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Volume 15 Number 2
July-December, 2015
ISSN 1596-4078
NIGERIAN JOURNAL OF HEALTH SCIENCES . Volume 15 . Number 2 . July-December, 2015 . Pages 69-***
Nigerian Journal
of Health Sciences
ISSN 1596-4078
Official Publication of the
College of Health Sciences,
Obafemi Awolowo University, Ile-Ife, Nigeria
&
Obafemi Awolowo University Teaching Hospitals Complex,
Ile-Ife, Nigeria
Original Article
Challenges of Body Mass Index Classification: New Criteria for
Young Adult Nigerians
Ogunlade O, Adalumo OA, Asafa MA
Department of Physiological Sciences, Faculty of Basic Medical Science, Obafemi Awolowo University, Ile‑Ife, Osun‑State, Nigeria
ABSTRACT
Background: There are evidences to suggest that the World Health Organization (WHO) general cutoff points for body mass index (BMI) may
not be the most appropriate for young adults globally irrespective of racial and ethnic considerations.
Objective: This study assessed body anthropometric parameters in healthy population of young adult Nigerians with a view to determining race
and gender-speciic criteria (Ife criteria) for BMI classiication.
Methods: Four hundred and eighty-four (242 males and 242 females) healthy subjects aged between 18 and 41 years (inclusive) were recruited
for the study. The participants were age- and sex-matched (mean age: 22.81 ± 3.83 years). The weight and height of the subjects were obtained
using standard techniques while BMI was calculated as derivatives of height and weight. The BMI was classiied using 5th, 85th, and 95th percentiles
and delineated into underweight (<5th percentile), normal (5–85th percentile), overweight (85–95th percentile), and obese (>95th percentile).
Results: The result showed that the general BMI cutoff values for underweight, normal, overweight, and obesity were <17.8, 17.8–24.7,
24.8–27.8, and ≥27.9, respectively. The sex-speciic BMI cutoff values for underweight, normal, overweight, and obesity in males and females
were < 17.8 and < 17.8; 17.8–23.6 and 17.8–25.6; 23.7–26.8 and 25.7–28.7; and ≥26.9 and ≥28.8, respectively.
Conclusions: The cutoff values for the new criteria for BMI classiication were lower than the WHO deined values and sex differences were
demonstrated in BMI. Therefore, WHO criteria may not be universally applicable.
Key words: Body mass index, challenges, classiication, new criteria
How to cite this article: Ogunlade O, Adalumo OA, Asafa MA. Challenges of body mass index classiication: New criteria for young adult Nigerians. Niger
J Health Sci 2015;15:71-4.
INTRODUCTION
Body mass index (BMI) is an estimation of the proportion of
body weight that is accounted for by fat. BMI is calculated as
body mass in kilograms divided by square of height in meters.1
Hence, BMI is derivative of weight and height. According to
World Health Organization (WHO) general cutoff points, BMI
could be used to classify individuals into four major categories;
underweight (<18.5 kg/m 2), normal (18.5–24.9 kg/m 2),
overweight (25–29.9 kg/m2), and obese (≥30 kg/m2).2 BMI
as defined simply applies to people with “normal body
frame.” It is less useful for fat estimation among athletes and
weightlifters. This is because these individuals have their
body frame mostly contributed by bone and muscle rather
than increased fat accumulation. BMI measures and quantiies
the degree of excess body weight and not strictly excess body
fat. Hence, athletes and many muscular or “physically it”
individuals can be overweight without signiicant accumulation
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of body fat.3 BMI is slightly increased in the elderly and to a
lesser extent in children.4,5
The world is diverse in population and various regions of
the world are made up of many and different ethnic groups
with distinct genetic constitutions. Therefore, different ethnic
groups have different physiological responses to fat storage.6
BMI cutoff points have been ixed by the WHO based on
classiications in a number of past studies based on mortality
and morbidity outcomes and body build in the USA and
Europe.6 There were evidences to support the fact that the BMI
and body fat accumulation differs among ethnic populations.7
As far back as the year 2000, the Regional Ofice for Western
Pacific of WHO (WPRO), the International Association
for the Study of Obesity, and the International Obesity
Task Force jointly put forward a separate classiication for
Address for correspondence: Dr. Ogunlade O,
Department of Physiological Sciences, Faculty of Basic Medical
Science, Obafemi Awolowo University, Ile‑Ife, Osun‑State, Nigeria.
