Prevalence of overweight and obesity in Nigeria: Systematic review and meta-analysis of population-based studies

In Nigeria, several studies have assessed the prevalence of overweight/obesity with different reports. The purpose of this study was to use a systematic review and meta-analysis to analyze these overweight and obesity reports from different locations in Nigeria over the last ten years. In addition, there was a dearth of systematic reviews and meta-analyses on the prevalence, trends, and demographic characteristics of overweight and obesity in the country. This was a systematic review and meta-analysis of cross-sectional population-based studies among adult Nigerians on the prevalence of overweight/ obesity (defined by body mass index) published from January 2010 to December 2020. Relevant abstracts were scrutinized and articles that included adults of all age groups and were not restricted to a particular group of people (e.g. university community) were selected. Each article was scrutinized by more than 2 authors before selection. The prevalence of overweight/obesity among all participants, among men and among women in Nigeria and its 6 geopolitical zones was determined. All analyses were performed using STATA version 14 (Stata Corp. College Station, Texas, USA). Thirty-three studies were selected and the number of participants was 37,205. The estimated prevalence of overweight and obesity was 27.6%, and 14.5% respectively. The prevalence of overweight among men and among women was 26.3% and 28.3% respectively and, the prevalence of obesity among men and women was 10.9% and 23.0% respectively. The prevalence of overweight in the 6 geopolitical zones was Southeast 29.3%, Southwest 29.3%, South-south 27.9%, Northwest 27.2%, North-central 25.3%, Northeast 20.0% and obesity South-south 24.7%, Southeast 15.7%, Southwest 13.9%, Northwest 10.4%, North-central 10.2%, Northeast 6.4%. Egger’s tests showed no statistically significant publication bias among the studies that reported the overweight and obesity prevalence respectively (p = 0.225, P 0.350). The prevalence of overweight/obesity in Nigeria is high. The southern geopolitical zones had a higher prevalence of overweight/obesity.

Introduction that more attention is currently being paid to undernutrition [14]. In order to convince policymakers to pay more attention to overweight and obesity reliable statistics highlighting obesity as a serious public health problem in Nigeria are needed. The goal of this study was to assess the prevalence of overweight and obesity in Nigeria and its six geopolitical zones using data from multiple population-based studies conducted across the country. In addition, we also intended to test the hypothesis that the prevalence of obesity had increased in the last decade when compared to preceding decades. A recent reliable estimate of the prevalence of overweight and obesity among the adult population in the country will contribute to the statistics needed to sway policymakers in the country to take urgent and substantial action on the increasing prevalence of obesity.

Methodology
This was a systematic review and meta-analysis study and the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [15] were adopted and the PRISMA checklist adhered to http://www.prisma-statement.org/. The study focused on overweight and obesity defined by BMI and BMI was classified as follows: overweight, BMI of 25-29.9 kg/m 2 ; and obesity, BMI of 30 kg/m 2 and above [16].

Literature review
A literature search for population-based studies on overweight and obesity, published from January 1, 2010, to December 31st, 2020 on adult Nigerians using the search terms, "obesity" "body mass index" and "overweight". These search terms were used in Google Scholar, PubMed, and Embase search engines to retrieve all potentially relevant English articles. The key search words were combined with Nigeria. Bibliographies of some of the authors were also searched and retrieved abstracts were also scrutinized. In order to eliminate difficulties in analyzing the data, we only paid attention to surveys that made use of BMI in the definition of overweight and obesity, or where both BMI and another method were used only the BMI results were extracted. Waist circumference is another common method of assessing obesity in Nigeria. However, in most studies that were available on abdominal obesity; the protocols for measuring waist circumference were not the same, making it difficult to compare most of the studies. In addition, there is no universally acceptable cut-off criterion for defining abdominal obesity for men and women, due to the existence of different criteria (e.g. The Adult Treatment Panel III and the International Diabetes Foundation) [17]. This is why we focused only on studies that used BMI in defining overweight and obesity.

The criteria for the inclusion of articles
1. The study must be a population-based study with results on the prevalence of overweight.
2. The location of the study in Nigeria must be stated.
3. The period of publication of the study must be within the range of January 1st, 2010 -December 31st, 2020.
4. The study must include adults (18 years of age and older) men and women and people of all ages 5. BMI should be used to stratify overweight and obesity.
6. The study should not be limited to a particular group of people (e.g. factory workers, the university community, or the market community).

Validation of search results
Search results were validated in three stages, as follows: 1. The abstracts of articles on population-based studies on adults found with the above search terms and published between January 1, 2010, and December 31, 2020, were read and those that met the criteria were selected.
2. Abstracts that did not meet the inclusion criteria were discarded.
3. Obtained full-text studies that met the inclusion criteria were reviewed by at least three authors independently and any knotty issue surrounding any article under consideration was discussed by the authors and the final decision on the article was taken by consensus.

