Obesity, a chronic disease and a global epidemic

A global epidemic, a chronic disease

The World Health Organization (WHO) speaks of a global obesity epidemic¹. It is a major public health issue that goes far beyond individual behaviour. Obesity is a chronic disease with many causes. Its care is long term, with support adapted to your health, your needs and your daily life.

The 2026 Swiss guidelines describe it as a chronic, relapsing and multifactorial disease, characterised by excess body fat that harms health. In Switzerland, about 43% of adults are overweight or living with obesity, including 12% with a BMI of 30 or more².

In 2025, an international commission proposed distinguishing “preclinical” obesity, with no current organ damage, from “clinical” obesity, with organ damage or limitations in daily activities³. This proposal is a reminder that BMI alone cannot tell whether a person is ill: see Understanding your BMI and looking beyond the number.

Why does lost weight tend to come back?

It is not simply a question of willpower.

After weight loss, the body defends itself: the hormones that regulate appetite remain altered and hunger stays stronger, sometimes for a long time⁴. So the body pushes you to regain the weight you have lost. Likewise, when an obesity medicine is stopped, part of the weight lost is usually regained⁵, and partial regain remains possible years after an operation.

This is typical of a chronic disease, which is treated over the long term, like high blood pressure. See Weight regain after treatment or surgery.

Many causes

Obesity almost always results from several factors adding up: inherited predisposition, environment and lifestyle, sleep, mental health, certain medicines, hormonal changes, stress and living conditions². See Causes of obesity.

Possible consequences for health

Obesity can be accompanied by complications affecting in particular the heart and metabolism, breathing during sleep, the liver, the joints and mood². Not everyone develops them; they are checked for during the assessment. See Obesity: associated diseases and health consequences.

What this means for you

• It is not your fault. The Swiss guidelines point out that stigma causes harm and hinders access to care².
• Treatment combines several approaches, which may change over time: medical follow-up, nutrition, psychological support, physical activity, medicines and, in some situations, surgery.
• The goals go beyond the number on the scales: your health, how comfortable you feel in daily life and your well-being².
• Regular follow-up is useful, with at least one review a year with your GP (family doctor)².

When to seek a specialist opinion: see When should you see a specialist?

Frequently asked questions

If it is a disease, do my efforts make any difference?

Yes. Diet, physical activity, sleep and psychological support remain the foundation of all treatments, including with a medicine or after an operation². These efforts are simply not always enough, and that is not a personal failure.

What next?

A first consultation is an opportunity to review your situation and ask your questions. Possible treatments are then discussed with you. Your request is received by the Centre’s appointments team, who will organise the next steps with you.

Medical review of the French version: Dr Pierre Fournier

Scientific sources and references

Sources accessed on 15 October 2026. Reimbursement rules and information on medicines change over time.

1. World Health Organization. Obesity: preventing and managing the global epidemic. Report of a WHO consultation. WHO Technical Report Series 894. Geneva: WHO, 2000. View source
2. Gerber PA, Collet TH, Favre L, et al. Swiss obesity clinical practice guidance. Swiss Med Wkly. 2026;156:5415. View source
3. Rubino F, Cummings DE, Eckel RH, et al. Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 2025;13(3):221-262. View source
4. Sumithran P, Prendergast LA, Delbridge E, et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011;365(17):1597-1604. View source
5. Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553-1564. View source