Obesity as a Disease: BMI, Waist and When to Seek Help

Obesity means an amount of body fat that is high enough to harm health. It is recognised as a chronic disease by the World Health Organization and by major medical societies, because it is driven by biology (appetite hormones, genes, the brain’s weight regulation) as well as by food, activity, sleep, stress, medicines and the environment. In 2025 an international Lancet Commission proposed separating “preclinical obesity” (excess fat with organs still working normally) from “clinical obesity” (excess fat that is already affecting organ function or daily life), to help decide who needs treatment most urgently. Body mass index (BMI) is weight in kilograms divided by height in metres squared. It is a screening tool, not a diagnosis on its own.

Obesity has more than doubled worldwide since 1990. According to the WHO, in 2022 about 1 in 8 people in the world was living with obesity. It is common in the Gulf region, and in Saudi Arabia surveys have found that around a fifth to a third of adults are in the obesity range, depending on the survey and the year; the exact figure should be checked against the latest Ministry of Health survey.

Weight is regulated by the brain, which defends a “set point” and increases hunger and lowers energy use after weight loss, so regain is common. Genes explain a large share of who gains weight easily. Environment adds to it: calorie-dense foods and sugary drinks, large portions, little walking in hot weather, long sitting, short sleep, stress, and some medicines (certain antidepressants, antipsychotics, steroids, insulin and others). Medical causes include an underactive thyroid, polycystic ovary syndrome, Cushing’s syndrome and rare genetic conditions. In Arab and South Asian populations the same BMI often carries more body fat, particularly around the abdomen.

Your clinician measures height and weight to calculate BMI, and should also measure waist circumference or waist-to-height ratio, because two people with the same BMI can have very different amounts of belly fat. Standard WHO BMI categories for adults: 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30 to 34.9 class 1 obesity, 35 to 39.9 class 2, 40 or above class 3. NICE (2025) advises lower BMI cut-offs for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background: overweight from 23 and obesity from 27.5, because health risk begins at lower BMI. For waist, the International Diabetes Federation uses 94 cm or more for men and 80 cm or more for women for Arab populations; a waist-to-height ratio of 0.5 or more (waist at least half of height) suggests increased risk. BMI can mislead in very muscular people, older adults with muscle loss, and during pregnancy. Then the important step is to look for related conditions: blood pressure, blood sugar (HbA1c), cholesterol and triglycerides, liver tests with a liver scan or elastography, sleep apnoea screening, thyroid and other tests as needed, and screening for depression and disordered eating.

Obesity is manageable but usually lifelong, like high blood pressure or diabetes: when treatment stops, weight tends to return. The best results come from a long-term plan with regular follow-up. Even modest, sustained weight loss lowers the chance of type 2 diabetes, helps fatty liver and joints, improves mood and sleep, and can reduce the number of medicines needed. Setbacks and regain are part of the condition, not personal failure.