Obesity

BMI is the usual starting point, weight in kilograms divided by height in metres squared. It is a screening tool rather than a diagnosis, because it says nothing about where fat sits or how much of the weight is muscle.

That is why waist measurement is used alongside it. Fat carried around the abdomen carries more metabolic risk than the same amount carried elsewhere, and two people at an identical BMI can have quite different risk profiles.

NICE advises using lower BMI thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds, generally reduced by 2.5 kg/m².

The reason is that metabolic risk appears at a lower BMI in these populations. Someone with a South Asian family background can carry the cardiometabolic risk of a higher BMI while measuring below the standard threshold, so applying a single cut-off across everyone would systematically under-identify risk in exactly the groups where it develops earliest.

It matters practically: it changes who is eligible for treatment, and it is a detail frequently omitted from eligibility information.

Appetite, satiety and fat storage are regulated by hormones. GLP-1, GIP, leptin and ghrelin between them determine how hungry a person feels, how quickly fullness arrives and how long it lasts.

Those signals differ between people, and they adapt when weight is lost: reduced energy expenditure and increased hunger both push back toward the previous weight. That biological response is why weight regain after dieting is the rule rather than the exception, and it is not a failure of effort.

It is also the reason the current generation of treatments works. They act on the same hormonal signals, which is a more accurate description of what they do than "appetite suppressants".

Excess weight raises the risk of a range of conditions, and improvement in those conditions is often a more meaningful treatment goal than the number on the scale.

Dietary and activity change is the foundation of every pathway, and remains part of treatment rather than an alternative to it.

Where that is not sufficient and BMI thresholds are met, licensed medication may be appropriate. These are prescription-only medicines and require clinical assessment; they are used alongside dietary change, not instead of it.

For severe obesity, or where other approaches have not worked, bariatric surgery may be considered. It produces the largest and most durable weight reduction of any current intervention, and carries correspondingly greater risk and permanence.