**4. Obesity**

Obesity, by definition, is an excess of body fat that poses a risk to health. It is assessed clinically via the expression of body weight as a function of height – the body mass index (BMI). This is calculated by dividing an individual's weight (in kilograms) by the square of their height (in meters) (kg/m2 ) [3, 24]. BMI is used in adults to delineate overall body fatness where a BMI of 18.5–24.9 kg/m2 is considered to be normal. Abnormal BMI's are sub-categorized according to severity, where a BMI ≥ 25 kg/m2 is considered to be within the overweight range, BMIs ≥30 kg/m<sup>2</sup> are considered as obesity and BMI ranges ≥40 kg/m2 are classified as severe/morbid obesity. Obesity is, however, regarded as a disease of opulence, easily remedied by the reduction of food intake and considered to be irrelevant elsewhere. Furthermore, obesity was not a major concern for the WHO as their priority was to deal with malnutrition and the problems of the third world. By the mid-1990's, obesity had become a prominent problem for obesity specialists but was still not being taken seriously by most national governments. The prevalence is generally higher in women than in men, although the highest incidence was recorded in males aged 25–29 years residing in low-middle income countries.

## **4.1 Causes of obesity**

Obesity is an unintended consequence of a 'Western lifestyle' [25] where economic, social and technological advances [26] have resulted in urbanization and reduced physical activity [27]. Diets have transitioned from natural, organic foods to refined, high fat and high sugar alternatives, leading to a nutrition transition parallel to the observed economic growth [28]. These changes have led to a rapid increase in the prevalence of obesity [25]. As a historically Western disease, obesity was largely localized to developed countries until recent decades where middle- and low income-countries began to experience rates comparable to those of highincome countries. The rapid economic expansion and modernization experienced

by middle- and low-income countries, as well as changing diets, are the greatest contributors to this epidemic [28] as more and more of these countries adopt Western diets and lifestyles. Close to 30% of the populations within middle income countries are classified as overweight or obese, with South Africa (SA) having the highest prevalence in sub-Saharan Africa, where the prevalence was reported to be 27% in adults over the age of 18 years in 2016 [29]. While the predominant causes of the energy imbalance seen in obesity are inadequate physical activity and unhealthy diets, not all those who are exposed to these unfavorable behaviors will develop the disease. Obesity arises from the interactions between an at-risk genetic profile and environmental risk factors, such as physical inactivity, excessive caloric intake, the intrauterine environment, medications, socioeconomic status, and possibly novel factors such as insufficient sleep, endocrine disruptors, and the gastrointestinal micro biome [30]. Obesity is a multifactorial disease, and many underlying factors disproportionately predispose subsets of the population to its development, and several of these are non-modifiable factors including age, gender, race, and genetics. Specific structural and functional changes are observed in obese visceral adipose tissue, together with local inflammation and adipokine production, promoting metabolic disturbances [31, 32]. Obesity leads to the presence of ectopic fat surrounding organs and to the accumulation of lipids in tissues themselves. Peripancreatic adipose tissue is implicated in glucose homeostasis regulation and can be impaired in obesity.
