When it comes to weight loss, some people diet, some exercise, and others combine both. But pairing diet with exercise doesn’t just boost your results—it helps protect what you don’t want to lose: lean muscle.

Weight loss happens when your body burns more energy than it takes in. During a calorie deficit, the body draws on stored energy, but it doesn’t burn fat exclusively. Research shows that 20% to 40% of the weight lost during dieting can come from lean muscle mass.

This happens because when energy is scarce, the body begins breaking down muscle protein to convert its amino acids into glucose. The process accelerates when:

Losing muscle while dieting changes your metabolism in ways that make long-term weight maintenance harder. Muscle is metabolically active—it burns calories even at rest. Muscle is metabolically active—it burns calories even at rest.

One pound of muscle burns roughly 6 calories per day at rest, increasing to about 9–10 calories with normal movement. The number may seem small, but over time this contributes meaningfully to daily energy expenditure.

Aggressive dieting, which can create energy deficits of 500–1500 kcal per day, leads to rapid weight loss but also greater loss of lean tissue. Correspondingly, for every 1 kilogram of body mass lost, basal metabolic rate (BMR)—the energy your body uses at rest—drops by roughly 15%. 

Less muscle means a lower BMR, which makes future weight loss and weight maintenance more challenging. It’s also important to note that even with exercise, a very large calorie deficit will still cost you some lean mass. A severe deficit signals the body to conserve energy, and muscle is expensive to maintain.

The same principle applies to hair health during aggressive dieting. Hair follicles are highly sensitive to energy and nutrient availability, and when calories drop too low, the body prioritizes survival over growth. Reduced protein intake, micronutrient deficiencies, and hormonal shifts can push hair into a shedding phase, leading to thinning or increased hair loss—often months after the diet ends.

Hair thinning with age is often blamed on hormones or genetics, but a newly discovered scalp buildup could be the real culprit. 

This simple home remedy helps clear it out and supports healthier growth naturally.

👉 See How It Works >>

Here are key strategies to help reduce muscle loss during weight loss:

Resistance training—strength training or weight lifting—is one of the most effective ways to protect lean mass during dieting. It stimulates muscle protein synthesis and helps the body retain nitrogen, preserving muscle even under energy deficit. This contractile activity essentially tells your body, “This muscle is being used—don’t break it down.”

Studies show that resistance training not only preserves lean muscle mass but also increases fat loss, improving overall body composition. 

Meanwhile, relying on cardio alone during a large calorie deficit may actually accelerate muscle loss. Cardio increases energy demand without providing the mechanical stimulus needed to maintain muscle tissue.

That said, any exercise is better than none, especially during more restrictive diets. For example, one study found that as little as 45 minutes of low-intensity exercise per day—such as strolling, gardening, or easy cycling—reduced arm muscle loss by 29%, while 8 hours of low-intensity walking reduced leg muscle loss by 57% compared to limbs that did no activity. 

This shows that even gentle movement helps signal the body to preserve muscle, though it still doesn’t protect muscle as effectively as resistance training.

If you’re cutting calories, consider pairing it with even a little resistance training. A few bodyweight exercises or a short HIIT routine is enough to protect your muscles and boost fat loss.

Dieting shapes the number on the scale, but pairing it with exercise helps you lose more fat while keeping your muscles strong—setting you up for a healthier, more sustainable result.