4.
A PRISMA flow diagram of steps taken in arriving at the number of included studies was drawn at the end of the screening.

Data extraction
Data extracted from the studies that met the selection criteria included the study community, the geopolitical zone of Nigeria where the study was carried out, year of publication of the article, study design, sample size, mean age (years) of participants in the study, and the prevalence of overweight and obesity among adults in the study based on BMI only.

Statistical analysis
The standard error (SE) and effect size (ES) of the prevalence estimates were calculated using metaprop_one which is the update command of metaprop for performing a meta-analysis of proportions. Heterogeneity chi-square χ 2 test and τ 2 Tau 2 statistic (τ 2 ) was used to assess heterogeneity and the estimate of between-study variance. P-values of less than 0.05 were considered as heterogeneity. The I 2 statistic was also done for each of the pooled estimates to test for variation in ES attributable to heterogeneity. As the differences between the studies were very large (92-98% inconsistency), a random-effects model was used to pool the prevalence of overweight and obesity in Nigeria. Metareg, which performs random-effects meta-regression, was done to assess heterogeneity and combinability. Freeman-Tukey transformations were done to stabilize the geopolitical variances to arrive at the overall prevalence of overweight and obesity in Nigeria. Geopolitical zone-wise pooled estimates weighted by population size in each study place within a given zone (Southeast; South-south, South-west; North-central, Northeast and North-west) for the prevalence of overweight and obesity were also calculated. All analyses were done using STATA version 14 (Stata Corp. College Station, Texas, USA).
from the South-south (SS), 33 from the Southwest (SW), 13 from the North-central (NC), 6 from the Northeast (NE), and 10 from the Northwest (NW) geopolitical zone. Thirty-three articles that fulfilled all the inclusion criteria were finally selected (PRIMA diagram Fig 1).

Study characteristics
The total number of the participants that took part in the 33 included articles was 37,205 (SE = 17,422, SS = 5,313, SW = 8,488, NC = 1,414, NE = 2,822, NW 1,566) The 33 studies were population-based observational cross-sectional designs. They were all community-based studies; however, 2 of the studies were state-wide studies [10,11] and there was no geopolitical zone, regional or nationwide study.  [44][45][46][47]. Five of the 33 studies [19,27,29,32,34] did not report the prevalence of overweight among the participants. The prevalence of overweight and obesity among the men and women genders with the sample sizes of the men and women that took part in the study was reported by 10 and 15 studies, respectively (Table 1).

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Two articles were excluded during the data extraction. One of the articles [48] was from the same community-based study from which an article had been selected [10]. The second study included pregnant women in the study and also excluded people living with diabetes mellitus and other chronic diseases [49].

The prevalence of overweight in Nigeria
The prevalence of overweight from the studies ranged from 12.3% in NW 46 to 41.2% in SS26 geopolitical zones. Heterogeneity was significantly present among the geo-political zones. After stabilizing the regional data using Freeman-Tukey transformations, the overall

Publication bias
The publication bias among studies included for overweight and obesity was determined using the funnel plot and Egger's tests. The results of Egger's tests for the funnel plot showed that there was no statistically significant publication bias in the studies that reported the overweight and obesity prevalence, respectively (p = 0.225 for overweight and p = 0.350 for obesity). (See Figs 6 and 7 for overweight people and Figs 8 and 9 for obese people).

The prevalence of overweight among men and among women in Nigeria
The pooled prevalence of overweight among men and women was determined by 10 studies that met the inclusion criteria.  Tables 4 and S1 and S1 and S2 Figs).

The prevalence of obesity among men and among women in Nigeria
The pooled prevalence of obesity among men and among women was determined by 15 studies. A higher pooled prevalence of obesity was observed among women 23

Discussion
This systematic review and meta-analysis highlighted the prevalence of overweight and obesity among adults in Nigeria and its 6 geopolitical zones based on published studies from January 1, 2010, to December 31, 2020. It is the first systematic review and meta-analysis in the country that delved into the prevalence of overweight and obesity among adults in each of the 6 geopolitical zones in Nigeria from the literature search. The total number of participants that took part in this study was 37,205 and the estimated pooled prevalence of overweight among adults in Nigeria ranged from 12.3% to 41.2% and the prevalence of obesity among adults in Nigeria ranged from 4.0% to 49.3%. In an earlier systematic review [17], the prevalence of overweight

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Prevalence of overweight and obesity in Nigeria: Systematic review and meta-analysis among adults in Nigeria ranged from 20.3%-35.1%, while the prevalence of obesity ranged from 8.1%-22.2%. The observed differences between both studies might be due to the reported rising level of overweight and obesity [3] and also because this study captured more recent studies and covered a wider period.
The estimated pooled prevalence of overweight and obesity among adults in Nigeria in this study was 27.6%, and 14.5% respectively. There is a dearth of systematic reviews and metaanalyses on the prevalence of overweight and obesity in Nigeria. In an earlier meta-analysis

