6 Clues You May Be Losing Muscle During a Diet

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LOSING WEIGHT IS never easy. Between changing the way you eat and stepping up your workouts, it often requires a major lifestyle shift. The usual aim is to shed body fat while preserving or building muscle. But sometimes, the opposite happens: you lose muscle instead of fat, which is far from ideal.

“It is bad to lose muscle instead of fat, because muscles are the key players in body movement and function,” says Gerardo Miranda-Comas, M.D., Assistant Professor of Rehabilitation Medicine at the Icahn School of Medicine at Mount Sinai. “With loss of muscle mass, strength and endurance are affected negatively, leading to decreased functional performance.”

That said, muscle should not be the first thing your body taps into during healthy weight loss. “A person who is attempting to lose weight by not eating may lose weight in muscle first before fat,” he says.

Here’s why: the body prefers carbohydrates, or glucose, for energy first. If those aren’t available, it turns to glycogen, the stored form of glucose found in the liver and muscles, Miranda-Comas says.

So how can you tell whether you’re dropping muscle rather than fat? Watch for these six signs.

1. Your workouts feel tougher than usual.

This may sound obvious, but exercise can start to feel much harder, and you may even dread going at all.

“You’ll notice less strength in the gym. The weight you used to be able to do for reps may decrease or you may not be able to get as many reps as you once did for each set,” says Spencer Nadolsky, D.O., author of The Fat Loss Prescription.

2. Everyday tasks leave you feeling weak.

Muscle loss is not something you only notice during exercise. It can show up when you climb stairs, carry grocery bags, or lift luggage.

“Inadequate nutrition can lead to a decrease in muscle, which may lead to impaired function,” says Dr. Miranda-Comas. “This is usually caused by an energy deficiency and possible overtraining.”

“In the very active individual who is losing weight along with a decrease in performance, we must consider overtraining,” says Dr. Miranda-Comas.

3. Your body fat percentage stays the same.

If the scale is moving down but your body fat percentage is not changing, that can be a sign that muscle is being lost.

“Your body won’t shape the way you want. You’ll notice shrinking circumferences, but the pinch-able fat is the same,” says Dr. Nadolsky.

4. The weight is dropping too quickly.

Fast results may feel exciting, but they are not usually a good sign for muscle retention unless you begin with a significant amount of fat to lose.

“The more fat you have, the more likely you'll lose more fat than muscle when losing weight,” says Dr. Nadolsky.

Rapid weight loss is also rarely sustainable.

“Weight loss requires a long period of time and being patient—it’s a marathon and not a sprint. People should (only) lose 1-2 pounds per week,” says Delbridge.

5. Your training never seems to improve.

It makes sense that progress is harder when you are tired, but if you can never increase the weight you lift, that may point to muscle loss, according to Albert Matheny, C.S.C.S., R.D., founder of Soho Strength Lab. “A lot of factors affect performance, but not seeing progress in training is a good sign you’re not hitting your body’s needs,” he told Women's Health.

6. You feel tired all the time.

Constant fatigue can be a sign that you are not eating enough. When calories and carbohydrates are too low, your body may start using muscle to access glycogen for energy.

To lose weight without sacrificing muscle, aim for roughly one pound per week, which typically means a deficit of about 200 to 500 calories a day depending on your activity level. A registered dietitian or doctor can help you determine a healthy calorie deficit for your needs.

Emily Shiffer has worked as a writer for over 10 years, covering everything from health and wellness to entertainment and celebrities. She previously was on staff at SUCCESS, Men's Health, and Prevention magazines. Her freelance writing has been featured in Women's Health, Runner's World, PEOPLE, and more. Emily is a graduate of Northwestern University, where she majored in magazine journalism at the Medill School of Journalism and minored in musicology. Currently residing in Charleston, South Carolina, Emily enjoys instructing barre, surfing, and long walks on the beach with her miniature Dachshund, Gertrude.

Melissa Matthews is the Health Writer at Men's Health, covering the latest in food, nutrition, and health.

Cori Ritchey, C.S.C.S., is the fitness editor at Women's Health, as well as a certified strength and condition coach and group fitness instructor. She’s reported on topics regarding health, nutrition, mental health, fitness, sex, and relationships for several years. You can find more of her work in Men’s Health, HealthCentral, Livestrong, Self, and others.