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Does Your BMI Really Matter? Is It Useful Or Useless? | Nutritionist Explains... | Myprotein
Jan 30, 2025
What is Body Mass Index or BMI? How is it used and is it useful? Our expert nutritionist explains everything you need to know.
BMI is one of the most common ways of grouping people by their bodyweights. In this video, Richie - our Nutrition expert, is here to explain what Body Mass Index is, how it’s used, if it’s a good measure, and if there are any alternatives.
Find Richie on Instagram: @be_more_nutrition
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Chapters:
00:00 Intro into Body Mass Index
00:45 What is BMI?
01:45 BMI categories
04:08 BMI is easy to measure
04:57 The problems with categorising people via BMI
07:43 Alternatives to BMI
10:12 Got any more BMI questions?
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0:00
body mass index is it useful or useless
0:03
let's talk about that
0:06
how's it going guys my name is richie
0:08
kirwan and today we're going to talk all
0:09
about one of the most common ways of
0:12
grouping people by their body weights
0:14
the body mass index or bmi what it is
0:17
how it's used if it's a good measure and
0:20
what are some of the alternatives bmi
0:22
has a lot of haters and if you're one of
0:23
them i'd love it if you watched all the
0:25
way to the end of this video for two
0:27
reasons so you can really understand the
0:28
problems with bmi and so you can
0:30
understand why it's still used so much
0:33
and when it can actually be useful i
0:35
just want to point out that i'm not
0:36
trying to recommend or advise against
0:39
using bmi i'm just going to talk about
0:41
the science surrounding it so you have a
0:43
better understanding yourself let's get
0:44
started so what is bmi exactly bmi was
0:47
first developed in the mid-1800s by a
0:50
polymath that's someone with expertise
0:52
in a lot of different fields of sciences
0:54
called adolf quetlet who also founded
0:57
the science of anthropometry which is
0:59
how we measure human physical shape and
1:00
sizes it was actually originally called
1:03
the questless index but became commonly
1:05
known as the body mass index in the
1:06
1970s thanks to its use by one of the
1:08
most famous nutrition researchers at the
1:10
time
1:11
ansel keys bmi is a way of measuring
1:14
someone's body weight in relation to
1:16
their height and you can calculate it
1:18
yourself by dividing your weight in
1:20
kilograms by your height in meters
1:22
squared so for someone who weighs 75
1:25
kilograms and is 178 centimeters tall
1:27
the formula looks like 75 divided by
1:30
1.78 squared and that gives us a bmi of
1:33
23.7
1:35
now bmi on its own doesn't tell us much
1:37
so scientists have created bmi
1:39
categories to group people according to
1:41
how far their weight is from the norm
1:44
for their height the world's health
1:45
organization has designated the normal
1:48
bmi range to be from 18.5 to 24.9 below
1:52
18.5 is considered underweight and with
1:54
below 16 being considered severe
1:56
underweight and actually does happen in
1:59
some extreme cases such as starvation
2:01
and even in anorexia on the other end of
2:04
the spectrum a bmi of 25 to 29.9 is
2:06
considered overweight and 30 or over is
2:09
classified as obese in fact there are
2:11
obesity classifications class 1 which is
2:13
a bmi of 30 to 34.9 obesity class 2
2:17
which is 35 to 39.9 and obesity class 3
2:21
which is a bmi of 40 or more this is
2:24
actually a problem with the name of bmi
2:26
classifications and not bmi itself
2:28
nobody wants to get their bmi measured
2:30
and to be called overweight or obese so
2:32
maybe changing the name of the
2:33
categories to something neutral like
2:35
numbers might be less unpleasant for
2:37
example a normal boi could be called
2:39
class zero and underweight could be
2:41
called bmi class minus one
2:44
or overweight could be called bmi class
2:46
plus one but the naming system probably
2:47
isn't going to change anytime soon at
2:49
this point it's really important to
2:51
point out that these categories are all
2:52
just medical terms that are used to
2:54
categorize people by weight in relation
2:57
to height science loves categorizing
2:59
things because that helps us to
3:01
understand concepts better we're also
3:02
able to observe certain health trends in
3:04
relation to different bmi categories you
