Obesity: Reading the Whole Picture, Not Just the Weight

One number is not enough

A body mass index (BMI; weight divided by height squared) of 30 or above falls into the obesity range. But BMI is limited on its own: it cannot tell fat from muscle, and it does not show where fat is stored. It can overestimate fat in athletes and underestimate it in older adults; in Asian populations, risk begins at a lower BMI.

That is why simple measures such as waist circumference, waist-to-hip ratio and waist-to-height ratio come into play. A waist above 102 cm in men or 88 cm in women is in the obesity range, and a waist-to-height ratio above 0.5 points to central (abdominal) fat. When needed, fat can be measured directly, for example with DEXA (dual-energy X-ray absorptiometry). The 2025 Lancet Commission likewise suggests confirming excess body fat with a measure beyond BMI.

There is no single culprit

Obesity is not simply a matter of 'eat less, move more'. Beyond energy balance, genetics (heritability of 30–50%), sleep, gut microbiota, medications, quitting smoking and the environment all play a part. About 30% of adults and 69% of adolescents do not sleep enough. The presentation’s central message: obesity is not a failure of willpower but a chronic disease that needs lifelong management.

What matters is not only how much fat there is, but where it sits (inside the abdomen, in the liver and muscle) and how it behaves. This view is captured by the term 'adiposity-based chronic disease', which puts the disease mechanism ahead of a stigmatizing word. The presentation also recommends saying 'person with obesity' rather than 'obese patient', because a health worker’s bias can lower the quality of care.

The consequences are wide-ranging: type 2 diabetes, cardiovascular disease, several cancers, sleep apnea, gallstones and depression among them; even a gain of 4.5–5.5 kg raises the risk. There is also a vicious circle: knee pain, depression and sleep apnea make movement and sleep harder.

Lifestyle: a modest start, essential maintenance

According to the presentation, there is no ideal diet, only a sustainable energy deficit. At equal energy intake, the macronutrient mix (the split of carbohydrate, fat and protein) does not change weight loss. Plant-focused, minimally processed eating with low energy density stands out. Goals should be realistic: losing 3–5% of body weight can improve cardiovascular markers, and 5–10% brings more benefit. Expectations are often higher, so this is worth discussing at the very start.

With exercise, the dose matters. Its effect on weight loss is modest, but keeping weight off takes 200–300 minutes a week of moderate-to-vigorous activity; at that level, a 16.8% loss was maintained over 24 months. Resistance exercise helps preserve lean mass and strength. Responses also differ from person to person: the same exercise produced losses anywhere from 3 to 12 kg, a reminder of the role of biology.

Small steps count too. Short bouts (under 10 minutes) matter, though bouts of 10 minutes or more are more closely linked to weight loss. Sleep matters too: after 5 days of restricted sleep, energy intake rose and sweets consumption went up 52%.

Medication and surgery: beside lifestyle, not instead of it

GLP-1 (glucagon-like peptide-1)-based medicines have changed obesity treatment. In the presentation they are always mentioned as an addition to lifestyle treatment, and are considered at a BMI of 30 or above, or 27 or above with a weight-related disease. In one study, two-thirds of the weight had been regained one year after stopping the drug, a reminder of the chronic nature of obesity. Nausea, vomiting, constipation and loss of lean mass are topics to raise with a physician. Medication decisions are made together with a physician.

Bariatric (metabolic) surgery is described as the most effective treatment, yet it is a tool, not a cure. Current guidance allows it to be considered at a BMI of 35 or above without requiring another disease. After surgery, lifelong follow-up is needed for vitamin and mineral deficiencies, digestive problems and mental health; weight regain of 20–35% is reported. The decision on surgery is also made together with a physician.

Do not forget the liver

In obesity, fat can also collect in the liver, so MASLD (metabolic dysfunction-associated steatotic liver disease: fatty liver together with at least one cardiometabolic risk factor) should come to mind. The presentation links weight loss of 5%, 7% and 10% to less liver fat, regression of MASH (fatty liver with inflammation) and regression of fibrosis (scarring) respectively. The foundation is still lifestyle: Mediterranean-style, plant-focused eating, exercise and no alcohol, since no alcohol level is considered safe.