We’ve all heard that exercise is good for us, and it’s undeniably true. Research shows time and time again that the perks of staying active are seemingly endless: exercise helps to lower blood pressure, improve cholesterol levels, and reduce inflammation throughout the body. It’s also a key factor in managing weight and helps our bodies use insulin more effectively. Aside from keeping you at a significantly lower risk of developing conditions like heart disease, type 2 diabetes, obesity, and even some types of cancers, exercise can even lift your mood and help you sleep more soundly.

But here’s a question that sparks a ton of debate: Should you fuel up before hitting the gym, or is that whole “empty stomach workout” (you might’ve heard it called “fasted cardio”) the real secret weapon? The truth is, it’s not a simple yes or no answer because the connection between exercise, food, and how our bodies use energy is complex. Let’s break it all down.

Fueling your body with carbs and fats

To understand the fasted vs. fed debate, it helps to know a bit about how your body uses fuel in the first place. The food you eat provides three main macronutrients: carbohydrates, fats, and protein. Your body primarily uses carbohydrates and fats for energy.

Carbohydrates (carbs) are your body’s preferred, quick energy source. Carbs are broken down into glucose, which your cells use for fuel. Extra glucose is stored as glycogen in your muscles and liver.

Fats are a more long-lasting energy source. When glucose and glycogen run low (like during a fast or a long workout), your body starts breaking down fat for fuel. When you’re fasting – for example, overnight while you sleep-, your body uses up its stored glycogen. If glucose gets really low, your liver starts making ketone bodies from fat. This is called ketosis – a state where your body shifts from burning primarily carbs to burning primarily fat. This ability to switch between fuel sources is called “metabolic flexibility.”

How exercise intensity affects fuel use

Your body uses both carbs and fat during exercise, but the mix depends on how hard you’re working: Low-intensity exercise (leisurely walking, light chores): Your body primarily burns fat. Moderate-intensity exercise (brisk walking, mopping): You burn a mix of fat and carbs. High-intensity exercise (running, intense fitness classes): Your body relies mostly on carbs for quick energy. “Fat oxidation,” or burning fat for fuel, is highest during lower-intensity activities and when your body is low on glucose and glycogen.

Fasted vs. fed: What the research says

So, how does eating (or not eating) before exercise affect your workout? Here’s a quick summary of what research suggests:

Fax oxidation: Here’s where fasted exercise often gets the spotlight. When you work out before eating, your body tends to burn more fat for fuel. Studies back this up, showing noticeably higher fat-burning rates during those empty-stomach sessions.

Exercise performance: For quick workouts (think under an hour), whether you eat or not probably won’t make a huge difference in how you perform. But, if you’re going longer, having some food beforehand can often give you that extra endurance boost.

Blood sugar control: Exercising on an empty stomach can make your body more sensitive to insulin and keep your blood sugar lower, and that increased fat burning can even last for hours after your workout. But, eating before you exercise helps your muscles soak up glucose (sugar) fast, which also lowers blood sugar.

Daily calorie intake: Some research hints that working out fasted could actually lead you to eat fewer calories overall throughout the day. One study found that men who skipped breakfast before exercising ended up eating significantly less later on, compared to days when they had a morning meal.

Both fasted and fueled workouts have their perks. There’s no magic bullet, no single “best” way for everyone. It really comes down to you – your goals, what you enjoy, and how your body feels. The key is to experiment. Try both approaches and see what makes you feel energized and strong!

References: 1. https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/is-exercise-best-served-on-an-empty-stomach/A04D0203FA9EE39985F0E8E8D2162D10 2. https://onlinelibrary.wiley.com/doi/abs/10.1111/sms.13054 3. https://bmjopensem.bmj.com/content/8/1/e001206.abstract 4. https://www.nal.usda.gov/legacy/fnic/macronutrients 5.https://onlinelibrary.wiley.com/doi/abs/10.1111/sms.13054https://onlinelibrary.wiley.com/doi/abs/10.1111/sms.13054