Just knowing what you weigh is not enough. We recently posted an article about Wi-Fi Smart scales that included a few models that measure body composition. So we thought it would be good to give you more information about these metrics. Body composition – what you actually consist of is an important indicator of your true health status. Weighing yourself daily and tracking it is a smart and healthy thing to do. But simply knowing your weight is not always going to tell how healthy you are. As you will learn later in this article you can be be very thin and still be fat.

Normal male body composition

Body composition analysis is not a new thing. It started in the 19th century when biochemist Justus Von Lebig purported that our bodies are composed of substances similar to that which we eat. Then scientists differentiated between fat and other substances. They discovered that it has very low water content relative to other non-solid mass within you. This science has evolved and technology has allowed it to become very exact. It might seem to those of us who are overweight that we are all fat. As you may already know, we are mostly composed of water. On average water is 72% of your Fat Free Mass, protein is 21% and bone is 7%.

Lean Man
154 lb.
Obese man
220 lb.

As you can see, the distribution of water, protein and fat compared to other components is different for an obese person. The ratio of water and protein are reduced in comparison to fat.

Autopsy is the only true  way to measure body composition and we have been having some problems getting volunteers for that weight loss program. But technology has improved so that you can get very accurate readings on key parameters. Now the common bathroom or doctor’s scale can easily be replaced by a body composition monitor such as those made by Tanita, Fitbit and Withings.

Body fat percent – the percent of your total weight that is fat

You must have some fat or you will die. So don’t go too crazy dieting. A Woman’s body must contain at least 12% fat in order to be healthy. Men must have at least 5%. You’ve got to have it to be healthy. Fat provides energy.  If you are short of it, you will know it by being tired – all the time. Fat has a role in regulating hormones. It is the cushion between organs without which they can become damaged. Woman are particularly vulnerable to health problems related to low fat including low energy, eating disorders, irregular menstruation (or lack thereof) and decreased bone mass (osteoporosis). Just like people, there are essential fats and nonessential ones (just kidding – all people are important).

Lipids include essential fat. Lipids molecules contain hydrocarbons that merely are the foundation of the structure and function of living cells. Kidding aside – fat can be very essential.

It’s that nonessential stuff that we all hate and are warring against. It accumulates as we have said around your organs, below your skin and in fat cells (that makes sense). You get an accumulation of this fat by eating more calories than you burn. Too much of this kind of fat not only can make you look bad – it will kill you. That is because it is not metabolically active. It is not alive in the way your muscle, bone, and organs are. They regenerate while fat is an accumulation that can permeate healthy organs and cause disease. All through this website are articles about it causing heart disease, diabetes, cancer and liver disease. Keeping your BMI below 24 may be the best thing a healthy person can do to stay that way. But BMI only tells you how fat you are for your height. It says nothing about how much of it makes up your composition – your body fat percentage. If you have no muscles, you can be very thin and still be fat and unhealthy. So you need to know how much of you is composed of fat relative to bones, muscle and organs (and everything else). You need to know your body fat percentage. High levels that can cause serious health catastrophes are 32 percent and over for women – 25 percent and over for men. Women have an average body fat of 22 to 25 percent – men 15 to 18  percent. Women should shoot at having a body fat of 14 percent – men 8 percent. No additional health benefits have been found to occur below these percentages for women and men.

Some smart scales can measure visceral fat. Visceral fat is around your abdomin and is the most dangerous nonessential fat. Abdominal fat is the greatest predictor of heart disease and diabetes. The problem with visceral fat is that it is hard to lose. Diet alone is not enough. Typically, you must do extensive aerobic exercise to burn it from your midsection.

Lean Body Mass – what you have left after you lose weight and exercise

Lean Body Mass = muscle + bones + organs + skin + blood. It’s a catch all for everything besides fat. It’s all the good things you want to be made of. It can be created and made healthier by eating good foods and exercising. It can be measured by Dual Energy X-ray Absorptiometry and Bioelectrical impedance analysis(see above). The formula to compute it is:

Your Weight – (Your Weight x Body Fat %)


A cheap smart scale computes Lean Body Mass % simply by subtracting Body Fat % from 100. For younger people that’s all you really need to know. The higher your percentage of lean mass, the healthier you are. Older people may want to know more about things like bone mass. The things that deplete as you age.

Components of Lean Body Mass %:

Muscle Mass Percentage. Wikipedia says that the average women is made up of 36 percent skeletal muscle and the average male 42 percent. But there is also “smooth muscle” to consider as well as “cardiac muscle.” Smooth muscles are the involuntary muscles in the walls of  the the stomach, esophagus, intestines, bronchi, blood vessels, uterus, bladder, urethra, and the arrector pili in the skin (they control the erection of hair). Wonder how much of that a smart scale can measure? It would have to be very smart. It’s hard to find committed statistics on what an average Muscle Mass Percentage really is. In any case, it seems that within reason, the more muscle you have, the better. Muscle weighs more than fat. You can exercise and develop muscle mass resulting in weight gain while losing inches at your waist, buttocks. legs and arms (and head if you are a fathead). Weight gain is not always a bad thing.

Bone Density vs. Bone Mass %  – Bone density becomes an issue as you age. Your doctor will typically measure bone density using a specialized X-ray (DXA (Dual-energy X-ray Absorptiometry))  that sees calcium and bone minerals. Specific bones in the forearm, spine and hip are measured. As you age, bone density decreases and your bones are more breakable. We have all known older people who have taken a small fall and broken their hip. When you see children playing, frequently they fall full force and get up as though nothing happened. That same fall will break the hip of an older person with diminished bone density. So it is important to know when your bone density starts to decline and get treatment and change your lifestyle accordingly. When you lose bone density, you might lose weight as bone is the densest component of the body. Osteoporosis is a disease of the bones where they become porous causing a bone density reduction. Smart scales tell you what percentage of your mass is composed of bone. It is not an accurate measurement of bone density. But you can use a smart scale to warn you when you might be losing bone density – if your bone mass percentage starts to decline.

Body Water Percentage – water weighs more than fat. Most of your weight for the typical person is water and your water percentage fluctuates far more radically than any other component of your body. Being weight loss experts, we have witnessed large weight gains in people that were nothing more than retained water. When facing an unexpected ten pound weight gain, you always have to ask yourself, “Is this just retained water?” Water retention is not a good sign as far as your health goes, and the condition may have to be medically treated. Body Water % measurement is one of the best features you can get on a smart scale because you can know if you really gained fat or retained water. Children and babies typically are composed of 77% water. Grown women are 50% and men are 60%. Elderly people are typically 45% water. Overweight people have lower Body Water Percentage than average. Your doctor may have your water measured by sending you to a test specialist who will inject isotopes into you. (An isotope is an easily identified atom that differs from normal in the number of neutrons it has.) Then they measure for the percentage of the isotope in a blood sample. A much easier technology to use for body water percentage measurement is bioelectrical impedance analysis. That’s the technology used in a smart scale (and it can also be done medically as we explained earlier).

Weight loss surgery patients need to worry about fat even after they get skinny

That’s the most important thing we learned about body composition. You can be skin on bones skinny yet still be fat and unhealthy. So just becoming skinny is not enough. It’s a matter of what you’re composed of. You have to have muscle on your bones and that can only be built up through a balanced diet and exercise. It’s all about your lean body mass.  The more muscle you have, the healthier you will be.

“Body composition.” Body composition (pdf). Rowett research institute. Web. 19 Dec 2012.