3:07
see the further someone's bmi is from
3:08
the normal range in either direction
3:11
over or underweight the greater risk
3:14
they have of health problems this is
3:16
where bmi can actually have some use it
3:19
can and i say can because it definitely
3:21
doesn't apply in all cases be a really
3:23
quick and easy screening tool in
3:26
medicine for identifying when someone is
3:28
in a weight category that might put them
3:30
at a risk of a specific health problem
3:33
for example diabetes i use the word risk
3:35
here because in science we can only talk
3:37
about risk because nothing is definite
3:39
for example smoking can greatly increase
3:41
someone's risk of lung cancer it doesn't
3:43
mean they will definitely get lung
3:44
cancer if they smoke and it doesn't mean
3:46
that someone that doesn't smoke won't
3:48
get lung cancer it just means that a
3:50
smoker has a greater chance of getting
3:52
lung cancer than a non-smoker in the
3:54
same way people whose bmis are further
3:57
from the norm have a greater statistical
3:59
chance of health issues but it is by no
4:02
means definite in all cases there are
4:04
always exceptions bmi is very widely
4:08
used because it is super easy to measure
4:10
as you just need someone's height and
4:11
weight you don't need any fancy
4:13
equipment to measure those and they're
4:15
quick and cheap to work out in most
4:17
medical practices that are struggling to
4:18
get through a lot of patients in a day
4:20
this makes it really popular index to
4:23
categorize people bmi is quick cheap
4:25
easy and in a very general sense it has
4:28
a relation with some health conditions
4:31
or risk of those conditions here's the
4:33
thing though
4:34
bmi is not a way of diagnosing how much
4:38
body fat someone has nor is it a good
4:41
way of categorizing someone as healthy
4:43
or unhealthy this because bmi doesn't
4:46
tell us anything about someone's level
4:48
of body fat their body fat distribution
4:51
which is where they store body fat on
4:52
their body which is a major impact on
4:54
health or their muscle mass let me
4:56
explain why this is a major problem in
4:59
the normal bmi category you will have
5:01
people with normal levels of muscle and
5:04
body fat but you can also have people
5:06
who have very low levels of muscle and
5:08
high levels of body fat this is
5:09
sometimes known as skinny fat in popular
5:12
culture but in research we call it
5:14
sarcopenic obesity from sarcopenia which
5:16
means low levels of muscle mass and
5:18
obesity which means higher levels of
5:20
body fat we know this is actually a very
5:22
unhealthy type of body composition but
5:24
because it's in the normal bmi category
5:27
it often gets missed and overlooked on
5:29
the other hand you can find many
5:31
athletes that have high levels of muscle
5:33
and low levels of body fat but because
5:36
of all their muscle and how heavy muscle
5:38
is they are all categorized as
5:40
overweight or some as even obese so if
5:42
you just look at their bmi you'd think
5:44
that they might be at a higher risk of
5:45
health problems when in fact they may be
5:47
exceptionally healthy as many athletes
5:50
are that said a lot of people who work
5:52
out like to brag that they have a high
5:53
bmi but it's because of all their muscle
5:55
even though they might have a lot of
5:56
body fat too there comes a point where
5:58
lots of muscle isn't going to protect
6:00
someone against the negative effects of
6:02
excess body fat now with that said just
6:05
because someone has a higher level of
6:06
body fat doesn't necessarily mean
6:09
they're less healthy there are people
6:11
who have something known as
6:12
metabolically healthy obesity which
6:13
means their bmi is in the obese category
6:16
they have high levels of body fat but
6:18
they don't have any of the metabolic
6:20
issues associated with obesity like high
6:22
blood sugar insulin resistance high ldl
6:25
or bad cholesterol and low hdl which is
6:27
the good cholesterol that said people
6:29
with metabolically healthy obesity
6:32
aren't very common and are at a higher
6:33
risk of developing health issues in the
6:35
future but that's a complicated topic
6:37
that might deserve a video of its own
6:39
here's another problem with bmi
6:41
weight stigma weight stigma is when
6:43
people are discriminated against either
6:44
by thoughts or actions because of their
6:46
