming half your body weight in ounces of water daily,” she said. Reavis added to this, recommending drinking 8 ounces of water before a workout and continuing to drink during and after the workout, as needed. If your workout is going to be longer than an hour, Kelley recommends hydrating with a sports drink with carbohydrates and electrolytes during and after your workout.
Remember, fasted workouts are only OK if they’re less than 75 minutes. Just like a car needs to be fueled properly for a long drive, the body needs to be fueled properly for a long workout. Otherwise, you won’t be able to keep going.
