Despite its widespread use as a way of measuring body mass, there's a lot that a scale fails to tell about a person's health. Instead of measuring weight alone, people who are making efforts to "lose weight" should ideally use a simple body fat calculator to track changes in body composition.
This is because losing fat isn't always about losing weight, and losing weight isn't always healthy. A person can still lose fat but gain weight because they gained muscle; on the other hand, that person could lose weight and be losing just as much muscle as fat.
BMI: Not Always Accurate
If you're someone who tracks your weight-loss efforts on the scale, you're not alone — it's the method that's easiest and most accessible for the everyday person. And in many cases, even doctors and experts use weight as a rough estimate of whether a person's mass is in a healthy range or whether they are at risk for disease and other complications associated with overweight and obesity.
The National Heart, Lung, and Blood Institute (NHLBI) defines a healthy weight as one that's appropriate for a person's height, and encourages people to know their body mass index (BMI). This ratio of a person's weight to height is determined by dividing weight in kilograms by height in meters squared.
Having trouble with the math in determining your BMI? Don’t worry. The NHLBI offers a tool where you can plug in your weight in pounds and your height in feet/inches, and it does the math for you.
A healthy body mass index is one between 18.5 and 24.9, according to the NHLBI. A person who has a body mass index of 25 or greater would be considered to have overweight, and a person with a body mass index of 30 or greater would be considered to have obesity. These high BMIs suggest that a person is at a greater risk of heart disease, high blood pressure, Type 2 diabetes, gallstones, osteoarthritis, sleep apnea and certain cancers.
But relying exclusively on weight — and on BMI — assumes that any extra weight a person is carrying above their "normal" number is all fat when it potentially could be muscle. Therefore, as the NHLBI points out, an especially muscular person could have a high BMI but a moderate or low body fat percentage.
For this reason, BMI is unreliable when it's looking at people who have higher-than-average muscle mass (such as athletes) or lower-than-average muscle mass (such as the elderly).
Understanding Body Composition
Instead of looking simply at weight, a person should consider their overall body composition, meaning how their fat mass (the amount of fat they have on their body) measures up against their lean mass.
The University of Utah explains that it's more important for a person to be fit than it is for them to be skinny or weigh very little, and being at a low weight doesn't necessarily mean that a person has a low body fat percentage. It's also important to remember that if you lose weight, you are at risk of losing muscle mass as well.
Knowing and tracking your body fat percentage will give you an idea of how much fat you have compared to lean mass, and if you are on a weight-loss or weight-gain journey, how much of your weight change is fat and how much is muscle.
Remember, all individuals need some amount of body fat, and having too little body fat can pose problems just as having too much can. AARP points out that you need body fat for stored energy, absorbing fat-soluble vitamins, retaining body temperature and providing protection for the body against trauma. More people struggle with having too much body fat than having too little, but that doesn't mean people should be trying to lose all of their body fat.
A healthy body composition, on the other hand, means less risk of cardiovascular disease, diabetes, metabolic disease and osteoporosis, explains the University of Utah. It will also improve your ability to perform daily activities, increase your energy, decrease your stress and help you maintain your cognitive function.
A Simple Body Fat Calculator
One of the easiest ways to determine your ratio of lean mass to fat mass is with the use of calipers to measure your skinfold at designated spots around your body. The American Council on Exercise (ACE) offers instructions on how to measure skinfolds:
- Determine which parts of the body you'll measure. ACE recommends measuring the thigh, chest and abdominals, all from the right side of the body.
- Using your thumb and index finger with your left hand, pinch and hold the skinfold.
- Take the calipers and place them perpendicular to the site with their pads around the skinfold about a quarter-inch away from your fingers.
- Release the trigger and wait one or two seconds before reading the dial. Round to the nearest 0.5 millimeter if necessary.
- You should take two measurements at each site, waiting at least 15 seconds to allow the fat to return to its normal thickness.
- If necessary, continue to take measurements until you have two that vary by less than 1 millimeter in each bodily location. This will ensure you're getting the most accurate measurement.
Once you have taken skinfold measurements on the thigh, chest and abs, you can plug the numbers into ACE's simple body fat calculator on its website, along with your age, weight and gender. This will give you your body fat percentage, as well as your estimated lean mass and your estimated fat mass.
Note that this is not a muscle mass calculator — your lean mass includes not only your muscle but also your bones and other organs. However, if your estimated lean mass increases, it's a good sign that you are gaining muscle.
