CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

Obesity is the accumulation of excess body fat to a degree that can impair health. It is most commonly assessed with the body mass index (BMI), which is weight in kilograms divided by the square of height in metres. By the conventional classification, adults with a BMI of 25 to 29.9 kg/m² are considered overweight, and those with a BMI of 30 kg/m² or above are considered obese (Chukwuonye et al., 2022). Obesity develops when energy intake persistently exceeds energy expenditure, and it is a major risk factor for non-communicable diseases such as type 2 diabetes, cardiovascular disease and some cancers. Once regarded as a problem of rich countries, it is now rising quickly in sub-Saharan Africa.

Nigeria illustrates this change clearly. A systematic review and meta-analysis of population-based studies published between 2010 and 2020 estimated the pooled prevalence of overweight and obesity among Nigerian adults at 27.6 per cent and 14.5 per cent respectively (Chukwuonye et al., 2022). A separate meta-analysis estimated that about 12 million Nigerians aged 15 years and above were obese in 2020, an age-adjusted prevalence of 11.6 per cent (Adeloye et al., 2021). Both studies show a pronounced gender gap. In the first, obesity affected 23.0 per cent of women but 10.9 per cent of men (Chukwuonye et al., 2022). The second likewise found higher rates among women, and higher rates in urban than in rural areas (Adeloye et al., 2021).

The literature links this rise to a wider nutritional and epidemiological transition. Adeloye et al. (2021) attribute it to demographic change, rising incomes, urbanisation, sedentary lifestyles and increased consumption of highly processed foods. These changes affect groups unevenly. Nationally representative studies based on the Demographic and Health Survey (DHS) consistently find that wealthier women are more likely to be overweight or obese. For example, higher wealth, higher education and urban residence were each associated with greater odds of overweight in the 2008 survey (Kandala & Stranges, 2014). In the 2018 survey, the odds of overweight and obesity rose with wealth, while secondary education reduced the odds (Alabi & Badru, 2024). Among female adolescents, household wealth was the only factor that remained significant after controlling for other characteristics (Adeomi & Lawal, 2024).

Geography and culture also appear to matter. The pooled estimates by geopolitical zone show that obesity is most prevalent in the South-South (24.7 per cent) and lowest in the North-East (6.4 per cent), with the remaining zones in between (Chukwuonye et al., 2022). Alabi and Badru (2024) similarly report that southern women have higher odds of overweight and obesity than northern women. They also note that in many African societies, excess body weight has traditionally been seen as a sign of success, wealth and good health. These perceptions can weaken the motivation to control weight, particularly among women.

Obesity is also an economic problem and not just a medical one. Okunogbe et al. (2022) estimate that overweight and obesity cost about 2.19 per cent of global gross domestic product in 2019, through both direct health care costs and indirect costs such as lost productivity, and project that this will rise to 3.29 per cent by 2060 if current trends continue. Although the estimated per capita cost in Africa is currently low relative to other regions, the same study shows that the burden is expected to grow fastest in lower-resource settings. For Nigeria, this implies that rising obesity could increase health expenditure and reduce labour productivity unless its drivers are understood and addressed early. Identifying the socioeconomic factors that shape obesity is therefore a necessary basis for effective public policy.

1.2 Statement of the Problem

The prevalence of overweight and obesity in Nigeria is high and rising, particularly among women and urban residents (Adeloye et al., 2021; Chukwuonye et al., 2022). Excess body weight reduces health and productivity through fatigue, illness, absenteeism and increased demand for health care, and the resulting costs can slow economic progress (Okunogbe et al., 2022). The nutritional transition behind this trend, which includes urban migration, changing dietary preferences, reliance on fast and processed foods and reduced physical activity, is likely to continue to push prevalence upward (Adeloye et al., 2021). Social and cultural attitudes that associate larger body size with prosperity and good health may further delay behavioural change.

Research on the socioeconomic correlates of obesity in Nigeria has expanded, but it has important limitations. First, a large part of the evidence still comes from small-scale studies of specific hospitals, communities or states, whose results cannot be generalised to the whole country. Second, some of the available nationally representative studies concentrate on particular groups, such as women of reproductive age (Alabi & Badru, 2024; Kandala & Stranges, 2014) or female adolescents (Adeomi & Lawal, 2024), and so say little about men. Third, they usually estimate BMI or obesity as the outcome of a single regression or logit equation. This approach may not be adequate if BMI and its socioeconomic correlates, such as wealth and occupation, influence each other. In that case the estimated effects may be biased because of simultaneity.

This study addresses these limitations by analysing the socioeconomic determinants of obesity in Nigeria with nationally representative DHS data, covering men and women, and by using a simultaneous equation framework that takes account of the identification problem. It also tests whether obesity differs across the six geopolitical zones. The results are intended to guide policies that promote healthier lifestyles and reduce the productivity losses associated with obesity.

1.3 Research Questions

The study seeks to answer the following questions:

1. What are the socioeconomic factors that determine obesity in Nigeria?
2. Does obesity vary across the geopolitical zones of Nigeria?

1.4 Objectives of the Study

The broad objective of the study is to investigate the socioeconomic determinants of obesity in Nigeria. The specific objectives are to:

1. identify the socioeconomic determinants of obesity in Nigeria; and
2. examine whether obesity varies across the geopolitical zones of Nigeria.

