To build muscle and lose fat at the same time, most people need to eat at a slight caloric deficit: roughly 200 to 500 calories below their total daily energy expenditure. This small gap provides enough of a shortfall to burn stored fat while still supplying the raw materials, especially protein, that muscles need to grow. The exact number depends on your body weight, activity level, and how long you’ve been training.
Why a Small Deficit Works
Building muscle and losing fat seem like opposite goals. Muscle growth typically calls for extra energy, while fat loss requires a shortage of it. But your body can bridge that gap by pulling energy from fat stores to fuel the muscle-building process, as long as the deficit isn’t too aggressive. A moderate caloric shortfall supports fat loss without starving your muscles of what they need to repair and grow after training.
Cut too deep, say 800 or 1,000 calories below maintenance, and your body starts breaking down muscle tissue for fuel. That defeats the purpose. The sweet spot for most people is a deficit of about 10 to 20 percent below maintenance calories. For someone whose maintenance sits around 2,500 calories per day, that means eating roughly 2,000 to 2,250 calories.
How to Find Your Maintenance Calories
Your maintenance number is the total calories you burn in a day through basic body functions, daily movement, and exercise. You can estimate it using a formula that accounts for your age, height, weight, and activity level. The Mifflin-St. Jeor equation is widely used and tends to be reasonably accurate for people under 30 with a normal body weight. For people who are overweight or between 30 and 60, the Katch-McArdle equation, which factors in lean body mass, has shown slightly better accuracy. That said, research on healthy women found that every common estimation equation tends to overestimate how many calories you actually burn at rest, with even the best formulas only landing within 10 percent of the true value about 40 percent of the time.
The practical takeaway: treat any calculator result as a starting point, not gospel. Use it for two to three weeks, track your weight and how your clothes fit, then adjust. If you’re losing more than about a pound per week, you’re cutting too hard for recomposition. If your weight isn’t budging at all and you don’t see visual changes, trim another 100 to 200 calories.
Protein Is the Non-Negotiable Piece
Calories set the overall energy balance, but protein is what actually drives muscle growth in a deficit. Current sport nutrition guidelines recommend 1.6 to 2.4 grams of protein per kilogram of body weight per day when you’re eating below maintenance. For a 165-pound (75 kg) person, that works out to roughly 120 to 180 grams of protein daily. Cleveland Clinic suggests a similar range of 110 to 150 grams per day for someone at that weight, drawn from lean meat, fish, eggs, and Greek yogurt.
Hitting the higher end of that range matters more when your deficit is steeper or when you’re already fairly lean. The leaner you are, the harder your body fights to hold onto fat stores, and the more protein you need to signal your muscles to stick around. Spreading protein intake across three to five meals, rather than loading it all into one or two, also appears to improve how well your body uses it for muscle repair.
Your Training Experience Changes Everything
Not everyone can pull off building muscle in a deficit equally well. Your training history is the single biggest factor determining how realistic this goal is for you right now.
If you’re a beginner with less than about three months of consistent strength training, or you’re returning to the gym after a long break, your body is primed for recomposition. Untrained muscles respond dramatically to a new stimulus, and the rate of muscle gain in beginners is high enough to happen even when calories are restricted. People in this category can expect to gain noticeable muscle and strength while losing fat, sometimes for six months or longer before progress stalls.
People who carry a significant amount of excess body fat also have an advantage. Their larger fat stores provide a deep reservoir of energy that the body can tap for muscle building, making a deficit less of a threat to new muscle tissue.
If you’ve been training consistently for a year or more and you’re already at a moderate body fat level (roughly 10 to 20 percent for men, 18 to 28 percent for women), simultaneous muscle gain and fat loss becomes much slower and harder to measure. At this stage, many people find it more efficient to cycle between dedicated fat-loss phases and muscle-building phases. A common approach is to cut until you reach a body fat percentage you’re comfortable with, then eat at a slight surplus (200 to 300 calories above maintenance) to add muscle, and repeat.
Calorie Cycling: Eating More on Training Days
One strategy that bridges the gap between fat loss and muscle gain is calorie cycling. The concept is straightforward: you eat more calories and carbohydrates on days you lift weights, and fewer on rest days. On training days, you might eat at or slightly above maintenance to fuel your workout and recovery. On off days, you drop to a more noticeable deficit.
Over the course of a week, this still averages out to a mild deficit, so fat loss continues. But the extra fuel on training days gives your muscles better conditions for growth right when they need it most. A simple version looks like this for someone with a 2,400-calorie maintenance level: eat around 2,600 calories on three or four lifting days, and around 1,800 to 2,000 calories on rest days. The weekly average lands near 2,200, creating a moderate overall deficit.
Sleep Quietly Undermines the Process
Calorie and protein targets get all the attention, but sleep has a surprisingly direct effect on whether your body builds muscle or stores fat. Research from Northwestern University found that even a single night of poor sleep altered how genes function in both fat tissue and muscle tissue. Specifically, fat cells showed changes in gene regulation that mirror patterns seen in people with obesity or type 2 diabetes, while muscle tissue showed disrupted metabolic activity.
One bad night won’t ruin your progress. But when sleep loss becomes a pattern (consistently getting under six hours), it shifts your body’s metabolism in the wrong direction: favoring fat storage and impairing muscle repair. For anyone trying to recompose their body, seven to nine hours of sleep is not a luxury. It’s as fundamental as the calories themselves.
Putting the Numbers Together
Here’s a practical framework to start from, using a 170-pound (77 kg) person as an example:
- Estimate maintenance calories: Use an online calculator based on the Mifflin-St. Jeor or Katch-McArdle equation. A moderately active 170-pound person typically lands between 2,300 and 2,700 calories per day.
- Set your deficit: Subtract 10 to 20 percent. That puts your daily target around 1,900 to 2,400 calories, depending on your activity level and starting point.
- Lock in protein: Aim for 1.6 to 2.4 grams per kilogram of body weight. For 77 kg, that’s 123 to 185 grams of protein per day.
- Fill remaining calories with carbs and fat: Prioritize carbohydrates around your training sessions for energy and recovery. Keep dietary fat at roughly 20 to 30 percent of total calories to support hormone production.
- Adjust every two to three weeks: Track your weight, measurements, and strength in the gym. If strength is dropping, eat slightly more. If fat loss has stalled, trim calories by a small amount or add light cardio.
Strength training is the essential driver of this entire process. Without a consistent stimulus telling your muscles to grow, a caloric deficit will simply result in weight loss, with some of that weight coming from muscle. Three to four resistance training sessions per week, focused on progressively lifting heavier loads over time, is the baseline that makes recomposition possible.