Obesity

What is it?

MedlinePlus says: "Obesity is a disease that means having too much body fat", and it is considered present in an adult at a BMI of 30 or above, and severe at 40 or above. According to WHO: overweight in adults is a BMI of 25 or above and obesity 30 or above (BMI = weight in kilograms divided by the square of height in metres). The NIDDK describes the condition as a weight higher than what is considered healthy for height, which raises the risk of many health problems.

The NIDDK says (categories for adults aged 20 and over): 18.5–24.9 healthy weight, 25–29.9 overweight, 30 or above obesity, and 40 or above severe obesity.

The NHS cautions that BMI does not distinguish between muscle and fat, so it may wrongly classify a muscular person, and that waist-to-height ratio is an alternative way of assessing. It uses lower thresholds for people from certain ethnic backgrounds, including South Asian, Chinese, other Asian, Middle Eastern and Black African: overweight 23–27.4 and obesity 27.5 or above. This page does not cover how to apply these thresholds locally.

Prevalence figures: according to WHO, one in 8 people in the world lives with obesity, the number of adults with obesity reached 890 million and with overweight 2.5 billion, and adult obesity more than doubled since 1990. According to the CDC, obesity reached 41.9% of US adults during 2017–March 2020, with severe obesity 9.2%. (CDC and NIDDK figures are for the United States and do not necessarily apply elsewhere.)

Causes

According to WHO: obesity results from "an imbalance between energy in (food) and energy out (physical activity)", with contributions from limited availability of affordable healthy food, few places for physical activity, and weak health system responses.

MedlinePlus lists factors including genetic makeup, eating habits, sex, race or ethnicity, level of physical activity, and certain medicines or medical conditions. The NHS adds: low activity, eating more calories than needed, mental health conditions such as depression, physical disabilities that limit movement, certain medicines (steroids, antidepressants and beta blockers), underlying conditions (thyroid disorders, polycystic ovary syndrome and Cushing's syndrome), genetic predisposition, advancing age and hormonal changes.

This is a multifactorial condition and cannot be reduced to "willpower"; a person is not to blame for genetic, environmental and medical factors like these (editorial wording based on the multiple factors in the sources above).

Risk factors

The factors listed in the causes section (genetic, dietary, environmental, medicinal and medical) are those given in this page's sources.

Symptoms

This page's sources did not mention specific symptoms of obesity itself. The NHS mentions related day-to-day challenges including shortness of breath, fatigue, joint pain and depression.

How is it diagnosed?

Classification is based on body mass index (WHO, NIDDK, MedlinePlus), and the NHS lists waist-to-height ratio as an alternative and recommends seeing a healthcare provider if you are overweight or obese and want support to lose weight, if your waist circumference is more than half your height, if you have diabetes, high blood pressure or sleep apnoea, if there is a family history of obesity, or if an eating disorder is suspected.

Treatment

The treatment categories usually used are listed here; this is not a prescription. The doctor chooses the plan according to each person's condition; do not change any medicine or dose without a specialist.

According to the NIDDK: the main treatment is changing health behaviours, i.e. "following a healthy eating plan and increasing physical activity". Structured programmes designed for the individual, as the NIDDK describes them, include "14 or more counselling sessions over 6 months", an individual eating plan, at least 150 minutes a week of moderate-intensity aerobic activity, daily recording of food and activity, and regular support individually, in groups or online. The NIDDK suggests an initial goal of losing 5% of body weight within 6 months. MedlinePlus states that losing 5–10% of weight may delay or prevent some related diseases. These are the source's figures, not a personal prescription.

The NIDDK mentions medicines "when lifestyle change is not enough", which help with losing weight and keeping it off alongside continued healthy eating and activity. The NHS mentions categories including appetite suppressants (semaglutide, tirzepatide and liraglutide) and a fat absorption inhibitor (orlistat), and WHO refers to recent guidance supporting GLP-1 therapies within comprehensive programmes. The medicine and its suitability are decided with the doctor.

Metabolic and bariatric surgery changes the digestive system; the NIDDK mentions its suitability for those with a BMI of 35 or above, or lower with serious related conditions such as type 2 diabetes and sleep apnoea. The NHS mentions similar criteria (40 or above, or 35 or above with accompanying conditions). Devices are newer options for those for whom others have not worked, and their long-term safety and effectiveness data are limited (NIDDK). MedlinePlus refers to counselling and support groups, and the NHS to weight management programmes with coaching and cognitive behavioural therapy.

Complications

MedlinePlus states that obesity raises the risk of: type 2 diabetes, heart disease, high blood pressure, stroke, metabolic syndrome, osteoarthritis, sleep apnoea, pregnancy and fertility problems, and some cancers. The NHS adds fatty liver and breast, womb and bowel cancers. WHO estimates that a higher-than-optimal BMI caused about 3.7 million deaths from noncommunicable diseases in 2021.

The CDC states that 58% of US adults with obesity have high blood pressure, and about 23% have diabetes (US data).

Related pages here: type 2 diabetes, high blood pressure, stroke, osteoarthritis, fatty liver and depression.

Prevention

According to WHO: at the individual level, exclusive breastfeeding, limiting screen time and a healthy diet; at the system level, "structural, fiscal and regulatory measures to create healthy food environments". MedlinePlus says a lifestyle that includes healthy eating patterns and regular physical activity supports long-term weight management.

Living with it

WHO stresses that obesity is shaped by the environment, the food available and places to be active, not by the individual alone. A healthcare provider helps set realistic goals (MedlinePlus). This page does not cover detailed advice on follow-up after treatment.

Common questions