E‑Mail: oogunlade@oauife.edu.ng
Website:
www.chs-journal.com
DOI:
10.4103/1596-4078.182319
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71
Ogunlade, et al.: New Criteria for BMI Classiication
obesity among Asian populations.7 In their classiications,
overweight was speciied as a BMI over 23.0 and obesity as
a BMI over 25.0. Sequel to what the WPRO put forward, the
Examination Committee of the Japan Society for the study
of obesity followed with a new guideline for diagnosing
“obesity” and set obesity as a BMI >25.8 Moreover, the new
BMI criteria for Asians by the Western Paciic Region of the
WHO have since being in use for medical clinical screening
within the Asian populations. The suitability of the WPRO
criteria in the screening for overweight to prevent metabolic
syndrome in elderly Japanese workers had been established.9
Issues regarding BMI criteria and its cutoff points should,
therefore, be of public health concern globally. To date,
there has been little or no reported study, or attempt geared
toward the categorization of BMI cutoff points by the African
Regional Ofice of the WHO among indigenous Africans.
Our goal therefore was to determine the BMI cutoff points
among Nigerian young adults as well as determining gender
differences in the criteria among the study population. This
study assessed the body anthropometric parameters in healthy
population with a view to deining race speciic new BMI
criteria called Ife BMI Criteria for young adults.
METHODS
Participants
Four hundred and eighty-four (242 males and 242 females)
subjects aged between 18 and 41 years were recruited for
the study. They were selected according to their age and
sex. They were grouped into four age group categories;
18–23 years (69.0%), 24–29 years (24.4%), 30–35 years (4.5%),
and 36–41 years (2.1%). The study population was drawn from
people within Ilé-Ifẹ̀, an ancient Yoruba town in South-Western
Nigeria. Only healthy volunteers (absence of systemic
diseases) after initial screening process participated in the
study. The screenings include clinical evaluation and blood
pressure assessment. Exclusion criteria were symptomatic
diseases, pedal edema, pregnancy, athlete, and arterial blood
pressure ≥140/90 mmHg. The volunteers were assessed for
anthropometric parameters, height and weight while their
BMI calculated.
Ethical consideration
Participation in the study was completely voluntary based on
informed consent from the participants. Ethical clearance was
sought and obtained from the Ethics and Research Committee
of Obafemi Awolowo University Teaching Hospitals Complex,
Ile-Ife, as anthropometry component of the study of young
adult electrocardiogram.
Height and weight measurements
The standing heights were measured using a stadiometer
(ZT-120 Health Scale). Each participant was assessed while
in good standing posture on the foot rest of the device with
minimal clothing without shoes but with the head facing
forward, shoulders relaxed, arms hanging loosely on both
sides, palms facing forwards, feet together, and knees straight.
72
The height for each subject was taken when the movable
headboard was lowered to touch the crown of the head. The
measurements were taken to the nearest 0.5 cm. The weighing
scale was checked for zero balance before each use. Subjects
were instructed to empty pockets and remove shoes and any
apparel that could interfere with weight measurements. Only
light clothing was permitted. The subjects then stood on the
scale looking straight ahead, relaxed, and motionless without
leaning on any object or the wall. Weight measurements were
taken when the scale stabilized and recorded to the nearest
0.5 kg.
Calculation of body mass index
BMI was calculated as weight in kilograms divided by the
square of height (in meters). BMI was expressed in kg/m2.
Statistical analysis
The data obtained during the investigation were analyzed
using SPSS ® IBM Corporation Software Package. The
descriptive statistics were expressed as a mean ± standard
deviation for each variable. Student’s t-test was carried
out to detect the gender differences for each parameter:
Height, weight, and BMI. A P < 0.05 was considered
statistically significant. The BMI was classified using
5 th , 85 th , and 95 th percentiles and delineated into
underweight (<5th percentile), normal (5–85th percentile),
overweight (85–95th percentile), and obese (>95th percentile).
RESULTS
Body anthropometric parameters
Four hundred and eighty-four young adults participated in
the study. The age range of the participant was 18–41 years.
