In this article, we explore how these shortcomings of BMI can be
outweighed by the valuable insights it provides for doctors and health
experts to be able to define and diagnose obesity objectively, and to
check and keep track of obesity rates in a country.
BMI is a simple mathematical formula using a person’s weight compared
to their height. It is calculated as your weight (in kilograms)
divided by the square of your height (in metres) or BMI = Kg/M2.
The result of this calculation is a number that can be used to
categorise individuals into different weight classifications, ranging
from underweight or normal weight to overweight and various levels of
obesity. If you want to calculate your BMI, you can use our handy
While the BMI tool has been widely adopted across the world for many
years, it’s not perfect. There have been calls to move away from the
tool due to the following criticisms:
Body composition: Muscle is denser (heavier) than fat.
However, BMI cannot differentiate between weight from fat and weight
from muscle, meaning some individuals may be wrongly categorised as
“overweight” or “obese”. Also, BMI does not consider
where a person stores their body fat. This is important,
as body fat stored in certain areas, such as the stomach region, may
carry greater health risks than other areas.
Diversity considerations: BMI doesn't take wider factors of
health outcomes such as sex, age, ethnicity, or other health
conditions into consideration. So, this
‘one-size-fits-all’ approach can’t account for certain variations,
such as how men and women store fat differently or the muscle loss
that happens as we age.
Self-reported data: Often, BMI data is self-reported, and
people can give unreliable numbers when self-reporting their height
and weight measurements, leading to incorrect calculations.
Types of obesity: BMI does not consider the recent move to
categorise different types of obesity to give individuals the most
appropriate treatment. This is discussed in more detail
in the article: 'Phenotyping obesity: when does excess weight become
Despite its downsides in certain groups of people, BMI is generally
an important and beneficial measure of a person’s level of body fat,
and it continues to be used globally for the following reasons:
Simplicity for individuals: 51% of the global population will
be living overweight or obesity within the next 12
years. As a simple and easy-to-use tool, BMI empowers
larger numbers of people to self-evaluate their health relative to
their weight, regardless of their level of medical knowledge or
access to specialist obesity support.
Simplicity for doctors: Primary care doctors play an
important role in the weight management journey of those living with
obesity, although often there is little time to perform a full
weight assessment. BMI can be an quick way to identify
those who should be referred to an obesity specialist.
Non-Invasive: BMI offers a discreet, non-invasive method to
help individuals evaluate their weight. While BMI can be
calculated by a doctor, some individuals may prefer to do it from
the comfort of their own homes if they’re concerned about feeling
judged or self-conscious about being touched in places that they
find uncomfortable or are sensitive about.
Cost-effective: Healthcare costs are soaring. With
obesity-related costs predicted to cross $4 trillion per year by
2035, BMI provides a universal, cost-effective way to
assess and monitor obesity trends across large numbers of people.
This is particularly important in a world where obesity rates and
their financial effects vary significantly between countries and how
developed they are. For example, in low-income countries,
obesity rates among adults are expected to double from 2020 to
2035. Whereas in some high-income countries, the speed at
which obesity rates rise appears to be slowing down.
BMI continues to be a valuable and cost-effective tool that is
easily accessed and used by doctors and individuals. While it has
served as a useful measure to understand obesity at a population level
for many years, it's important to remember that obesity is a complex
disease. Every individual's journey with weight is unique. The most
comprehensive way to understand and manage obesity and your individual
circumstances is to have open conversations with healthcare