Obesity

Introduction

Obesity may be defined as an abnormal growth of adipose tissue resulting from an enlargement of fat cell size, known as hypertrophic obesity, or an increase in the number of fat cells, referred to as hyperplastic obesity, or a combination of both. Obesity is commonly expressed in terms of Body Mass Index (BMI). Overweight is usually due to obesity, but it may also arise from other causes such as abnormal muscle development or fluid retention and therefore does not always indicate excess body fat.

Obese individuals differ not only in the total amount of excess fat stored in the body but also in the regional distribution of this fat. The pattern of fat distribution associated with weight gain significantly influences the health risks related to obesity and determines the type of diseases that may develop. Therefore, it is useful to distinguish individuals with increased risk due to abdominal fat distribution, also known as android obesity, from those with the less serious gynoid pattern of fat distribution, in which fat is more evenly and peripherally distributed around the body, particularly over the hips and thighs.

Prevalence

Obesity is one of the most prevalent forms of malnutrition worldwide, affecting both developed and developing countries and occurring among children as well as adults. Since 1990, the prevalence of overweight and obesity has more than doubled globally. In 2022, an estimated 2.5 billion adults aged 18 years and older were overweight, including over 890 million adults living with obesity. Approximately 16% of adults worldwide were obese in 2022. Childhood obesity has also shown a dramatic rise, increasing four-fold between 1990 and 2022. Overweight and obesity are now major contributors to non-communicable diseases (NCDs) such as diabetes mellitus, cardiovascular diseases, and certain cancers, and they represent a leading risk factor for global morbidity and mortality.

In India, the prevalence of overweight and obesity has increased sharply across all age groups. Among children and adolescents aged 5–19 years, rates of overweight and obesity have risen multiple folds from the early 2000s to 2022. Among adults, data from the National Family Health Survey (NFHS) 2019–21 show that the prevalence of overweight and obesity among both men and women has nearly doubled compared to previous decades, indicating a nationwide rise in unhealthy body weight across the life course.

According to the Nepal Demographic and Health Survey (NDHS) 2022, as reported to the World Health Organization (WHO), the prevalence of overweight among children under five years was 1.3%, indicating that childhood overweight remains low in Nepal. However, adult overweight and obesity are emerging as growing public health concerns. The WHO Global Obesity Observatory places Nepal among lower-middle-income countries with rising adult obesity, reflecting nutritional transition, urbanization, and lifestyle changes. NDHS 2022 data show a dual burden of malnutrition among women aged 15–49 years: 26% of adolescent girls (15–19 years) were thin, while 6% were overweight or obese; among women aged 20–49 years, 35% were overweight or obese, compared to 10% who were thin. Overweight and obesity were more common in urban areas (38%) than rural areas (26%) and increased with household wealth, from 20% in the poorest to 53% in the richest households.

Epidemiological determinants

Age: Obesity can occur at any stage of life, but its prevalence generally increases with advancing age. Infants who experience excessive weight gain are at a greater risk of becoming obese in later life, and about one-third of obese adults have been obese since childhood. Most adipose cells are formed early in life; therefore, obese infants tend to develop a higher number of fat cells, leading to hyperplastic obesity, which is particularly difficult to treat during adulthood.

Sex: Women generally have higher rates of obesity compared to men, although men often show higher rates of overweight. Studies such as the Framingham Heart Study have demonstrated that men tend to gain maximum weight between the ages of 29 and 35 years, whereas women gain most weight between 45 and 49 years, especially during menopause. Body mass index may increase slightly with successive pregnancies; however, in many developing countries, closely spaced pregnancies are often associated with weight loss rather than weight gain.

Genetic factors: Genetic factors play an important role in the development of obesity. Evidence from twin studies shows a strong correlation in body weight among identical twins, even when they are raised in different environments. Fat distribution patterns also exhibit significant heritability, accounting for nearly 50 percent of individual variation. In particular, abdominal or central fat accumulation is strongly influenced by genetic predisposition.

Physical activity and sedentary lifestyle: There is strong evidence that regular physical activity protects against unhealthy weight gain, while sedentary lifestyles promote obesity. Inactive occupations and leisure activities such as prolonged television viewing reduce energy expenditure and increase the risk of weight gain. Reduced physical activity is now considered more important in the causation of obesity than previously thought. Physical inactivity may lead to obesity, which in turn further limits physical activity, creating a vicious cycle.

Socio-economic status: Socio-economic status shows an inverse relationship with obesity in many populations. In several affluent countries, obesity is more common among individuals from lower socio-economic groups. Factors such as limited access to healthy foods, lack of awareness, and unhealthy living conditions contribute to this pattern, increasing the risk of obesity.

