What You Should Know About Weight Training on a Calorie Deficit

Strength training can pose a dietary challenge. If you want to lose weight, you need to create a calorie deficit. That means you have to burn more calories than you take in each day. But to gain muscle, you need to eat in a calorie surplus, which means eating more calories than it takes to maintain your weight.

This may sound like a challenge if you’re lifting weights while trying to lose weight. But strength training while maintaining a calorie deficit can be a good way to protect your muscles while losing fat.

Where Your Body Gets Fuel During Exercise

To understand how to strengthen muscles while losing weight, it’s important to know how your body gains energy.

When we exercise, your body turns to carbohydrates and fat for its main fuel sources. How much your body uses of each depends heavily on context, such as the duration and intensity of exercise, according to the International Journal of Environmental Research and Public Health. If your body doesn’t have enough carbs and fat to pull from, it may depend more on protein for energy. This may lead to the breaking down of muscle tissue.

If you create a calorie deficit, your body likely has less carbs and fat for energy. This can help you lose weight and shed fat during exercise, including weight training. But it does increase the likelihood of losing muscle mass as well.

How Protein Plays a Role

Lifting weights, however, can help you preserve muscle mass. It can act as a signal to retain and even gain muscle if paired with the right diet, according to the University of Maryland Medical System.

The key is to track your protein intake as well as the magnitude of your calorie deficit.

In your body, protein is broken down into amino acids, which are like building blocks. Your body reassembles those amino acids to build muscle and other tissues, helping you recover after a workout. But if you don’t eat enough, your body doesn’t have the building blocks needed to repair existing muscle and build new tissues.

The recommended daily allowance for protein is 0.8 grams (g) per kilogram (kg) of body weight — or 0.36 g per pound — to avoid a deficiency, according to the National Academies Press. When you’re in a caloric deficit, however, you may need more protein to prevent muscle loss. Athletes and people who lift weights may want to increase that to 1.4 to 2 g per kg or more, according to the Journal of the International Society of Sports Nutrition.

Taking in more protein during resistance training can build fat-free muscle mass, according to a research review in the Strength and Conditioning Journal. You may not necessarily lose weight, but you may lose weight from fat and gain it from muscle.

“Muscle is more dense than fat and takes up less volume, [so] you may look smaller and leaner, but your weight maybe stays the same,” says Carolina Araujo, a New York–based strength coach.

You can even gain some muscle while in a caloric deficit, especially if you’re new to exercise.

If you’re interested in losing weight without losing muscle mass, keep an eye on your calorie deficit. According to a meta-analysis in the Scandinavian Journal of Medicine and Science in Sports, keeping your calorie deficit at less than 500 calories per day may help ensure that your body has enough fuel without turning to proteins.

Should You Adjust Your Weight-Training Routine?

Your weightlifting routine doesn’t necessarily need to change if you're in a calorie deficit, Araujo says.

You can continue whatever program you were already on. But if gaining strength is your goal, you would still need to train with progressive overload, or increasing your weight, reps, or sets over time.

“Progressive overload in a calorie deficit is possible, but it’s more challenging with lower calories,” Araujo says. “Since you’re in a deficit, your body should, theoretically, pull from its fat stores for energy.”

That’s why it’s probably more productive to aim for fat loss, rather than weight loss. If it seems like you’re not losing weight while strength training in a calorie deficit, it may be because you’re actually gaining muscle while losing fat.