Can I Lose Fat While Training for a Half Marathon?

The Smart Way to Combine Endurance Training with Fat Loss Without Burning Out

Why This is a Common but Tricky Goal

It’s a classic combo goal: you sign up for a half marathon to get fit, drop some fat, and maybe even bag a personal best while you’re at it. Seems like a no-brainer, right? Run more, eat a bit less, and the fat should melt away. But in reality, trying to lose fat while training for a half marathon is a bit like trying to pat your head and rub your stomach at the same time – possible, but it takes strategy.

Endurance training demands fuel. Fat loss requires a calorie deficit. Balancing the two without running yourself into the ground or ending up hangry on your Sunday long run? That’s the tricky bit. But with the right approach, it can absolutely be done.

Quick Answer Summary

Yes, you can lose fat while training for a half marathon, but it requires:

• A moderate calorie deficit (not extreme dieting!)

• Prioritising protein and nutrient density

• Smart strength training

• Avoiding common mistakes like overtraining and under-fuelling

• Adjusting your plan week to week based on energy levels, recovery, and performance

The Physiology of Fat Loss + Endurance

Fat loss boils down to energy balance: burn more calories than you consume. But when you're training for a half marathon, your body is already under stress from frequent running sessions. Long runs, tempo runs, speed work – they all deplete glycogen, elevate cortisol (your stress hormone), and increase your recovery needs.

Too large a calorie deficit in this phase can mess with recovery, suppress your immune system, and potentially lead to lean muscle loss – not what we want. Also, endurance training mainly burns a mix of fat and carbs, but the intensity of your runs will shift that balance. Easy, longer runs favour fat oxidation, while harder efforts rely more on glycogen (carbs).

So, the key? Train smart. Recover well. Fuel properly. And create just enough of a deficit to encourage fat loss without compromising performance.

Nutrition Adjustments for Fat Loss + Performance

1. Moderate Calorie Deficit (250-500 kcal/day)

Avoid slashing calories. A small deficit allows fat loss while maintaining performance. Use a calculator to estimate your Total Daily Energy Expenditure (TDEE) with your current training load, and reduce intake slightly from there.

2. Protein is Non-Negotiable

Aim for 1.6–2.2g of protein per kg of body weight daily. Protein helps retain muscle mass during a deficit and improves recovery from runs. Include high-quality sources like:

• Eggs

• Chicken, turkey, lean beef

• Greek yoghurt, cottage cheese

• Lentils, tofu, tempeh

3. Fuel Around Runs

You don’t need to be low-carb to lose fat. In fact, carbs before and after key workouts (long runs, intervals) can improve performance and preserve lean muscle. Think of fuelling like bookends to your sessions:

• Before: A banana or toast with honey

• After: Rice and lean protein, or a smoothie with fruit and whey

4. Watch Your Weekend Calories

Long runs can trigger big hunger spikes and "I earned this" thinking. Track intake loosely (not obsessively) and stay mindful of weekend splurges undoing your weekly deficit.

Strength Training Integration

Adding 2 sessions of full-body strength work each week is a game changer.

• Preserves lean mass in a deficit

• Reduces injury risk from repetitive running motion

• Improves stride efficiency and posture

Focus on compound lifts:

• Squats, lunges

• Deadlifts, RDLs

• Push-ups, pull-ups

• Planks, rows

Keep reps moderate (6–12), rest properly between sets, and ideally place sessions on non-running or easy run days. Think of it as insurance for your body.

Mistakes to Avoid

1. Overtraining

Stacking hard runs, strength training, and a calorie deficit? Recipe for burnout. Listen to your body. If energy crashes, sleep suffers, or mood tanks, dial things back.

2. Under-Fuelling

Skipping meals or cutting carbs drastically can derail performance, recovery, and mood. Remember: food is fuel, not the enemy.

3. Scale Obsession

Weight may fluctuate with glycogen, water retention, and inflammation. Progress pics, how clothes fit, and performance markers often tell a better story than the scale.

4. Neglecting Recovery

Prioritise 7–9 hours of sleep, hydration, mobility work, and rest days. Recovery drives adaptation and fat loss just as much as training.

Case Study: George, 33, London

George, a marketing manager from Clapham, wanted to lose 6kg while training for his first half marathon. He ran 4x/week, added 2 strength sessions, and followed a high-protein diet at a 300-calorie deficit.

Key wins:

• Dropped 5.8kg over 14 weeks

• Maintained strength and energy

• Ran his half in 1:49:33

• Reported improved confidence, sleep, and energy levels

His secret? Consistency, not perfection. He still had the odd pint or burger, but stayed consistent with training, sleep, and fuelling around runs.

FAQs

• Should I eat in a deficit while training for a half marathon? 
  • Yes, but keep it small (250–500 kcal/day). Focus on nutrient density and time your carbs around workouts.
• Won’t I lose muscle in a deficit? 
  • Not if you’re eating enough protein and lifting weights. Running alone won't protect muscle mass.
• Do I need to go low-carb to lose fat? 
  • Nope. In fact, endurance athletes typically perform better with moderate to high carbs. Just keep portions appropriate to your goals.
• How long will it take to see results? 
  • Expect 0.5-1kg fat loss per week if things are dialled in. Be patient and monitor performance to ensure you're not overdoing it.

Final Thoughts: Yes, You Can Have Your Cake (and Run It Off)

Losing fat and running a half marathon aren’t mutually exclusive. But you’ll need a plan, patience, and an understanding of how to fuel the machine while trimming the body fat.

If you're after a bit more guidance on structuring your training, dialling in your nutrition, or just having someone in your corner keeping you on track, click here to find out more about coaching options. We’ll build a plan that works for your life and goals.

Check out our related blog | Best Strength Exercises for Runners Who Want to Avoid Injuries