SINGAPORE - From "skinny fat" to underwater weighing, The Straits Times answers some questions readers might have about body fat and how they can go about measuring it.
1. How much body fat is considered healthy?
A body fat range of 10 to 22 per cent for men and 20 to 32 per cent for women is considered satisfactory for good health, according to the American College of Sports Medicine.
2. Why do you need to know how much fat you have?
Knowing how much body fat you have can help assess your health risks, even if you are not obese.
"It is the fat, and not the weight, that leads to morbidities," said Dr Derek Koh, head of Thomson Lifestyle Centre.
A diagnosis of obesity caused by increased body fat can prompt investigations into problems such as high blood pressure or blood sugar levels, he added.
Obesity raises a person's risk of chronic diseases, including hypertension, type 2 diabetes and heart disease.
Dr Koh said studies have shown that health risks rise with an increase in body fat, especially visceral fat.
3. What is visceral fat?
Visceral fat is the fat that surrounds the liver and other abdominal organs.
It is of particular concern because it is biologically active.
According to the Harvard T.H. Chan School of Public Health, visceral fat releases fatty acids, inflammatory agents and hormones that lead to higher levels of low-density lipoprotein (LDL) or "bad" cholesterol, triglycerides, blood glucose and blood pressure.
Dr Sonali Ganguly, a consultant at the Singapore General Hospital's department of endocrinology, said: "Asians tend to accumulate more intra-abdominal (visceral) adipose tissue - the "harmful fat" that places them at a higher risk of metabolic diseases."
4. Does a person's body mass index (BMI) necessarily reflect how much fat he has?
No. While BMI has been used to classify people as overweight or obese, it does not directly assess body fat.
A muscular person could have a high BMI, but not a lot of fat.
At the same time, "skinny fat" individuals may assume they are healthy because they do not have a high BMI.
Dr Koh said: "Body fat would be the best measurement to assess health risks that come with weight, as it is the fat that relates to the risk and not the weight."
5. Can I be lean and still have a high body fat content?
Yes, a person with a normal weight can have a high percentage of fat mass and a low amount of muscle mass, which results in the term "skinny fat".
This is also known as normal weight obesity, says Dr Asim Shabbir, the director and senior consultant at the National University Hospital's Centre for Obesity Management and Surgery.
The centre has seen people with a healthy weight, but who have metabolic diseases like diabetes, hypertension and hyperlipidemiaor high cholesterol.
Dr Koh said: "I see patients with normal weight obesity daily. It is first suspected when I notice that they have a prominent waistline.
"It is confirmed when they do the BIA test. These patients have a higher risk of diabetes, hypertension and dyslipidemia. As a result of these morbidities, they also have a higher risk of heart disease."
Dr Ganguly noted that there are many people in Singapore who look lean but are "viscerally obese". This means that although they look lean, they have a high body fat content.
They are known as metabolically obese but normal weight individuals.
They are predisposed to metabolic complications despite having a normal BMI.
6. What are some myths about measuring body fat that have been debunked?
a. The thigh gap method
It claims that if you can stand with your legs together and see a gap between your thighs, you are slim. Doctors say having a "thigh gap" depends on a person's bone structure and musculature, not whether they are thin or not.
b. The belly-button challenge
Wrap one arm around your back, and if it touches your belly button, you are slim, the challenge dictates. All this tells you is how flexible your arms are.
c. The collar bone challenge
This one claims that if a person can balance a roll of quarter coins in the space in their collarbone without them falling off, the person has prominent enough collarbones and is sufficiently skinny. There is yet to be any scientific theory to support such a challenge.
7. How can you assess how much body fat you have?
a. Bioelectrical impedance analysis (BIA)
A common method is to use bioelectrical impedance analysis (BIA) to calculate body composition.
All you have to do is input your gender, height and age into the BIA machine. There are scales which look and work like a weighing scale, hand-held devices and one that incorporates both. They work by sending an imperceptible electrical current through the body - usually the hands and feet.
"This electrical signal passes quickly through water that is present in hydrated muscle tissue but meets resistance when it hits fat tissue," said Dr Koh.
"This resistance is measured and input into scientifically validated equation and algorithms to calculate body-composition measurements."
While this method is fast, easy and painless, it has its limitations.
The amount of water mass in tissues can skew the readings, so whether a person is hydrated or not affects the accuracy of the test.
Dr Cindy Ng, principal physiotherapist at Singapore General Hospital, said the variation of readings could be as much as 10 per cent of one's body fat percentage.
The amount of food eaten may also affect the readings due to the fluids present in food, she said. To get an accurate reading, fast for four to six hours before the test. During this time, you can take a few sips of water, said Dr Ng.
To minimise errors, you should avoid alcohol consumption eight hours before the test and also avoid vigorous exercise four hours prior to the test.
b. Skinfold tests
This measurement done with callipers is mainly used for research purposes as it is hard to get a good measurement.
Various body sites are measured. The four common areas are the biceps, triceps, subscapularis (bottom end of the shoulder blade) and above the hip bone.
Up to three readings are taken at a site, from which an average will be used.
It takes a while to master the skill of using a calliper. For instance, it is easy to grip some muscle with the fat, when you are supposed to grip just the fat, Dr Ng said.
The number of sites where the measurements are taken and the equation used to calculate body fat can also affect the results.
c. Underwater weighing
A person is weighed normally in a dry environment as well as when he is completely submerged in water, and the difference in the readings is used to assess the level of body fat.
Bones and muscles are denser than water, while fat tissue is more buoyant. Someone with a large amount of body fat will weigh much less underwater.
While the measurements are very accurate, this method is inconvenient and time-consuming, and thus done mainly for research, experts said.
d. Dexa scans
Dexa, which stands for dual- energy X-ray absorptiometry, reveals how much of a person's body weight is made up of fat, bone or lean tissue.
Magnetic resonance imaging (MRI) scans can also be used to measure body fat.
These tests are very accurate but expensive, and thus used in the study of diseases or clinical research, said Dr Asim Shabbir, the director of the National University Hospital's Centre for Obesity Management and Surgery.
e. Measuring waist circumference
Most studies suggest a waist circumference of over 80cm in women and over 90cm in men for Asians when it comes to the risk of developing metabolic diseases.
This is why "simple techniques like measuring the skinfold and waist circumference should not be rejected because they may appear unsophisticated", Dr Shabbir said.
People with BMI scores above 23 and a generous waistline - more than 40 inches (102cm) for men, and 35 inches (88cm) for women - are more likely to have elevated levels of body fat, said Dr Koh.
To take your measurement, place the tape measure around your middle, just above your hip bones, says the Centers for Disease Control and Prevention. The tape should be snug but not too tight. Breathe out and take the measurement.
8. What can people with a high body fat percentage do to minimise their health risks?
Dr Ganguly advises normal-BMI people with a high body fat percentage or a family history of cardio-metabolic disease to measure their waist circumference.
They should have their body fat measured and they should also go for blood tests to check for type 2 diabetes, hyperlipidemia or fatty liver, she added.
Dr Shabbir said that people with more visceral fat have a higher risk of developing metabolic diseases.
However, factors like one's environment, stress and eating behaviour can be modified easily to help alter disease processes, he added.