How to Lose Fat and Gain Muscle at the Same Time

Simultaneously building muscle and losing weight—a process known as body recomposition—are the twin goals of weight training and physical conditioning. But since they are contradictory physiological processes, your body resists doing both at the same time. Instead, our bodies have evolved to increase both fat and muscle in times of plenty and to lose them both in times of scarcity when food availability is low.

While fat loss is one component, body recomposition programs are not strictly weight-loss plans. To achieve muscle maintenance or enhancement and fat loss goals, you have to have a clearly documented program and you have to apply it with precision.

What to Eat to Lose Fat and Build Muscle

Losing fat requires slightly cutting back on calories, minimizing your intake of refined carbohydrates, and reducing fat consumption; building muscle demands protein. You can't pack on muscle if you don't create an anabolic environment. In other words, you have to eat enough to maintain sufficient body weight and energy to fuel exercise.

Many people underestimate how much they eat, as shown in calorimetric scientific tests. Very low-calorie diets are not necessary or recommended by nutrition experts, but in order to lose fat, you do have to create a calorie deficit. This means burning more calories than you consume, but not so many that your body is starved of energy. 

Carbohydrates are not your enemy, but when trying to lose body fat, you should try to limit your consumption of refined carbs such as biscuits, cakes, muffins, candies, puddings, potato chips and crisps, crackers, sugary drinks, etc. Instead, opt for whole food sources such as bananas, apples, oats, or other fruits, vegetables, and whole grains.

Nutritionally, there are differences between healthy dietary fats and less healthy dietary fats. In order to lose body fat, a useful approach is to aim to get 20% and 30% of your daily calories from fat. Fat has 9 calories per gram compared to 4 calories per gram for carbohydrates and proteins. This caloric difference makes it much easier to overeat when you're consuming foods high in dietary fat.

Achieving body recomposition goals generally requires decreasing dietary fat and carbohydrate intake and increasing protein intake, so replacing some of the refined carbohydrates and less healthy fats in your diet with a modest increase in protein should help maintain or enhance your muscle mass while you're losing fat. Research shows that eating additional protein during weight loss encourages your body to hold onto more lean body mass, and in conjunction with resistance training, encourages body fat loss while also maintaining muscle mass.

Try to vary your protein sources by incorporating plant-based proteins abundant in mono- and polyunsaturated fats, such as soy and pea protein, rather than sticking solely to animal-based options, which are high in saturated fat. According to a 2018 study, swapping out saturated fats for mono- and polyunsaturated fats may have beneficial effects on body weight.

When to Eat for Body Recomposition

Your body is fuel-hungry both during and after intense exercise when your metabolism has been revved up but hasn’t been fed. This exercise-induced increase in metabolism can cause the hormone cortisol to break your muscles down into glucose.

The trick is to consume just enough carbohydrates to prevent cortisol from performing this negative task, but not so much to cause your body to slip into a positive energy balance (eating too many calories to support fat loss).

Carbohydrates are your body’s preferred source of fuel, so eating a small carbohydrate-rich snack like a piece of fruit before a workout is a good idea. Giving your body some carbs before exercise will help you avoid spending your workout hungry and will provide your body a boost of energy. Be careful not to eat too much, though, or all the moving around could cause you to feel nauseous.

After your sweat session, enjoy a light meal encompassing protein, complex carbs, and electrolytes, such as a peanut butter and jelly sandwich on whole-grain bread or a banana.

It’s best to eat lighter on rest or low-intensity workout days and ensure you’re incorporating protein throughout your waking hours. Remember to drink plenty of water before, during, and after exercising and on your rest days.

How to Exercise to Build Muscle

Only doing one type of exercise throughout the week isn’t enough to make significant changes to body composition. It’s important to vary your workouts, incorporating a mix of weight training and cardio.

To maintain muscle and bone mass while also losing body fat, your body needs stimulatory stress. That stress should be in the form of relatively intense weight lifting workouts at least three days each week—with rest days in between.

Although lifting lighter weights with higher repetitions will encourage muscle growth, you are much more likely to see results if you lift heavy or at least 65% of your maximum lift possible. For example, if you can squat a maximum of 130 pounds (60 kilograms), then you should look at training with at least 85 pounds (38 kilos). If you don't or cannot measure your maximums, then a simple rule of thumb is to make sure the final repetition in any set is hard to complete.

Aerobic exercise helps you burn off those calories. Steady-state cardio at a moderate pace, or short bursts of high-intensity cardio intervals—in conjunction with a good weight training program—will get you in a good place for fat loss. If you do cardio for longer than about an hour, however, you risk breaking down muscle for fuel.

To avoid monotony, try cycling between the two types of exercise (with rest days interspersed), or combine them in a HIIT-style workout. You'll also want to vary which muscles you work each day. Perhaps dedicate one day to lower body, another day to core, a third day to upper body, and fourth for full body.

Why Rest and Recovery Are Essential

In addition to eating healthfully and exercising, rest is equally important when aiming for a certain fitness goal. Building muscle isn’t as simple as lifting weights and eating more protein. When challenged to lift heavier weights or push through added resistance, your body breaks down muscle fibers before building them back up. This process is known as muscle hypertrophy, and it's what increases muscle size and mass.

Your body needs time off to recover and repair itself. Plan to take at least one or two days off from your workouts each week. If you feel that your body is not coping with the volume and intensity of your exercise plan, consider reducing it by half or taking a few additional days off. 

Getting enough sleep is also imperative. Research from 2019 on sleep and exercise in athletes found that there are “clear negative effects of sleep deprivation on performance,” such as less-than-optimal endurance, strength, vigor, reaction time, and accuracy.

Aim to get a consistent amount of sleep each night by going to bed and waking up at the same time, even on weekends.