Obesity

Obesity increases the risk of many diseases#

Fat accumulates in our bodies when the energy (kilojoules) we take in from food and drink is greater than the energy we use during activity and at rest. Taking in even slightly more energy than you use, over long periods of time, can lead to becoming overweight or obese.

Overweight and obesity are rising in many parts of the world. They contribute to non-communicable diseases such as heart disease, cancer and diabetes, which are now among the world’s leading causes of death. Rates of overweight and obesity have continued to climb over recent decades among both adults and children.

How body size is measured#

Body mass index (BMI) is a measure of body size used to indicate the level of risk for illness (morbidity) and death (mortality) at the population level. The World Health Organization uses BMI to define overweight and obesity. BMI is calculated by dividing your weight in kilograms by your height in metres squared.

For example, a person who is 165 cm tall and weighs 64 kg has a BMI of about 24 kg/m². In general:

• a BMI of 25 kg/m² or more is classified as overweight
• a BMI of 30 kg/m² or more is classified as obese

BMI charts should be used only as a guide to indicate when small lifestyle changes may help, and when to seek further advice from a doctor or dietitian. For children, a doctor or dietitian assesses weight using a special BMI chart for children and teenagers, together with weight and height growth charts. If you have concerns about your child’s weight, it is best to consult a dietitian or doctor for personalised advice.

Abdominal obesity and waist circumference#

The way fat is distributed also matters when assessing health risk. Increased fat around the abdomen is linked to a higher risk of conditions such as cardiovascular disease, type 2 diabetes and some cancers.

For adults, it is helpful to combine BMI with waist circumference:

• A waist measurement above 94 cm in men and above 80 cm in women indicates overweight and increased risk of serious chronic disease.
• A waist measurement above 102 cm in men and above 88 cm in women indicates obesity.

Obesity and chronic disease#

Obesity increases the risk of many chronic and potentially life-threatening conditions. Generally, the more body fat you carry, the higher your health risk. The amount of weight gained over your adult years also contributes. For example, a middle-aged person who weighs 10 kg more than they did in their early twenties has an increased risk of high blood pressure, stroke, diabetes and coronary heart disease.

Chronic conditions associated with obesity include:

• insulin resistance and type 2 diabetes
• high blood pressure, atherosclerosis, cardiovascular disease and stroke
• some cancers, including breast, endometrial and colon cancer
• gall bladder disease
• polycystic ovarian syndrome
• musculoskeletal problems such as osteoarthritis and back pain
• gout
• cataracts
• stress incontinence
• sleep apnoea

What causes obesity#

A range of factors can contribute to obesity, and factors in childhood and adolescence are particularly influential. A high proportion of children and adolescents with obesity grow up to be adults with obesity. Known contributors include:

• Eating more energy than you use – you accumulate fat when you take in more energy (kilojoules) than you use.
• Modern living – cars, computers, televisions and home appliances all reduce the need to be physically active.
• Long periods of sitting – even people who are physically active have a higher risk of obesity if they spend large amounts of time sitting, for example watching TV, working at a computer or driving.
• Changes in the food supply – energy-dense, nutrient-poor foods and drinks are widely available, heavily marketed and affordable, and portion sizes have grown.
• Inactivity – for many people, physical activity is no longer a natural part of daily life; we drive instead of walk.
• Socioeconomic factors – people with lower levels of education and income are more likely to be overweight or obese.
• Genes – genetics play a small part in regulating body weight, and a parent’s overweight or obesity is associated with increased risk in their child.
• Birth and early-life factors – risk may be higher in people who experienced poor nutrition before birth, exposure to maternal smoking, low birth weight, high birth weight, or formula feeding rather than breastfeeding.

Prevention#

Overweight and obesity are largely preventable. The main steps are to choose healthier, lower-energy foods and drinks, and to be more physically active. Building regular movement back into daily life, watching portion sizes and limiting energy-dense, nutrient-poor foods all help to keep energy intake and use in balance.

Key points#

• Fat builds up when energy taken in exceeds energy used over time.
• Obesity increases the risk of many serious chronic diseases.
• BMI indicates risk at the population level, and is most useful when combined with waist circumference.
• Increased fat around the abdomen is linked to higher risk of cardiovascular disease, type 2 diabetes and some cancers.
• Overweight and obesity are largely preventable through healthier eating and more physical activity.

Where to get help and trusted information#

For evidence-based global health guidance, see Source: World Health Organization (WHO).