1.5 Research Hypotheses

The following hypotheses, stated in the null form, are derived from the objectives:

H01: Socioeconomic factors have no significant influence on obesity in Nigeria.

H02: Obesity does not vary significantly across the geopolitical zones of Nigeria.

1.6 Significance of the Study

The study is significant in several ways. First, it provides nationally representative evidence on how wealth, education, occupation, gender and region relate to body mass in Nigeria. This evidence addresses the limitations of studies confined to single locations or to women alone (Adeomi & Lawal, 2024; Kandala & Stranges, 2014).

Second, by identifying the geopolitical zones with the highest levels of obesity, the study can help government and health agencies target prevention programmes where they are most needed. Zonal differences in prevalence are large (Chukwuonye et al., 2022), so blanket national interventions are likely to be less efficient than targeted ones.

Third, the study informs economic and health policy. Because obesity imposes both direct health costs and indirect productivity losses (Okunogbe et al., 2022), evidence on its socioeconomic drivers can support policies on health education, urban planning, food environments and the promotion of physical activity, and can help show whether income distribution matters for health outcomes.

Finally, the study adds to the literature on the nutritional transition in sub-Saharan Africa and offers a methodological reference for later researchers who wish to use simultaneous equation models in health economics.

1.7 Scope of the Study

The study is a cross-sectional analysis based on secondary data from the 2013 Nigeria Demographic and Health Survey (DHS). The dependent variable is obesity, measured by body mass index. The explanatory variables are household wealth, proxied by the DHS wealth index, educational attainment, gender, occupation (in grouped categories), geopolitical region and a lifestyle indicator, the frequency of watching television. Regional differences are captured with dummy variables for the geopolitical zones. The model is estimated with a simultaneous equation approach. The study is limited to the socioeconomic determinants available in the survey and does not examine clinical, genetic or detailed dietary factors.

1.8 Organisation of the Study

The study is organised into five chapters. Chapter One introduces the study, including its background, problem, questions, objectives, hypotheses, significance and scope. Chapter Two reviews the conceptual, theoretical and empirical literature. Chapter Three describes the methodology, including the model specification, data and estimation technique. Chapter Four presents and discusses the results. Chapter Five provides the summary, conclusions and policy recommendations.

1.9 Definition of Terms

Obesity: Excessive fat accumulation that may impair health, identified in adults by a body mass index of 30 kg/m² or above.

Overweight: A body mass index of 25 to 29.9 kg/m².

Body mass index (BMI): A person's weight in kilograms divided by the square of their height in metres.

Wealth index: A composite measure of household living standards in the DHS, built from household assets and housing characteristics.

Socioeconomic determinants: Social and economic characteristics, such as income or wealth, education, occupation, gender and place of residence, that influence health outcomes.

Nutritional transition: The shift from traditional diets and active lifestyles towards energy-dense, processed foods and sedentary behaviour, usually accompanying urbanisation and rising incomes.

References

Adeloye, D., Ige-Elegbede, J. O., Ezejimofor, M., Owolabi, E. O., Ezeigwe, N., Omoyele, C., Mpazanje, R. G., Dewan, M. T., Agogo, E., Gadanya, M. A., Alemu, W., Harhay, M. O., Auta, A., & Adebiyi, A. O. (2021). Estimating the prevalence of overweight and obesity in Nigeria in 2020: A systematic review and meta-analysis. Annals of Medicine, 53(1), 495–507. https://doi.org/10.1080/07853890.2021.1897665

Adeomi, A. A., & Lawal, N. O. O. (2024). Overweight and obesity among female adolescents in Nigeria: An emerging, but under-reported epidemic. BMC Women's Health, 24, 302. https://doi.org/10.1186/s12905-024-03146-4

Alabi, T. A., & Badru, O. A. (2024). Slim north, fat south: Explaining regional differences in abnormal weights in Nigeria. Journal of Biosocial Science, 56(2), 207–231.

Chukwuonye, I. I., Ohagwu, K. A., Ogah, O. S., John, C., Oviasu, E., Anyabolu, E. N., Ezeani, I. U., Iloh, G. U. P., Chukwuonye, M. E., Raphael, C. O., Onwuchekwa, U., Okafor, U. H., Oladele, C., Obi, E. C., Okwuonu, C. G., Iheji, O., Nwabuko, O. C., Nnoli, M. A., & Okpechi, I. G. (2022). Prevalence of overweight and obesity in Nigeria: Systematic review and meta-analysis of population-based studies. PLOS Global Public Health, 2(6), e0000515. https://doi.org/10.1371/journal.pgph.0000515

Kandala, N.-B., & Stranges, S. (2014). Geographic variation of overweight and obesity among women in Nigeria: A case for nutritional transition in sub-Saharan Africa. PLOS ONE, 9(6), e101103. https://doi.org/10.1371/journal.pone.0101103

Okunogbe, A., Nugent, R., Spencer, G., Powis, J., Ralston, J., & Wilding, J. (2022). Economic impacts of overweight and obesity: Current and future estimates for 161 countries. BMJ Global Health, 7(9), e009773. https://doi.org/10.1136/bmjgh-2022-009773