Dietary habits: Dietary habits established early in life play a major role in the development of obesity. Frequent snacking, high consumption of sweets, refined foods, and fats contribute significantly to excessive calorie intake. The increased availability and aggressive promotion of energy-dense foods through advertising and mass media further encourage unhealthy eating behaviors and weight gain.

Psychosocial factors: Psychosocial factors such as emotional stress, depression, anxiety, and loneliness are closely associated with overeating and obesity. Emotional eating often leads to increased intake of high-calorie foods, contributing to positive energy balance and gradual weight gain over time.

Family history and environment: Obesity often runs in families due to a combination of shared genetic factors and common environmental influences. Family members tend to adopt similar dietary habits, physical activity patterns, and lifestyle behaviors, all of which contribute to an increased risk of obesity.

Endocrine factors: Certain endocrine disorders contribute to obesity in a small proportion of individuals. Conditions such as Cushing’s syndrome and growth hormone deficiency lead to metabolic disturbances that promote fat accumulation and weight gain.

Alcohol consumption: Alcohol intake is generally associated with increased adiposity, particularly among men. Alcohol provides excess calories and may stimulate appetite, leading to increased energy intake and fat deposition.

Education: In most affluent societies, there is an inverse relationship between educational level and prevalence of overweight

Ethnicity: Ethnic groups in many industrialized countries appear to be especially susceptible to the development of obesity and its complications. Evidence suggests that this may be due to a genetic predisposition to obesity that only become apparent when such groups are exposed to a more affluent lifestyle

.Drugs: Use of certain drugs, e.g., cortico-steroids, contraceptives, insulin, ß-adrenergic blockers, etc. can promote weight gain.

Use of BMI to classify obesity

Body Mass Index is a simple and widely used measure to classify underweight, overweight, and obesity in adults. It is calculated as weight in kilograms divided by the square of height in metres. Obesity is defined as a BMI of 30 kg/m² or more. Although BMI correlates with mortality risk, it does not distinguish between fat mass and lean body mass, and the same BMI may represent different levels of body fat across populations, ages, and sexes.

Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, overweight, and obesity in adults. It is defined as a person’s weight in kilograms divided by the square of their height in metres (kg/m²).

For example, an adult who weighs 70 kg and has a height of 1.75 m will have a BMI of 22.9:

BMI = 70 (kg)/l.75² (m²) = 22.9

Classification of adults according to Body Mass Index (BMI)

BMI (kg/m²)	Nutritional status
< 18.5	Underweight
18.5 – 24.9	Normal weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obesity Class I
35.0 – 39.9	Obesity Class II
≥ 40.0	Obesity Class III (Morbid obesity)

Note: This classification is recommended by the World Health Organization (WHO) and is widely used for assessing obesity-related health risks in adults aged 18 years and above.

Intra-abdominal fat and health risk

Intra-abdominal adipose tissue differs metabolically from subcutaneous fat. It has greater blood flow, more hormone receptors, and higher rates of lipolysis. Fatty acids released from this tissue reach the liver directly through the portal circulation, contributing to insulin resistance, dyslipidaemia, and metabolic syndrome. Abdominal obesity is strongly linked to cardiovascular disease and diabetes.

Assessment of obesity

Before considering the assessment of obesity, it is useful to first understand body composition, which includes the following components:
(a) Active mass – muscles and vital organs such as the liver, heart, and kidneys;
(b) Fatty mass – body fat stored in adipose tissue;
(c) Extracellular fluid – blood, lymph, and interstitial fluid;
(d) Connective tissue – skin, bones, and other supporting tissues.

Structurally, the state of obesity is characterized by an increase in the fatty mass at the expense of other components of the body. The total body water content is not increased in obesity, which helps differentiate it from conditions such as edema.

Although obesity can often be identified at first sight, accurate assessment requires standardized measurements and reference standards. The most widely used criteria are described below.

1. Body weight: Body weight, although not an accurate measure of excess body fat, is a commonly used index, especially in epidemiological studies.

• In population studies, obesity is defined as body weight exceeding +2 standard deviations (SD) from the median weight for height.
• Body weight alone cannot differentiate between fat mass and lean body mass, limiting its use for individual diagnosis.

2. Weight-for-Height Indices

(a) Body Mass Index (BMI) / Quetelet’s Index

BMI is the most widely used indicator for assessing obesity in adults.

BMI = Weight (kg) / [Height (m)]²

Classification (WHO):

• < 18.5 kg/m² – Underweight
• 18.5–24.9 kg/m² – Normal
• 25.0–29.9 kg/m² – Overweight
• ≥ 30.0 kg/m² – Obese

BMI is simple, inexpensive, and useful for both clinical and community surveys, though it does not reflect body fat distribution.

b) Ponderal Index

Ponderal Index=Weight (kg) / [Height (m)]³

It is less commonly used than BMI but may be helpful in assessing body build.

