Is it better to workout on an empty stomach? The real science behind fasted exercise

Ever woken up and thought, fasted workout will burn more fat? You’re not alone. Millions of people swear by skipping breakfast before a morning run or lift. But is it really better? Or is this just another fitness myth that sounds smart but doesn’t deliver?

What happens when you workout on an empty stomach?

Your body runs on fuel-mostly glucose from carbs and stored fat. When you haven’t eaten for 8-12 hours (like after sleep), your liver glycogen stores are low. That means your body turns to fat for energy. Sounds ideal, right? But here’s the catch: your body doesn’t care if you burn fat during the workout. It cares about what happens the rest of the day.

A 2023 study from the University of Bath tracked 20 healthy adults doing the same 60-minute cardio session either fasted or after eating. Both groups burned nearly the same total calories. But the fasted group had higher fat oxidation during the workout. Sounds like a win? Not so fast. The next day, those same people ate more. Their bodies compensated. Net fat loss? Zero difference.

When you train fasted, your body also breaks down muscle for energy more easily. That’s because without amino acids from food, your system can’t protect muscle tissue. That’s bad news if you’re trying to build or keep lean mass. You might lose fat-but you’ll lose strength too.

Who actually benefits from fasted workouts?

Not everyone. Fasted training works best for a small group: people doing low-to-moderate intensity cardio for under 60 minutes, who aren’t focused on muscle gain, and who feel fine without food.

For example, someone walking briskly for 45 minutes before breakfast might feel energized and not hungry afterward. That’s fine. But if you’re lifting heavy, doing HIIT, or training for endurance, you’re setting yourself up to crash. Your performance drops. You feel sluggish. Your form suffers. And that increases injury risk.

Research from the Journal of the International Society of Sports Nutrition found that athletes who trained fasted had 12% lower power output during sprints and 18% slower recovery times compared to those who ate a small meal beforehand. That’s not a minor difference-it’s the difference between hitting your goals and hitting a wall.

What should you eat before a workout?

You don’t need a big meal. Just enough to fuel your session without weighing you down. A banana, a spoon of peanut butter on toast, or a small protein shake 30-45 minutes before training does the trick.

Here’s what works for most people:

• 15-20g of easily digestible carbs (banana, oatmeal, rice cake)
• 5-10g of protein (Greek yogurt, whey, egg)
• No heavy fats or fiber (they slow digestion)

This combo gives you energy without bloating. It also signals your body to preserve muscle and tap into fat stores more efficiently-without the crash of a fasted state.

And yes, you can still burn fat. Your body doesn’t need to be starving to use fat as fuel. It does it all day long, even after you eat. The key isn’t starving yourself-it’s creating a consistent calorie deficit over time.

What about intermittent fasting and morning workouts?

Intermittent fasting isn’t the same as skipping a pre-workout meal. If you’re eating within an 8-hour window and your workout falls at the end of your fast, that’s different than never eating all morning.

Some people do well with this setup-especially if they’re used to it. But it’s not magic. If you’re not losing weight or gaining strength, the problem isn’t your timing. It’s your total calories and protein intake over the day.

One 2024 meta-analysis of 17 studies found no significant difference in fat loss between people who fasted before exercise and those who ate, as long as total daily calories and protein were matched. The timing didn’t matter. The consistency did.

When fasting before exercise backfires

It’s not just about performance. Fasted workouts can mess with your hormones. Cortisol-the stress hormone-rises naturally in the morning. Add exercise on empty stomach, and it spikes even higher. That can lead to:

• Increased appetite later in the day
• Cravings for sugar and carbs
• Slower recovery
• Disrupted sleep

Women are especially sensitive to this. Studies show that women who train fasted regularly report more fatigue, irregular periods, and mood swings. Their bodies interpret the stress as a threat-and shut down non-essential functions, including fat loss.

If you’re a woman, over 40, or recovering from burnout, fasted training is more likely to hurt than help.

Real-world examples: What works for real people

Let’s say you’re a 35-year-old office worker in Adelaide who runs 5K every morning. You’ve tried fasting. You felt dizzy halfway through. Your legs felt heavy. You gave up.

Then you started eating a piece of toast with almond butter 30 minutes before. Same distance. Same time. But now you finish strong. You sleep better. You don’t crave junk after work.

Or you’re a 28-year-old trying to build muscle. You lift weights at 6 a.m. You skip breakfast because you heard it boosts fat loss. After three months, your strength stalled. You lost 2 kg of muscle. You didn’t lose an ounce of fat.

You started eating a protein shake before your session. Two months later, you added 1.5 kg of muscle. Your body fat dropped by 1.8%.

The difference wasn’t the fast. It was the fuel.

Bottom line: It’s not about empty stomachs. It’s about consistency.

The best workout is the one you can do consistently, with energy, and without regret. If you feel great fasted, and you’re not losing muscle or energy, keep doing it. But don’t believe the hype that it’s better.

If you’re tired, weak, or hungry during your workout, eat something. It’s not cheating. It’s smart.

Forget the myth. The real secret to fat loss and fitness isn’t when you eat. It’s how much you eat over the week, how much protein you get, and whether you show up day after day.

Your body doesn’t care if you trained on an empty stomach. It cares if you showed up. And if you can keep showing up, you don’t need to fast to win.