What Are the Pros and Cons of Eating Before a Morning Workout? It's All About Your Fitness Goals

Is it necessary to have a meal before your morning exercise?

There is a multitude of opinions floating around the internet about how to get the most out of your workout. There are suggestions about doing fasted cardio, having a meal before exercising, or something in-between. Which is the superior option?

It can be challenging to keep track of the latest, fact-based, dietary and workout trends in the midst of the ever-changing and frequently anecdotal advice found on social media.

The following is an analysis of how skipping a meal before exercise affects the body, who may want to consider fasted cardio, and the types of foods potentially beneficial to consume before a workout.

Choosing not to eat before exercising is often referred to as “fasted cardio.”

Dana Ellis Hunnes, Ph.D., MPH, RD, who is a senior clinical dietitian at UCLA Medical Center, assistant professor at UCLA Fielding School of Public Health, and author of Recipe for Survival, describes fasted cardio as aerobic exercise completed without any food intake (primarily carbohydrates) for a minimum of 8-12 hours before exercising.

Without consciously intending to do cardio in a fasted state, morning workouts without breakfast generally fall into this category.

According to Jen Roper, Ph.D., CSCS, a certified sports nutritionist and associate professor of Health and Human Sciences at Loyola Marymount University, fasted cardio can be performed at any time of the day, provided no food has been consumed in the previous few hours. However, it is typically done upon waking, when the body is naturally in a fasted state.

Exercising without eating first can have an impact on the primary fuel your muscles use for energy during your workout.

In higher intensity exercises, glucose — which is a simple sugar resulting from the breakdown of carbohydrates — is often the primary source of fuel.

The body stores a limited amount of extra carbohydrates in a molecule called glycogen. This stored glycogen can be broken down into usable glucose to provide the energy needed during exercise.

Roper points out that a person is typically in a state of low blood sugar when they are fasted. As a result, the body breaks down stored glycogen more rapidly to provide required energy for the workout. Once the glycogen is used up, the body shifts to using fat as the primary source of energy.

Because of this, fasted cardio is often perceived as a method to increase fat loss, though current research findings are mixed.

Uma Naidoo, MD, a Harvard-trained nutritional psychiatrist, director of Nutritional and Metabolic Psychiatry at Massachusetts General Hospital, and author of the bestseller This is Your Brain on Food and the upcoming book Calm Your Mind With Food, acknowledges that the science behind this belief is more complicated. Roper concurs, pointing out that research findings regarding fat burn in relation to exercising on an empty stomach are inconsistent.

Roper also adds that moderate to high-intensity exercise can be challenging in a fasted state and results in reduced calorie burn overall. Therefore, it might work for some people, but the scientific evidence does not support this approach for everyone.

Results, like many fitness-related issues, can differ from person to person.

While there is some backing for the notion of fasted cardio aiding in fat burning, conflicting evidence points to possible increases in cortisol and inflammation when working out without eating beforehand, both of which could inhibit fat loss and impact health negatively.

Naidoo suggests that without prior food intake, the body may resort to gluconeogenesis (the breakdown of protein for fuel), which can be problematic.

A study conducted in 2015 found that morning exercise following an overnight fast was more effective in reducing body fat compared to exercise without fasting. Nonetheless, participants who fasted before the workout showed increased cortisol levels that could potentially undermine long-term weight loss.

Hunnes states that exercise can cause stress to the body, irrespective of an individual's fueling status. This stress can momentarily increase cortisol levels if the exercise is high-intensity and put strain on the muscles, but these are considered beneficial, short-term stressors that dissipate quickly post-workout and generally enhance health.

While it is clear that exercise can trigger the body's cortisol levels, Roper notes that research findings are murky when it comes to whether fasted cardio can do the same.

That said, a lack of consistency in the research doesn’t mean there aren’t things to be cautious about in terms of fasted cardio stressing the body, said Roper.

According to Roper, fasted exercise is generally safe for most people, but it may lead to side effects.

“Because blood glucose gets depleted during fasting cardio, you can experience some side effects including lightheadedness and dizziness,” she said. “If it is prolonged cardio, you could potentially pass out, so if you commonly experience side effects from low blood glucose, you may want to avoid fasted cardio.”

Hunnes and Naidoo agreed and explained that unless you have a certain medical condition, like diabetes or reactive hypoglycemia, fasted exercise is most likely safe.

“Someone with type 2 diabetes may not do well with fasted cardio first thing when they wake up, as this may heighten insulin resistance,” Naidoo said. “With someone who is taking insulin for the treatment of diabetes management, their situation may be different as well.”

Choosing whether you should eat before a workout can be an individual decision but it also may be a medical decision, in certain cases.

Hunnes explained that children should also have a small meal or snack before harder physical activity because they have a reduced capacity to store glycogen/energy for exercise, and more energy is going towards growth.

For adults, the decision is often based on personal preference, as well as the length and intensity of the planned workout, Roper explained.

“Moderate-to-high intensity workouts and prolonged endurance workouts (more than 1.5 hours) are going to benefit more from eating beforehand,” she said. “It’s difficult to maintain higher intensities once glycogen and blood glucose are depleted, which happens quicker when fasted.”

The other factor you should consider when deciding if you should eat before a workout is your primary fitness goal.

“If you’re exercising for fitness and weight loss, you may want to adjust the timing and what you eat before and after exercising,” said Hunnes. “If you’re training for an event, you may also need to change what, when, and how you eat.”

Hunnes also explained that it’s not only whether or not you eat before a workout that matters—what you eat after a workout plays a key role in helping your muscles and body as a whole recover from your exercise session.

“Once you’ve done damage to the muscle (lifting weights) or worked out the muscles (cardio), you want to replenish the carbohydrate (glucose) stores you’ve depleted and help muscle repair with healthy anti-inflammatory proteins,” she said.

If you do decide to eat before your workout, there are a few things to consider.

“Slow-burning carbohydrates like oats, whole wheat toast, and whole fruit are popular pre-workout foods,” said Naidoo. “The goal is to ensure that you are not feeling too full to get a good workout in, but also that the glucose is still circulating in the system.”

In order to ensure you aren’t too full to work, Naidoo recommends eating 2–3 hours before your workout. If you’re eating 1–2 hours beforehand, opt for a lighter meal.

Hunnes recommends something light and full of carbs, with small amounts of fat and protein, like half a bagel with peanut butter, or a banana with a handful of nuts.

She notes these recommendations apply to healthy individuals without metabolic conditions.

“If you have diabetes or other medical condition that [makes it so] you should eat before, then you should get guidance from your endocrinologist, cardiologist, dietitian, or another medical provider based on your specific needs,” she said.

Roper explained that if you do eat closer to the time of your workout, liquids, and carbs that are not high in fiber or fructose are the best option.

But ultimately, experts agree that the logistics of what you eat and when you eat are personal. What matters most is that people move regularly.

“Whether your cardio is fasted or fed, just do it,” said Roper. “Just remember, most things are a personal preference, and what may work for one person may not work for all.”