Fat Loss vs. Muscle Gain
You'd be hard-pressed to find a muscle-to-fat ratio chart, but you can look at what your percentage of body fat suggests about your overall health. Being at a higher weight does not necessarily put you in an at-risk category as long as your body fat is low and your lean mass is high.
According to the University of Utah, women are in an at-risk category if their body fat is below 15 percent (too low) or more than 40 percent (too high). Men are in an at-risk category if their body fat is less than 5 percent (too low) or more than 30 percent (too high).
Women are considered very lean between 15 and 18 percent, lean between 19 and 22 percent, moderate between 23 and 30 percent, and carrying excess fat between 31 and 40 percent. Men are considered very lean between 5 and 8 percent, lean between 9 and 12 percent, moderate between 13 and 20 percent, and carrying excess fat between 21 and 30 percent.
But how do these percentages have a bearing on your fitness efforts? Let's say you're a 170-pound male with 15 percent body fat, which puts you in the moderate range. That means you have 25.5 pounds of fat on your body and 144.5 pounds of lean mass. If you gain 10 pounds, putting you now at 180 pounds, but your body fat percentage remains 15 percent, then you have gained both muscle and fat. You now have 27 pounds of fat and 153 pounds of lean mass.
However, if you gain 10 pounds and your body fat percentage goes down, then you now have more muscle and less fat. Let's say you are now 180 pounds but with 12 percent body fat; then that means you now have 21.6 pounds of fat and 158.4 pounds of lean mass.
Then there's one final scenario to consider: You might build muscle but not gain or lose any fat. You still have the 25.5 pounds of body fat that you had when you started. But you've gained 10 pounds of muscle and are now 180 pounds. That means your body fat percentage has gone down to about 14 percent. Your muscle-to-fat ratio has still changed even though you haven't lost any fat.
Read more: 8 Healthy Ways to Burn Body Fat — and Keep It Off
Changing Your Body Composition
If you want to change your muscle-to-fat ratio, don't think it's impossible to build muscle and lose fat at the same time. However, it can be tricky. According to Columbia University, the process of building muscle, known as anabolism, requires a consistent intake of calories plus resistance exercise and adequate rest. If a person is restricting their caloric intake, then they won't have the calories they need for muscle repair.
Columbia University explains that it can be easier for an out-of-shape person with a lot of body fat to build muscle and lose fat at the same time than it is for an in-shape person to do the same thing. If you're on a weight-loss plan, you should aim to preserve your muscle mass by doing resistance training and cardio so that you maintain your strength, muscle tone and bone health.
According to a January 2018 study published in the International Journal of Sport Nutrition and Exercise Metabolism, resistance training, even without restricted dieting, may be the key to gaining muscle and losing fat. The study examined 40 premenopausal female volunteers and divided them into groups that would do either resistance training, dieting or a combination of both.
Although all groups lost fat and the group that combined resistance training and dieting lost the most fat, the group that did resistance training without dieting was the only group that gained lean mass.
Don't underestimate the importance of combined healthy eating and physical activity — you shouldn't rely on just one or the other.
The Academy of Nutrition and Dietetics notes that doing regular resistance training is the key to keeping muscle and that all individuals should be doing strength training twice a week to work all major muscle groups, including their legs, hips, back, chest, abdomen, shoulders and arms. These strength-training exercises could include resistance bands, push-ups, pull-ups and sit-ups.
As far as good nutrition goes, the Academy of Nutrition and Dietetics encourages people looking to build or maintain muscle to get 10 to 35 percent of their calories from protein, about 50 percent from carbohydrates and about 20 to 35 percent from fat.
Read more: Your Ultimate Guide to Gaining Lean Muscle
- International Journal of Sport Nutrition and Exercise Metabolism: “Resistance Training Combined With Diet Decreases Body Fat While Preserving Lean Mass Independent of Resting Metabolic Rate: A Randomized Trial”
- Columbia University: “Losing Fat and Building Muscle Mass: Can This Be Done Simultaneously?”
- University of Utah: “Want to Lose Weight? Pay Attention to Body Composition”
- American Council on Exercise: “Percent Body Fat Calculator: Skinfold Method”
- National Heart, Lung, and Blood Institute: “BMI Tools”
- Academy of Nutrition and Dietetics: “4 Keys to Strength Building and Muscle Mass”
- AARP: “The Health Benefits of Fat”
- National Heart, Lung, and Blood Institute: "Calculate Your Body Mass Index"