What is obesity? Why doctors now call it a chronic disease

For a long time, obesity was seen as a matter of willpower: eat less, move more, and the problem is solved. We now know that this is far too simple. Obesity is a long-term, relapsing condition shaped by genes, hormones, the brain’s appetite centres, sleep, stress, medicines and the food environment around us. Understanding it this way helps people get proper care instead of blame.

What exactly is obesity?

Obesity means having excess body fat that affects, or is likely to affect, health. The important word is fat, not weight. Two people can weigh the same, but one may carry more muscle and the other more fat. Where the fat sits matters too. Fat packed around the liver, gut and heart (visceral fat) is far more harmful than fat under the skin of the hips and thighs.

Excess fat is not just stored energy. Fat tissue releases hormones and inflammatory signals that drive insulin resistance, raise blood pressure, upset cholesterol and strain the liver, heart, kidneys and joints.

Why do doctors call it a chronic disease?

Like diabetes or high blood pressure, obesity:

• develops over years and rarely goes away on its own
• has biological causes, including strong genetic and brain-driven appetite effects
• tends to come back when treatment stops, because the body defends its highest weight by increasing hunger and slowing energy use
• causes or worsens many other diseases

Calling it a disease is not about labelling people. It is about recognising that people with obesity deserve the same evidence-based care as people with any other long-term condition, without stigma.

Why are Indians at risk at a lower weight?

Indians, and South Asians in general, tend to have more body fat, more belly fat and less muscle at the same body mass index (BMI) than people of European origin. This is sometimes called the “thin-fat Indian” pattern. As a result, type 2 diabetes, fatty liver and heart disease appear at lower BMIs and at younger ages in India.

That is why Indian and Asian guidance uses lower cut-offs: overweight from a BMI of 23 and obesity from 25, rather than the 25 and 30 used in Western countries. You can check your own number with the BMI calculator for Indians, and read more in BMI for Indians and the Asian cut-offs.

Is BMI enough to diagnose obesity?

No. BMI is a useful screening number, but it cannot tell fat from muscle or show where fat sits. A muscular athlete may have a “high” BMI, while an older person with thin arms and a large belly may have a “normal” one.

This is why doctors also look at waist size and waist-to-height ratio, which reflect belly fat more directly. Read waist size and health risk and the Body Roundness Index.

What are clinical and preclinical obesity?

In January 2025, a global commission published in The Lancet Diabetes & Endocrinology proposed a new way to think about obesity. It suggested:

• Confirming excess fat properly, using BMI together with at least one other body measure such as waist size, or by measuring body fat directly, rather than relying on BMI alone.
• Clinical obesity: excess fat is already causing problems in the body’s organs or limiting daily activities. Examples include breathlessness, sleep apnoea, knee pain that limits walking, fatty liver damage, heart failure, or high blood sugar and blood pressure linked to excess fat. The commission described this as an illness that needs timely treatment.
• Preclinical obesity: excess fat is present, but organs are still working normally. The risk of future disease is higher, so the focus is on counselling, monitoring and prevention.

An Indian expert group published a similar, India-specific framework in 2025, with a milder stage of increased fat and a more advanced stage with functional limits or related diseases. These frameworks are still being debated and are not yet used the same way by every doctor. They do, however, reflect a shift from “how much do you weigh?” to “is your weight harming your health?”.

What causes obesity?

Usually many things together:

• Genes and family history, which strongly shape appetite and where fat is stored
• The brain’s appetite system, which can drive hunger and cravings
• Diet, particularly refined carbohydrates, fried snacks, sugary drinks and large portions
• Low activity and long sitting hours
• Poor sleep, stress and shift work
• Medicines, such as steroids, some antidepressants and insulin
• Hormone conditions, such as PCOS, an underactive thyroid or, rarely, Cushing’s syndrome

How is obesity treated?

Treatment is long term and personal. It usually combines:

• Nutrition changes that you can sustain, with enough protein
• Physical activity, including resistance exercise to protect muscle
• Sleep and stress care
• Medicines for people who meet medical criteria. Read who should consider weight-loss medicines.
• Bariatric surgery for some people with severe obesity

Even a 5 to 10 percent weight loss can improve sugar, blood pressure, fatty liver and joint pain. For some people with type 2 diabetes, larger weight loss can bring diabetes into remission. Read can diabetes be reversed.

What should you ask your doctor?

• Is my weight affecting my health now, or mainly raising future risk?
• What are my waist size and waist-to-height ratio?
• Should I be tested for diabetes, fatty liver, sleep apnoea or thyroid problems?
• Which treatment options suit me?

An endocrinologist or obesity medicine specialist can help build a long-term plan. Book a consultation.