Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
You’ve finally committed to those workouts, swapped chips for chickpeas, and the number on the scale is heading south. But here’s the big question: Are you actually losing fat—or are your muscles waving goodbye too?
It’s a crucial difference. Losing fat means your body’s getting leaner, healthier, and stronger. But losing muscle? That’s not the kind of weight you want to shed. Studies show that muscle mass is linked to better metabolism, longevity, and even mental health. So if your clothes are looser, but you're also struggling to lift your usual grocery bags, it's time to tune in.
Read on to spot the telltale signs you're dropping fat (not muscle) and learn how to keep those gains while torching the fluff.
Muscle isn’t just about looking toned or flexing at the beach. It plays a massive role in keeping your body functioning optimally.
Muscle mass boosts your resting metabolic rate (RMR) or the number of calories your body burns just to stay alive. Plus, maintaining lean muscle helps stabilise blood sugar, supports joint health, and fights age-related muscle loss (a.k.a. sarcopenia), which starts as early as your 30s.
In short? Keep the muscle. Ditch the fat.
You want to watch for these signs if your weight loss plan is secretly stealing your strength:
Sudden drop in strength: Struggling to lift the weights you smashed last week? A sharp dip in strength could mean muscle loss.
Constant fatigue or low energy: Muscle helps regulate energy levels. When it starts disappearing, your get-up-and-go might just get up and leave.
Noticeable loss in muscle size: If your arms and legs look smaller but not more defined, that’s a red flag.
Slower recovery after workouts: Feeling sore for days? Losing muscle can impair recovery time and increase injury risk.
Feeling weaker during everyday tasks: Can’t carry the laundry basket like you used to? It might be more than just a lazy day.
Flabby or soft appearance despite weight loss: Fat loss = firmness. Muscle loss = mush. If you're getting softer, it’s likely not just fat that’s going.
Rapid weight loss without body definition: Losing weight too quickly (more than 1 kg a week) often includes muscle mass.
Avoid these classic blunders if you want to hang on to those gains:
Skipping strength training: Cardio alone won’t cut it. Resistance training is key to preserving muscle mass.
Eating too few calories: Eating like a bird? Your body might burn muscle for energy, especially if you're under 1,200 calories a day.
Not getting enough protein: Protein is the building block of muscle. Studies show that 1.6–2.2g per kg of body weight supports muscle retention during weight loss.
Overdoing cardio workouts: Excessive cardio without strength training can lead to muscle breakdown, especially if you're in a calorie deficit.
Ignoring rest and recovery: Muscle growth happens after your workouts. Skipping rest sabotages gains.
Following crash diets: Crash diets = quick results + long-term damage. They’re notorious for draining muscle mass.
Losing weight too quickly: Slow and steady really does win the fat loss race. Rapid weight loss often comes with water and muscle loss.
Training without a structured plan: Random workouts? Random results. A balanced plan ensures you hit all the right muscles and avoid overtraining.
Wondering if you're on the right track? Here are the feel-good, fat-loss-friendly signs:
Your jeans are suddenly loose, and that clingy top finally flatters, without the scale budging. That’s because fat takes up more space than muscle.So when your clothes fit better but your weight stays the same, it’s a sign you’re dropping fat and keeping that precious lean mass.
Pumping heavier weights or powering through more reps lately? That’s not just good vibes; it means you're preserving or even building muscle while losing fat. Fat loss that comes with strength gains is a surefire win.
That sculpted look? It's the result of fat melting away while your muscle stays put. Toning is just code for revealing muscle underneath and it's a clear sign you’re losing fat, not muscle.
If the measuring tape says smaller but the scale says ‘meh,’ don’t panic. Muscle is denser than fat, so you can lose fat, gain (or retain) muscle, and still weigh the same—but look noticeably leaner.
You’re not dragging yourself through the day or craving five naps. Instead, your energy's solid. That’s a green flag that you're fuelling properly, maintaining muscle, and losing fat the right way.
If the number on the scale is drifting down slowly, say around 0.5 to 1 kg a week, you’re likely losing fat, not muscle. Rapid drops often signal water or muscle loss, not long-term results.
Still crushing your workouts? That’s a fantastic sign that your muscles are hanging around while the fat takes a hike. Muscle loss usually shows up as poor performance in the gym.
DOMS (that lovely post-leg day pain) not hanging around as long? Your body’s adapting and repairing better. It’s proof that your muscles are being looked after, not broken down.
That cheekbone pop or jawline you haven’t seen in ages? Often, fat loss starts from the top down, so a slimmer face is one of the first signs things are moving in the right direction.
Losing centimetres around your waist, even if the rest of you seems unchanged, is a classic sign of fat loss, especially visceral fat, which clings to your belly and organs.
Better body composition and regular training often come with deeper, more restful sleep. One study even linked fat loss to improved sleep quality and duration.
A flatter stomach isn’t just fat loss. It could be less bloating too. Cleaner eating, better hydration and improved digestion often go hand-in-hand with fat loss.
If your body fat percentage is dropping, whether via skinfold calipers, DEXA, or smart scales, it’s a direct indicator that you’re burning fat, not muscle.
Noticing more shape in your arms, legs, or abs? That’s muscle showing through as the fat layer shrinks. You’re revealing, not losing, your gains.
You’re eating balanced meals, feeling full, and not raiding the snack drawer every hour. That’s often because higher protein intake supports muscle and satiety during fat loss.
Not all weight loss is good weight loss. Rapid weight loss might seem appealing, but it often means you're losing muscle, not just fat. Dr Nick Fuller explains why that’s a problem, and how the IWL method helps you lose fat while keeping your muscle strong and intact.
Want to be 100% sure your weight loss is all fat, no fluff? Here’s how to lock it in:
At least 2–4 times per week. Focus on compound lifts (squats, deadlifts, presses) to maximise muscle retention.
Aim for 1.6–2.2g per kg of body weight. Think eggs, chicken, tofu, legumes and Greek yoghurt.
Go for a moderate deficit, like about 500 calories below maintenance, for sustainable fat loss.
Use a tape measure or progress photos to track changes in body shape and size.
Aim for 7–9 hours of sleep and active rest days. Sleep is when the magic happens.
Weekly snapshots or gym logs help you see changes that the scale can’t.
Both dehydration and chronic stress can mess with fat loss and muscle retention.
Losing fat without sacrificing muscle isn’t just possible. It's THE goal. Your body will thank you with better strength, metabolism, and all-round vitality. So train smart, eat well, and don’t be fooled by the scale. If your jeans are looser, your workouts are stronger, and your reflection’s looking sharper, you’re absolutely smashing it.
Want to lose fat without sacrificing muscle?
Download our free fat-loss resource guide to learn how to protect your lean muscle while shifting body fat, backed by science, not fads. It’s time to ditch the guesswork and take control of your body transformation. Get the guide now.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.