Among all participants (n = 484), the mean values (normal
limits) for height, weight, and BMI were 1.67 ± 0.09 m
(1.54–1.82 m), 60.94 ± 9.60 kg (47.00–79.75 kg), and
21.82 ± 3.02 kg/m2 (17.80–4.83 kg/m2), respectively. In
anthropometric parameters, men had signiicantly higher
values for height and weight, but they had a signiicantly
lower value for BMI. Among male participants (242), the
mean values for height, weight, and BMI were 1.72 ± 0.07 m,
63.43 ± 9.1 kg, and 21.43 ± 2.63 kg/m2, respectively. Among
female participants (242), the mean values for height,
weight, and BMI were 1.62 ± 0.07 m, 58.46 ± 9.45 kg, and
22.21 ± 3.33 kg/m2, respectively [Table I].
Comparison between new body mass index criteria and
World Health Organization criteria
The new BMI classes of participants from our study
were presented in Table II side-by-side with WHO and
WPRO classifications. The cutoff point for underweight
(<17.8 kg/m 2 ) was lower than the WHO and WPRO
classiication of <18.5 kg/m2. The normal range from this study
was 17.8–24.7 kg/m2 compared to the WHO higher values of
18.5–24.9 kg/m2 and WPRO of 18.5–22.9 kg/m2, respectively
[Table II]. Overweight was determined to be in the range
of 24.8–27.8 kg/m2 and was lower compared to WHO values
Nigerian Journal of Health Sciences ¦ Jul-Dec 2015 ¦ Volume 15 ¦ Issue 2
Ogunlade, et al.: New Criteria for BMI Classiication
of 25.0–29.9 kg/m2 but was higher, compared to WPRO values
of 23.0–24.9 kg/m2. Obesity was determined to be ≥27.9 kg/m2.
Sex‑specific new body mass index cutoff points
The BMI classes of participants by gender were presented in
Table III. Men had lower cutoff values for BMI than women.
Men and women were classiied <17.8 kg/m2 as “underweight,”
17.8–23.6 kg/m 2 and 17.8–25.6 kg/m 2 as “normal,”
23.7–26.8 kg/m2 and 25.7–28.7 kg/m2 as “overweight,”
≥26.9 kg/m2 and ≥28.8 kg/m2 as “obese,” respectively based
on the new criteria [Table III].
DISCUSSION
Our study revealed that the current general cutoff points of
BMI (30 kg/m2 or above) recommended by the WHO might
exceed proper limits. We found this to be higher and tends
to misclassify those who at high risk to be either normal or
at low risk. In the general population, the WHO classiies an
individual to be overweight if the BMI is calculated to be within
25–29.9 kg/m2 and obese if the BMI is ≥30 kg/m2. The results
Table I: Sex differences in age, anthropometry, and body
mass index
Variables
Mean±SD
Male (n=242)
t
P
Female (n=242)
Age (years)
22.81±3.88
22.81±3.88
0.000
1.000
Height (m)
1.72±0.07
1.62±0.07
5.901
<0.001
Weight (kg)
63.43±9.11
58.46±9.45
15.032 <0.001
BMI (kg/m2)
21.43±2.63
22.21±3.33
−2.830
0.005
P<0.05 is taken as statistically signiicant. Signiicant sex differences
exist in height, weight, and BMI. BMI: Body mass index, SD: Standard
deviation
Table II: Body mass index classification according to Regional
Office for Western Pacific of World Health Organization,
New (Ife) and World Health Organization criteria
Category
WPRO
New (Ife) criteria*
WHO
Underweight
<18.5
<17.8
<18.5
Normal
18.5-22.9
17.8-24.7
18.5-24.9
Overweight
23.0-24.9
24.8-27.8
25.0-29.9
Obesity
≥25.0
≥27.9
≥30.0
*New (Ife) criteria for both sexes. WHO: World Health Organization,
WPRO: Regional Ofice for Western Paciic of WHO, BMI: Body mass
index
Table III: New (Ife) body mass index criteria sex‑specific
cutoff points for young adults
Category
Male
Female
Underweight
<17.8
<17.8
Normal
17.8-23.6
17.8-25.6
Overweight
23.7-26.8
25.7-28.7
Obesity
≥26.9
≥28.8
The cut-off points for various categories of BMI were lower in males than
females except for the underweight category. BMI: Body mass index
of this study indicated that the BMI cutoff value was lower
in the population from which our study was carried out. An
individual is overweight if the BMI is within 24.8–27.8 kg/m2
and obese if the BMI is above 27.9 kg/m2. For instance, some
individuals classiied as overweight according to WHO cutoffs
actually falls within the obese class.
