People are getting fatter in every Western country and also in the developing world. The World Health Organization (WHO) recognised obesity as a ‘global epidemic’ over 20 years ago.1 In this chapter, we explore:
In 2010, the Scottish Intercollegiate Guideline defined obesity as ‘a disease process characterised by excessive body fat accumulation with multiple organ-specific consequences’.2
The medical definitions of ‘overweight’ and ‘obesity’ have been traditionally based on body mass index (BMI) results (Table 7.1). Body mass index is calculated using the following formula:
Table 7.1BMI categories for adults ||Download (.pdf) Table 7.1 BMI categories for adults
|Weight category ||BMI |
|Underweight ||<18.5 |
|Normal ||18.5–24.9 |
|Overweight ||25.0–29.9 |
|Obesity I ||30.0–34.9 |
|Obesity II ||35.0–39.9 |
|Extreme obesity III ||>40.0 |
So, if you weigh 80 kilograms and are 1.80 metres tall, your BMI is:
Body mass index levels are the most commonly used measure of obesity,3 but they have their limitations, especially in men with large muscle mass and people with non-Caucasian ancestry. A number of other ways of measuring obesity are shown in the box.
More accurate measures of body fat
Body fat percentage is more precise than BMI. There are a number of methods of calculating body fat percentage. DXA (dual-energy X-ray absorptiometry) scan
This total body scan is used more commonly to measure bone density, but also measures fat and muscle mass. It is the most accurate but also the most expensive method. Body impedance analysis devices (BIA)
Bioelectrical impedance analysis (BIA) measures the body’s resistance to a light electrical current. These are cheaper and quicker than DXA scans, but are not as accurate. Skin callipers
In skinfold testing, skin callipers are used to pinch the skin and the subcutaneous fat (fat underneath the skin), pull the skinfold away from the underlying muscle, and measure its thickness.
Skin callipers can be used at a single site or a sum of skinfolds can be performed. This is commonly used by fitness personnel working with sporting teams, and as long as the same person is doing the measuring, they are reasonably accurate at detecting changes in body fat. Bathroom scales
Old-fashioned but still a good indication of progressive weight loss (or gain). Waist measurement
Measure your waist circumference with a tape measure. Place the tape measure directly on your skin, halfway between your lowest rib and the top of your hip bone, roughly in line with your belly button. Breathe ...