If You're Gaining Weight, Experts Explain How to Tell If It's Muscle or Fat

Registered dietitian, exercise physiologist, and NASM-certified personal trainer Gabbi Berkow, MA, CDN, told POPSUGAR that gaining fat on your body results from eating more calories than you burn. So, anything eaten in excess whether that's protein, carbs, or fat, can be stored as fat if the calories you eat are greater than the calories you burn. Rondel King, MS, CSCS, exercise physiologist at the NYU Langone Sports Performance Centre in New York, further explained: "Let's say, for instance, you're eating an excess of 1,000 calories than your resting metabolic rate is calling for. That needs to go somewhere. What the body does as a defence mechanism, it stores those excess calories as fat."

Gaining muscle is a lot harder and requires a lot more work, Gabbi noted. "You have to progressively overload your muscles by lifting weights and continually challenging yourself over time," she said. "After every workout your muscles build more fibres so that they're better equipped to handle the stress of the next workout." But, you eventually get used to the load, which is why you have to keep increasing the intensity.

It's also about what you eat. Rondel explained that protein is necessary because it's essentially the building blocks to develop more muscle mass so you can become stronger and withstand the stresses that you've placed on your body. Since muscle is made of protein, Gabbi said, you have to consume plenty of protein, around one gram per pound of bodyweight every day, for your body to be able to build muscle. (Eating more protein will also boost your metabolism.)

Since building more muscle fibres uses up a lot of calories, you'll build the most muscle if you eat more calories than you burn, Gabbi said, so you can gain fat while building muscle. Building muscle without gaining fat, what she called a "clean bulk" where you put on muscle without eating more than your burn, is possible, but it requires "strict attention to calories and protein, and you won't put on as much muscle as you would if you ate more calories than you burned." Additionally, she said you can't significantly bulk up while you're focused on losing weight (aka, fat) due to the amount of calories required to build muscle. She discusses why muscle is important for weight loss, though, ahead.

A kilogram of muscle weighs the same as a kilogram of fat (a kilogram is a kilogram!). Muscle, though, is denser than fat, Gabbi said. "It has more water, protein, carbohydrates, and fats in it than fat does, but it takes up less space. Since density equals weight divided by volume, the same amount or weight of muscle takes up less space than fat." That's why gaining muscle is often associated with losing inches but not necessarily total scale weight, she explained (which we'll get to more later).

Measuring your body composition — how much of you is made up of water, muscle, and fat — is the best way to assess whether you're gaining fat and/or muscle, Gabbi said. Body composition can be measured most easily with a Bioelectrical Impedance Analysis (BIA), "where harmless electrical currents through your body are used." You even get a BIA scale that you step on or hold in your hands, but Gabbi said to make sure you use it on an empty stomach and when you are hydrated "since being dehydrated can erroneously send up your body fat percentage reading." Rondel noted that many gyms do a body composition test of some sort before people start programs in order to get baseline values and therefore set realistic goals.

Other tests include skinfold calipers, or "pinch tests," and they can be used to measure gains or losses in body fat. A DEXA scan — dual-energy X-ray absorptiometry — which is a radiological scan used to measure bone density, is the most accurate way to measure your body composition, but is often less accessible than a BIA scale, Gabbi said.

A CT scan and blood tests will indicate whether you've developed an increasing amount of visceral fat, and you or a doctor can take measurements of your waist circumference, since most often excess visceral fat can cause protrusion of the abdomen. You can read more about that here.

Aesthetically, it should be pretty easy to tell if you're generally gaining muscle or fat. When you gain muscle, you'll notice that they'll look more defined and are more visible, Gabbi said. (In terms of seeing your abs specifically, you'd have to also lose fat for that.) Your muscles would also be larger in size or feel "harder." If you gain fat, you'll notice more softness or "flabbiness," she said, "and you'll gain inches."

"Building muscle is what keeps your metabolism up and helps prevent weight regain, so it's absolutely key for weight loss," Gabbi told POPSUGAR, further explaining that muscle burns more calories than fat, so the more muscle you have, the more calories you'll burn at rest. Dieting and not focusing on muscle may make you regain the weight once you begin to eat more since your metabolic rate will have slowed.

Preserving your muscle mass is also important if your goal is to lose weight because when you're in a caloric deficit — which is essential for weight loss — "your body senses that it's getting less fuel, and it slows down the number of calories it burns," Gabbi said. This slows down your metabolism in order to conserve energy. Strength training and eating enough protein daily are key to keep your metabolism up so you can therefore lose weight, Gabbi said. As she mentioned before, you can't build a huge amount of muscle while trying to lose weight since you need those extra calories, but you can still get toned.

Even if you're losing fat, the numbers on the scale may not be going down if your muscle is increasing, Gabbi said. "It's essential to measure your body composition, not just total weight, when you're losing weight. You want to make sure that muscle stays the same or goes up while fat goes down," she specified. Visually, you'll see a reduction in fat, Rondel noted, and on the other hand you'll be developing muscle too, which is more dense, so you "won't necessarily see a huge change on the scale." Want proof? These women didn't lose a single kilogram, but their bodies transformed with more lean muscle and less fat. Using those numbers as a means to measure progress no matter what your goals are — whether you want to gain weight or lose weight — is important, Gabbi added.

If you're frustrated with your weight staying the same for a period of time, Gabbi noted that weight-loss plateaus often occur after losing about 10 percent of your body weight. "Your body senses that you're eating less and slows down its metabolism so you burn less calories." Here are ways to combat a weight-loss plateau. And, if your journey to bulk up has plateaued, you need to eat more, change your workouts, or kick up the intensity. Read more about that here.

Everyone has different goals, so please speak to your doctor (and/or professionals such as registered dietitians and certified personal trainers) for the right plan for you. Gabbi concluded, "Gaining muscle is hard and takes work. You have to lift heavy, eat a lot of protein, and find the balance of lifting enough while allowing for adequate recovery. Gaining fat is easy. Our bodies evolved to store excess calories as energy easily for times when food was scarce." Staying toned and losing fat is possible, but you can't bulk up and lose a significant amount of fat at the same time. "It's often best to focus on building muscle or losing fat," she said. Below, check out some places to start:

• Weekly Workout Plan to Build Muscle
• Another Weekly Workout Plan to Build Muscle
• Simple Meal Plan For Weight Loss
• Low-Carb Meal Plan For Weight Loss
• Dietitian Tips For What to Eat to Gain Muscle