Obesity is often described as a simple problem of eating too much and moving too little. The evidence tells a more complex story.
Body weight is influenced by biology, genetics, medicines, mental health, sleep, environment, access to food and many other factors. After weight loss, the body may respond by increasing hunger and reducing energy expenditure, making long-term maintenance difficult. This is one reason obesity is increasingly treated as a chronic, relapsing condition rather than a failure of motivation or willpower.
Effective treatment exists. However, no single approach is right for everyone, and success should not be measured by weight alone.
Obesity is more than a BMI
Body mass index, or BMI, compares weight with height. It is inexpensive and useful for screening large populations, but it cannot directly measure body fat, show where fat is stored or determine how excess body fat is affecting an individual’s health.
A recent international expert commission proposed assessing obesity through two connected components: evidence of excess body fat and evidence of related health problems or limitations in daily functioning.
This means that two people with the same BMI may have different health needs. Clinical assessment may include waist measurements, metabolic risk factors, physical function, psychological wellbeing and obesity-related or associated conditions such as type 2 diabetes, cardiovascular disease, obstructive sleep apnoea, gastro-oesophageal reflux disease, osteoarthritis, depression and anxiety. The person’s symptoms, daily functioning and treatment priorities also matter.
The useful distinction: BMI remains useful, but it should not be the entire diagnosis.
Lifestyle support matters — but “try harder” is not treatment
Nutrition, physical activity, sleep and behavioural support are important parts of obesity care. Their benefits can extend beyond the number on the scale.
In the Diabetes Prevention Program, a structured lifestyle intervention reduced the relative risk of developing type 2 diabetes by 58% over approximately three years among adults at high risk. This was an intensive programme with defined goals and ongoing support, not simply brief advice to lose weight.
Intensive weight management can also produce diabetes remission in selected people. In the DiRECT trial, conducted through primary care practices in the United Kingdom, 46% of participants receiving the intervention reached remission of type 2 diabetes at one year, compared with 4% receiving usual care.
Lifestyle care should therefore be specific, supportive and adapted to the person’s circumstances. It should not be used to blame people when biology, health conditions, medication effects, cost or environment make weight management difficult.
What can newer medicines achieve?
Anti-obesity medicines can help regulate appetite, food intake and other biological processes involved in body weight. Semaglutide and tirzepatide are among the newer treatments authorised in the European Union for chronic weight management in eligible adults, alongside dietary and physical-activity support.
Mean change with semaglutide 2.4 mg, compared with −2.4% with placebo. Both groups received lifestyle support.
Mean change across tirzepatide doses, compared with −3.1% with placebo.
These figures are group averages, not promises. Some participants lost more, some lost less and some stopped treatment. Results from separate trials should not be treated as a direct ranking because populations, methods and treatment conditions can differ.
A direct head-to-head trial, SURMOUNT-5, subsequently found greater average weight reduction with tirzepatide than with semaglutide over 72 weeks in adults with obesity who did not have diabetes. Even so, weight change is only one part of treatment selection. Safety, health conditions, treatment goals, personal preference, availability and cost also matter.
Benefits can extend beyond weight loss
The strongest evidence does not ask only, “How many kilograms were lost?” It also examines whether treatment improves how people feel, function and live.
In SELECT, cardiovascular death, non-fatal heart attack or non-fatal stroke occurred in 6.5% of participants receiving semaglutide and 8.0% receiving placebo. Participants had established cardiovascular disease and overweight or obesity, without diabetes.
This result is clinically important, but it applies to the specific high-risk population studied. It should not be presented as proof that the same cardiovascular benefit exists for everyone using semaglutide.
In the SURMOUNT-OSA trials, tirzepatide reduced the severity of obstructive sleep apnoea and body weight in adults with obesity and moderate-to-severe sleep apnoea. Weight reduction may also improve gastro-oesophageal reflux symptoms in some people.
Obesity care should also consider depression, anxiety, binge-eating symptoms and weight stigma. These relationships are complex and often bidirectional. Weight management does not replace psychological care, treatment for eating disorders or condition-specific treatment for sleep apnoea or reflux disease.
Medicines are effective, but they are not risk-free
The most common adverse effects of semaglutide and tirzepatide are gastrointestinal, including nausea, vomiting, diarrhoea, constipation and abdominal discomfort. Some participants discontinue treatment because of adverse effects.
Safe prescribing requires assessment of medical history, other medicines, contraindications and product-specific warnings. Pregnancy, dehydration, gallbladder or pancreatic concerns, diabetes treatment and planned procedures requiring anaesthesia may require particular attention.
Authorisation is not access: European authorisation does not guarantee that a medicine is reimbursed, locally available or appropriate for a particular person. Current regulatory information and local clinical guidance should always be checked.
What happens when treatment stops?
Weight regain after treatment ends is common. In an extension of STEP 1, participants regained approximately two-thirds of the weight they had previously lost during the year after semaglutide and lifestyle support were withdrawn.
This does not mean that every person will regain the same amount or that one medicine must be continued for life. It does show that obesity often requires a long-term maintenance strategy.
That strategy may involve continued medication, behavioural and nutritional support, a different treatment or a carefully monitored combination of approaches.
Where does metabolic surgery fit?
Metabolic and bariatric surgery is an evidence-based treatment, not a personal failure or an “easy way out.”
International guidance recommends surgery for many people with a BMI of 35 kg/m² or above and recommends considering it at lower BMI levels when metabolic disease is present. Actual eligibility and access vary between health systems.
For appropriately selected people, surgery can produce substantial and durable benefits. Long-term observational evidence has associated bariatric surgery with lower overall mortality and longer life expectancy compared with usual obesity care.
Surgery also carries short- and long-term risks. It requires informed consent, multidisciplinary assessment, nutritional monitoring and lifelong follow-up.
The central message
There is no universally best obesity treatment.
Good care considers the person’s health complications, function, goals, previous treatment response, safety, preferences and access to care. Behavioural support, medication and surgery are not competing moral choices. They are different tools that may be used alone, sequentially or together.
The evidence supports treating obesity with the same combination of scientific rigour, shared decision-making and compassion expected for other chronic health conditions.