Chapter
2
18
Chapter 2: Understanding obesity
ISSUES: Fitness & Health
Understanding obesity
About obesity
The epidemic of obesity is now
recognised as one of the most
important public health problems
facing the world today. Tragically,
adult obesity is more common globally
than under-nutrition. According to
the World Health Organization (2014),
there are around two billion adults
overweight, of those 670 million are
considered to be affected by obesity
(BMI ≥30 kg/m²) and 98 million
severely affected by obesity (BMI ≥35
kg/m²). If current trends continue it is
estimated that 2.7 billion adults will be
overweight, over one billion affected
by obesity and 177 million adults
severely affected by obesity by 2025.
We estimate that around 224 million
school-age children are overweight,
making this generation the first
predicted to have a shorter lifespan
than their parents.
What is obesity?
Obesity is a medical condition
described as excess body weight in the
form of fat. When accumulated, this fat
can lead to severe health impairments.
What causes obesity?
Obesity is caused by an energy
imbalance; when intake of calories
exceeds expenditure of calories,
the surplus energy is stored as body
weight. There are a multitude of
‘obesogenic’ factors contributing to
the increased energy consumption
and decreased energy expenditure
that are responsible for obesity,
including:
Ö
Declining levels of physical labour
as populations move from rural
to urban settings and abandon
walking in favour of driving,
labour-saving devices in the
home, and the replacement of
active sport and play by television
and computer games.
Ö
Higher levels of food consumption,
or an increase in energy density
(particularly fat content) of the
food we eat.
Ö
Social, economic, educational
and cultural factors are important
underlying causes of obesity,
although how they inter-relate
to promote or protect against
the development of obesity is
complex and varies considerably
by country.
How is obesity measured?
The most widely-used method of
measuring and identifying obesity is
Body Mass Index (BMI) (BMI = weight
in kg/height in m
2
).
Overweight, or pre-obesity, is defined
as a BMI of 25–29.9 kg/m
2
, while a
BMI >30 kg/m
2
defines obesity. These
BMI thresholds were proposed by
WHO expert reports and reflect
the increasing health risk of excess
weight as BMI increases above an
optimal range of 21–23 kg/m
2
, the
recommended median goal for adult
Caucasian populations (WHO/NUT/
NCD, 2000).
While BMI is a simple measure that is
very useful for populations, it should
be considered a rough guide for
predicting risk in individuals. The
distribution and amount of body
fat are also crucial determinants
of some obesity-associated health
risks. Visceral fat, particularly in the
abdominal region, has a stronger
association with type 2 diabetes and
cardiovascular disease than BMI.
Accordingly, measures of central
The World Health Organization International Classification of
adult underweight, overweight and obesity according to BMI
Classification
BMI Kg/m²
Principal cut off points Additional cut off points
Underweight
<18.50
<18.50
Severe thinness
<16.00
<16.00
Moderate thinness 16.00 – 16.99
16.00 – 16.99
Mild thinness
17.00 – 18.49
17.00 – 18.49
Normal range
18.50 – 24.99
18.50 – 22.99
23.00 – 24.99
Overweight
≥25.00
≥25.00
Pre-Obesity
25.00 – 29.99
25.00 – 27.49
27.50 – 29.99
Obesity
≥30.00
≥30.00
Obesity class I
30.00 – 34-99
30.00 – 32.49
32.50 – 34.99
Obesity class II
35.00 – 39.99
35.00 – 37.49
37.50 – 39.99
Obesity class III
≥40.00
≥40.0
Source: WHO website (
)