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Nigeria and Ghana were similar which suggested this might be the pattern in the West African region. In a meta-analysis by Kassie et al [4] in Ethiopia, involving published studies on the prevalence of overweight and obesity among adults in Ethiopia covering almost the same period as our study (from January 2010 -March 2020) the estimated pooled prevalence rate of overweight and obesity was 19% and 5.4% respectively. The observed results were much lower than those observed in Nigeria and Ghana (West African countries) and tend to suggest that the prevalence of overweight and obesity among adults in West African countries might be markedly higher than that obtainable in countries in the Horn of Africa. Ofori-arenso et al [51] and Kassie et al [4] also reported an increased prevalence of overweight and obesity in Ghana and Ethiopia respectively. These findings strongly suggest that there is a rapid rise in the prevalence of overweight and obesity in most or all African countries primarily due to lifestyle modifications and other factors. The prevalence rate of overweight and obesity observed among adults in Nigeria in this study was not lower than that reported by the WHO [3] in 2016. This was a pointer that the prevalence of overweight and obesity in Nigeria and some other African countries like Ghana was on par with the WHO [3] reports. The prevalence of overweight among men and among women was 26.3% and 28.3% respectively. In addition, the prevalence of obesity among men and women was 10.9% and 23.0% respectively. These results showed that the prevalence of overweight and obesity was higher among women. These findings were in keeping with those observed by the WHO [3] and

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Prevalence of overweight and obesity in Nigeria: Systematic review and meta-analysis other studies [4,10] from Africa. Magemba et al [52] reported that the use of hormonal contraceptives and marriage were among the risk factors for overweight and obesity among women in Zimbabwe. However, more research is needed to determine the reasons for the difference in the prevalence of obesity between men and women in African countries. This is the first study from the literature search that is reporting the prevalence of overweight/obesity among men and women in Nigeria and there was none to compare our results with from the literature search.
Heterogeneity was observed in the prevalence of overweight/obesity among adults in the 6 geopolitical zones in Nigeria. The prevalence of overweight was (SE 29.3%, SW 29.3%, SS 27.9%, NW 27.2%, NC 25.3%, NE 20.0%) and obesity (SS 24.7%, SE 15.7%, SW 13.9%, NW 10.4%, NC 10.2%, NE 6.4%). In both overweight and obesity, the differences between the regions were statistically significant (p <0.05). The southern geopolitical zones of the country had higher prevalence rates of overweight/obesity when compared to the northern geopolitical zones. However, there was no previous study to compare the results from the literature search. The reasons for the higher prevalence of overweight and obesity in the southern geopolitical zones were multifactorial, and these included higher patronage of fast food in the southern geopolitical zone, increased sedentary lifestyle due to more affluence and industrialization. In addition, differences in dietary habits and a higher level of education in the southern region may also be part of the risk factors.

Conclusion
The prevalence of overweight and obesity in Nigeria was high and had increased over the decades. There is a need to stem the trend because the cost implications are huge. The cost implications of overweight and obesity can be classified as direct or indirect costs. The costs of preventive, diagnostic, and treatment services constitute the direct cost and the cost of morbidity and mortality constitute the indirect cost. Morbidity costs are defined as the income lost from decreased productivity, restricted activity, absenteeism, and hospital admission days. The

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value of future income lost by the premature death of obese patients is known as mortality costs [17]. In the United States, obesity-related medical care costs in 2008, were estimated to be $147 billion and the annual nationwide productivity costs of obesity-related absenteeism ranged between $3.38 billion ($79 per obese individual) and $6.38 billion ($132 per obese individual) [53]. The direct and indirect cost of obesity in Nigeria is not known but is expected to be huge considering the high prevalence of obesity in Nigeria and also the fact that Nigeria is the most populous black nation on Earth. Obesity's increased prevalence in Nigeria, however, is matched by rising levels of obesity's co-morbidities, such as hypertension and diabetes mellitus [54,55]. There is a need for the various levels of governments and other key stakeholders in Nigeria and other African countries to invest more in preventive, diagnostic, and treatment of obesity and its comorbidities.

Limitations
Five out of the 33 selected studies did not report the prevalence of overweight among the study participants. In addition, only 10 and 15 studies adequately reported the prevalence of overweight and obesity, respectively, among men and women in their various study populations.

Recommendation
Based on the high and rising levels of overweight and obesity observed in this study, we urge that policymakers in Nigeria and other sub-Saharan African countries pay more attention to overweight and obesity due to the fact that they pose serious public health problems.   Table. The prevalence of obesity among men and women in population based studies in Nigeria. (DOCX)