Adipose tissue, more commonly called body fat, is essential for our bodies to function. While some body fat is necessary, having too much body fat poses serious health risks. Carrying excessive weight (fat) increases the risk of diabetes, heart disease, some types of cancer, and premature death.
As rates of obesity rise in North America, more focus has been put on determining what constitutes a healthy body fat level. Taking measurements is especially valuable when embarking on a weight loss journey to show change and keep motivated. Whether you want to determine if you have a healthy amount of fat, or are simply curious as to how you compare with the norms, knowing what the numbers show is important.
Body Mass Index (BMI), a ratio of weight to height, is the most common method of estimating healthy body weight. To calculate BMI, divide weight in kilograms by height in meters squared. For example, if you are 165cm (1.65m) tall and weigh 67 kg, your BMI is 24.6 m/kg2.
An ideal BMI is 18.5-24.9 m/kg2. A BMI less than 18.5 m/kg2 may pose health risks associated with having too little body fat. 25-29.9 m/kg2 is considered overweight, and more than 30 m/kg2 is considered obese.
BMI gives a general idea of what a moderately active person should weigh based on height, and is simple to calculate. However, BMI has some limitations. BMI relies on the weigh scale, which does not tell the whole story. For example, a competitive hockey player who is five foot ten and two hundred twenty pounds of pure muscle would be classified as obese. In other words, BMI does not differentiate between muscle mass and fat.
Waist girth and other measurements, such as the circumference of your chest, arms, hips and thighs can also determine body composition. Women should aim for a waist girth (around the navel) of 66-85cm, while men can aim for 82-90cm.
It is easy enough to measure the circumference of your waist, chest, or hips. As you increase your exercise level and decrease your food intake, you will ‘lose inches’. The changing measurements reflect fat loss – even if the scale reads the same. Your weight may not change if you are building muscle.
Finally, percent body fat, simply the percent of body fat your body contains, can be estimated, most commonly by measuring skin folds or with a Bioelectrical Impedance Analysis (BIA). During the skin fold test, calipers pinch and measure the fat underneath the skin at several test sites, usually the arms, back and abdomen. The sum of the skin folds is used to estimate percent body fat. A BIA machine looks like a fancy weigh scale. A small electrical signal is passed through the body, carried by water. Body fat percentage is calculated based on the principle that muscle contains more water than fat, and will carry the electrical signal.
Ideally, women should be between 14 and 24% body fat. Men should be between 6 and 17%. Measuring percent body fat distinguishes between fat and muscle- something the scale does not do. Two people can weigh the same, but differ in percent body fat. On the down side, percent body fat is often not reliable. For example, skin fold testing relies on the tester’s skill, and assumes that every person’s fat is distributed the same way. BIA readings are affected by eating, being dehydrated or exercising.
For health reasons, it is important to achieve and maintain a healthy body weight. BMI, waist girth circumference and percent body fat tests can all determine body composition. For the average person, all of the tests can generalize whether or not you carry a healthy amount of body fat. Do not become fixated on the accuracy of any of the numbers. Instead, focus on how the numbers change, or stay the same, as you incorporate exercise and healthy eating into your lifestyle.
Tanja Shaw is a Kinesiologist and Fitness Coach, specializing in weight loss, group fitness, pre and postnatal fitness, and health and wellness programs. She owns Ascend Fitness Coaching, home to Ascend Fitness Boot Camp, Stroller Boot Camp, and personal training programs. For more fitness tips go to www.ascendfitnesscoaching.com.