3. Skinfold thickness

• Skinfold thickness measures subcutaneous fat using calipers.
• Common sites include triceps, biceps, subscapular, and suprailiac regions.
• The values are compared with standard reference charts to estimate body fat.

Requires skilled personnel and is less accurate in very obese individuals.

4. Waist circumference

Waist circumference measures central (abdominal) obesity, which is strongly associated with metabolic and cardiovascular diseases.

• Measured midway between the lower rib margin and the iliac crest.
• It is considered a better predictor of health risk than body weight alone.

5. Waist–Hip Ratio (WHR)

The Waist-Hip Ratio (WHR) is a valuable indicator of body fat distribution and a potential predictor of health risks associated with obesity [1, 2]. As the formula suggests, it is a simple calculation:

WHR= Hip Circumference/Waist Circumference​

• Indicates fat distribution in the body.
• A higher WHR suggests android (apple-shaped) obesity, which carries greater health risk.

Hazards of obesity

Obesity is a significant health hazard and a detriment to overall well-being, as it is associated with increased morbidity and mortality.

(a) Increased morbidity

Obesity is a positive risk factor for several chronic diseases, including hypertension, diabetes mellitus, gallbladder disease, coronary heart disease, and certain types of cancers, particularly hormonally related cancers and large bowel cancer. In addition, obesity is associated with non-fatal conditions that contribute to considerable morbidity in the community, such as varicose veins, abdominal hernia, osteoarthritis of the knees, hips, and lumbar spine, flat feet, and psychological stress, particularly during adolescence.

Obese individuals are also exposed to increased risks during surgery and may experience reduced fertility

(b) Increased mortality

The Framingham Heart Study in the United States demonstrated a marked increase in sudden death among men who were more than 20% overweight compared to those with normal weight. The increased mortality is primarily due to the higher incidence of hypertension and coronary heart disease, but there is also an excess risk of deaths from renal diseases. Overall, obesity contributes to a lowered life expectancy.

Prevention and control

 Obesity is associated with several health problems, including low back pain due to excess body weight, increased risk of complications during anaesthesia, and fetal defects and adverse pregnancy outcomes associated with maternal obesity.

Weight control is broadly defined as approaches to maintaining body weight within the healthy (normal or acceptable) Body Mass Index (BMI) range of 18.5–24.9 kg/m² throughout adulthood (WHO Expert Committee, 1995). It also includes the prevention of weight gain of more than 5 kg in all individuals. In persons who are already overweight, an initial reduction of 5–10 per cent of body weight is recommended, as this degree of weight loss provides significant health benefits.

Prevention of obesity should begin early in childhood, since obesity is more difficult to treat in adults than in children. The control of obesity mainly centres around weight reduction, which can be achieved through dietary changes, increased physical activity, or a combination of both.

(a) Dietary changes

Dietary modification is essential for both the prevention and treatment of obesity. The proportion of energy-dense foods, particularly those rich in simple carbohydrates and fats, should be reduced. The fibre content of the diet should be increased through the consumption of common unrefined foods. Adequate levels of essential nutrients must be ensured, even in low-energy diets; most conventional weight-reduction diets for adults are based on an intake of about 1000 kcal per day. Reducing diets should be planned as close as possible to the individual’s usual dietary pattern to ensure better compliance. The basic principle is that energy intake should not exceed energy expenditure. Successful dietary control requires behavioural modification and strong motivation to lose weight and maintain ideal body weight. However, most attempts to reduce weight through dietary advice alone are often unsuccessful.

(b) Increased physical activity

Increased physical activity is an important component of any weight-reduction programme. Regular physical exercise is the key factor in increasing energy expenditure, helping in weight loss and maintenance of ideal body weight. Physical activity also improves overall health and reduces the risk of obesity-related complications. When combined with dietary modification, physical activity significantly enhances the effectiveness of obesity control.

(c) Other measures

Other measures in the control of obesity include pharmacological and surgical interventions, though their role is limited. Appetite-suppressing drugs have been used but are generally inadequate to produce substantial and sustained weight loss, especially in severely obese individuals. Surgical treatments such as gastric bypass, gastroplasty, and jaw wiring, which aim to restrict food intake, have also been tried but have shown limited success and are associated with risks. Therefore, one should not expect quick or tangible results from obesity prevention programmes.

Health education plays a crucial role in teaching people how to reduce overweight and prevent obesity. A particularly effective approach is to identify children who are at risk of becoming obese and to implement early preventive measures.

References

1. Park, K. (2025). Park’s textbook of preventive and social medicine (28th ed.). Banarsidas Bhanot Publishers.
2. World Health Organization. (2024, June 3). Obesity and overweight. WHO. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
3. UNICEF India. (2023, July 12). India: Overweight and obesity rising across all ages – from youngest children to adults. UNICEF. https://www.unicef.org/india/press-releases/india-overweight-and-obesity-rising-across-all-ages-youngest-children-adults