Weight loss is an accomplishment, but you should be aware that you lose fat AND muscle when the pounds come off. Muscle mass is important, whether you're losing weight to be healthier or to look better. By monitoring your body fat percentage, you can gauge how much fat you're losing vs. muscle mass.
DEXA scans are the most accurate way to measure your body fat and muscle mass.
Weight Loss and Muscle Loss
You lose weight by burning more calories than you're taking in, explains an article from the National Heart, Lung and Blood Institute. You can go on a diet to eat fewer calories, exercise to burn more calories or combine diet and exercise.
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Either way, weight loss means your body isn't getting all the energy it needs, so it has to use its own fuel. Fat gives you a massive storage supply of energy. Each pound of fat in your body is equal to about 3,500 calories, according to an article from Harvard Health Publishing.
With so much energy stored as fat, it seems strange that your body would break down muscle tissue for energy as you lose weight. An article from the Gatorade Sports Science Institute explains that when you get leaner, about 70 to 80 percent of the weight lost is body fat. The other 20 to 30 percent is lean tissue.
Lean tissue can mean organs, bones, tendons and ligaments, but most of the weight lost is from muscle. Your body is constantly breaking down fat and muscle tissue. At the same time, it's making new fat and muscle. When you're in a calorie deficit, your body is breaking down both muscle and fat tissue at a faster rate, which contributes to weight loss.
Read more: Why Am I Losing Weight But Not Body Fat?
Muscle Mass Is Important
Muscles look good and make you stronger, but there's more to it than that. You need to hold onto your muscle mass as you age, advises a January 2016 review published in Biogerontology.
According to the review above, adults who hold onto more muscle mass as they age are healthier and live longer. Muscle mass naturally declines as you age, so it's important to build it up and maintain it as long as you can.
As you age and lose muscle mass, your metabolism slows down. A January 2019 study published in The Journal of Post-Acute and Long-Term Care Medicine showed that in adults, a slower metabolism was related to sarcopenia aka muscle loss. To stay healthy and maintain your metabolism, you should try to preserve as much muscle mass as possible while on a diet.
To monitor how much muscle mass versus body fat you're losing, you need some way to measure both. Your options are based on how much time, money and effort you're willing to invest.
Fat and Muscle Measurements
It's hard to gauge how much fat you've lost from your diet or workout just by looking in the mirror. Instead of relying on the physical signs of fat loss, you should seek out accurate ways to measure body fat.
Body fat calipers are small pincers that measure, in millimeters, how much fat you can pinch with your fingers in certain areas of the body. There are two versions of the test. One version tests seven different sites and the other tests three.
The three-site method is different for males and females. For females, the test measures fat in the triceps, thighs and love handles. In men, fat on the chest, thighs and belly is measured. The results are then run through a calculator, which you can find online.
A bioelectrical impedance test requires a handheld device, which is relatively inexpensive. You'll input your height, weight, gender and age into the device, and hold the handles to get your body fat measurement.
The device sends an electrical signal through your body, measuring how much is sent out and quickly it returns. Tissues like muscle and the water in your body carry the signal quickly, whereas fat and bone slow the signal down, according to an article from Doylestown Health.
Both the skinfold method and bioelectrical impedance show you how much body fat you're losing, but neither shows how much muscle mass you're losing.
To measure that, you'll need much more advanced diagnostic techniques. A DEXA scan is one of the best pieces of technology for measuring both body fat and lean body mass, and it's commonly referred to as the "gold standard."
It's used more often to determine how much bone mass you have, but it can measure how much fat vs. lean tissue you have in multiple parts of your body. The biggest drawback to a DEXA scan is that it's inconvenient and possibly expensive, especially if you want to constantly check your body fat and muscle mass.
Checking your lean body mass and body fat percentage helps you figure out how much of the weight you're losing is muscle. It's better to use measuring tools than to look for signs of losing muscle mass. The amount of weight you lose should be almost proportional to the amount of fat lost.
For example, if you weigh 150 pounds and have 20 percent body fat, you have around 30 pounds of fat. If you lose 3 pounds, your body fat percentage should drop to around 18 percent.
If you don't have the patience for all that math, monitor your body fat percentage as often as possible to make sure you're not losing too much lean mass. Chances are, you'll lose some as your body weight drops, but you can take steps to minimize it.
Read more: What Is a Good Body Fat Percentage?
Preserving Muscle While Losing Weight
Eating fewer calories is the most important change to make in your diet when you want to lose weight. Your next priority should be to increase your protein intake. When you eat higher amounts of protein every day during weight loss, you can preserve more muscle mass.
In fact, a January 2016 study published in the_ American Journal of Clinical Nutrition_ found that subjects who ate 2.4 grams of protein per kilogram of body weight preserved more muscle mass than subjects who consumed 1.2 grams per kilogram of body weight.
It's important to note that the study subjects were engaged in an intense exercise program and eating roughly 40 percent less than their daily calorie requirements. In other words, you don't need to eat as much protein as they were, but you should eat more than normal to preserve muscle mass.
When you're in a caloric deficit, you should still exercise regularly to maintain lean muscle. A May 2017 paper published in Advances in Nutrition showed that in addition to eating more protein, exercise helped preserve muscle mass during weight loss.
Researchers explain that it doesn't matter whether you do aerobic activities or resistance training — as long as you exercise while you're losing weight, you'll preserve more muscle. While it's difficult not to lose fat AND muscle in your attempt to slim down, you can use these strategies to reduce muscle breakdown and maintain your strength.
- Advances in Nutrition: "Preserving Healthy Muscle during Weight Loss"
- The American Journal of Clinical Nutrition: "Higher Compared With Lower Dietary Protein During an Energy Deficit Combined With Intense Exercise Promotes Greater Lean Mass Gain and Fat Mass Loss: A Randomized Trial"
- Journal of Investigative Medicine: "Advanced Body Composition Assessment: From Body Mass Index to Body Composition Profiling"
- Doylestown Health: "Bio-Electrical Impedance Analysis (Bia) - Body Mass Analysis"
- NCBI: "The Theory and Fundamentals of Bioimpedance Analysis in Clinical Status Monitoring and Diagnosis of Diseases"
- ACE Fitness: "Percent Body Fat Calculator: Skinfold Method"
- Journal of Post-Acute and Long-Term Care Medicine: "Decreased Basal Metabolic Rate Can Be an Objective Marker for Sarcopenia and Frailty in Older Males"
- Biogerontology: Live Strong and Prosper: "The Importance of Skeletal Muscle Strength for Healthy Ageing"
- Gatorade Sports Science Institute: "Protein and Exercise in Weight Loss: Considerations for Athletes"
- Harvard Health Publishing: "Simple Math Equals Easy Weight Loss"
- National Heart, Lung and Blood Institute: "Balance Food and Activity"