Evidence abound against using a single universal cutoff value
worldwide to deine obesity is widespread.10-12 For example,
WHO recommended BMI values of 23 kg/m2 and 25 kg/m2
as the cutoff points for overweight and obesity for Asians,
respectively which is lower when compared with the cutoff
values from our study.7 This may explained in part because
BMI is established to be skewed by height, BMI will be
higher for some Black ethnic groups, and lower for Asian
groups.7 Furthermore, several Asian countries have also
recommended using lower cutoff values to identify overweight
and obesity.13-20 Our indings suggest adequate grounds for
the proposition of separate criteria among Africans of Yoruba
speaking people of South-Western Nigeria. By comparison,
the BMI criteria determined from our study are higher than
WPRO criteria for Asians and lower than the WHO criteria
for the general population.
Gatineau and Mathrani6 postulated that the estimated burden
of obesity-related disease among minority ethnic groups in
the United Kingdom may be greatly underestimated and that
using revised thresholds for some ethnic groups could greatly
increase these estimates. This agrees with our indings with
regards to public health, the estimated burden of obesity-related
diseases among Nigerian ethnic groups may have been
seriously underestimated.
We also established from our indings, the existence of sex
differences in the BMI cutoff points. Even though the WHO
classiication did not take gender differences into account,
our result deines overweight among female participants to
be 25.7–28.7 kg/m2 and obesity to be ≥28.8 kg/m2. This is
higher than in males from our study population which was
23.7–26.8 kg/m2 for overweight category and ≥26.9 kg/m2
for obesity. The observation that BMI cutoff values are higher
in the female is supported by the indings of Hedley et al.,21
which posited that reproductive-aged women are more likely
to be obese than similarly aged men, which may make them
vulnerable to cardiovascular disease risk factors and other
obesity-related diseases. This is in consonance with the age
group (18–41 years) of the female participants in our study.
Our results on gender-speciic BMI cutoff values to deine
obesity among women agree with certain studies carried out
even in the US. Rahman and Berenson22 showed obesity as
those with BMI greater or equal to 28.7 kg/m2. This value was
almost same with the cutoff value of 28.8 kg/m2 in this study.
This is also similar to the data of Evans et al.,23 whose cutoff
values for obesity was 28.4 kg/m2 all among black American
women. Moreover, White and Hispanic women have been
shown to demonstrate signiicantly higher percent body fat
for a given BMI than black women.24 This suggests that the
Nigerian Journal of Health Sciences ¦ Jul-Dec 2015 ¦ Volume 15 ¦ Issue 2
73
Ogunlade, et al.: New Criteria for BMI Classiication
BMI cutoff values should not only be lower than the value
currently used but also it should differ by gender and race or
ethnicity, to better assess an individual’s risk of obesity-related
morbidity and mortality. Other studies have indicated that in
some populations there might be differences in BMI across
ethnic lines which support our indings.2,17,25,26 For example,
a study on Asian American anthropometric measurements
found that reducing the cut-point for obesity from 30 kg/m2
to 27 kg/m2 could increase the prevalence of obesity in a
population by as much as 14% points.27 These differences
may require different cut-points for evaluating obesity using
BMI among different ethnic groups. It appears that when
using BMI to classify individuals into no risk, low risk, and
high-risk categories, the gender and ethnic backgrounds should
be taken into consideration.3 Moreover, it had been justiied
that WHO universal cutoff point for obesity increases the
numbers of people at risk for type 2 diabetes mellitus among
Asian American and that a lower BMI cutoff points had been
considered far more appropriate for Asian population to reduce
overweight-associated disease burdens.28
10.
11.
12.
13.
14.
15.
16.
CONCLUSIONS
In conclusion, the cutoff values for the new criteria for BMI
classiication were lower than the WHO deined values and
sex differences were demonstrated in BMI. Therefore, WHO
criteria may not be universally applicable. Hence, race, age,
and gender should be taken into consideration in determining
the cutoff values for BMI.
Financial support and sponsorship
17.
18.
19.
Nil.
Conflicts of interest
20.
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There are no conlicts of interest.
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