weight categorizing people based
6:48
exclusively on their weight or level of
6:50
body fat or bmi can lead to weight
6:52
stigma and here's an example of how if
6:55
someone who is classified as overweight
6:57
or obese goes to the doctor with a
6:59
health complaint there are some doctors
7:01
that might put their health issue down
7:03
to their body weight and tell them that
7:05
they just need to lose weight to feel
7:07
better without much further
7:08
investigation or testing not only is
7:10
that a
7:11
way to treat a patient and give advice
7:14
it also runs the risk that they miss out
7:16
on the real reason for the person's
7:18
health issue because the doctor doesn't
7:19
look beyond body weight and if that's
7:21
not bad enough
7:22
it might even stop someone in a larger
7:25
body from going to the doctor in the
7:26
future because they know they're going
7:28
to be discriminated against because of
7:29
their size and that means they might
7:32
miss out on getting the medical care
7:33
that they need so hopefully now you
7:36
understand that bmi on its own isn't
7:38
particularly useful for determining if
7:39
someone is healthy or not
7:41
what could we use instead well one easy
7:44
measure to add to bmi is someone's waist
7:46
to hip ratio or waist to height ratio
7:49
this gives us a better idea of where or
7:51
how people are storing body fat this is
7:53
because if someone is storing a lot of
7:54
body fat around their waist something
7:56
known as abdominal obesity they have a
7:59
much higher risk of suffering from
8:01
cardiometabolic diseases like heart
8:03
disease diabetes and non-alcoholic fatty
8:05
liver disease then you have something
8:07
like dexa dexa stands for dual energy
8:09
x-ray absorptiometry and it's a
8:11
technique that uses x-rays to measure
8:13
body composition gives really accurate
8:15
measurements of someone's muscle mass
8:16
body fat percentage and even where
8:18
people store body fat for example around
8:20
their abdomen or even around their
8:21
organs which is known as visceral fat
8:23
and can have a lot of negative health
8:25
effects oil dexa may be one of the best
8:28
ways to work out someone's level of body
8:29
fat and muscle it's also expensive and
8:32
can only be done in places with a very
8:34
expensive dex scanner like big hospitals
8:36
or universities and that brings us back
8:38
to why bmi is so popular it's quick
8:41
cheap and very easy to measure and
8:43
that's why it's used so much as an
8:45
initial screening tool and while bmi may
8:48
not give us much useful information on
8:50
an individual's health it is really
8:52
useful for looking at trends in
8:53
population app to give you an idea of
8:55
what i mean by this the average bmi in
8:57
places like europe and the us has been
9:00
going up pretty steadily since the 1970s
9:02
and so has the average waste
9:04
circumference you can't really say that
9:06
it's because most people are getting
9:07
jacked and putting on more muscle so
9:09
that increase in bmi is likely because
9:11
of an increase in body fat we also have
9:13
a lot of research that shows that very
9:15
high and very low bmis are associated
9:17
with a greater risk of dying from
9:19
diseases like heart disease and diabetes
9:22
just in general so putting all of that
9:24
together we can see that bmi is a useful
9:26
tool for looking very basically at how
9:29
body weight is related to health in the
9:32
general population over time it is by no
9:35
means a complete tool and it is not very
9:38
useful for giving us a complete idea of
9:40
an individual's health and don't forget
9:42
that having a very low bmi puts people
9:45
at a greater risk of sickness and death
9:47
too so it's important to remember that
9:49
there's probably a sweet spot of bmi
9:51
that can vary a lot between people so
9:54
does all this make sense i hope this
9:57
video helps you understand that bmi
9:58
isn't completely useless but it does
10:00
have a lot of limitations that
10:02
scientists are very aware of and that's
10:04
exactly why there are so many other
10:06
factors to take into account to get a
10:08
better picture of an individual's health
10:10
as always if you have any questions let
10:12
me know in the comments below and
10:13
remember to like and subscribe to the my
10:15
protein youtube channel for more great
10:17
evidence-based nutrition information
10:21
[Music]
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