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Hello, David here with a new mini-series from the briefing room.

We're packaging up some bits you may have heard before on other programmes,

which are still very relevant,

so they can explain specific things that are going on in the world.

In today's briefing room explainer, weight loss drugs,

let's find out what these new drugs are and what they do. Here with me is John Wilding,

Professor of Medicine at the University of Liverpool. John Wilding, how do we define obese in this

country and what proportion of people are obese? And maybe then you can tell us how that's changed.

Obesity is a complex disease that's associated with an excess amount of body fat.

We've tended to use body mass index, which is your weight in kilograms divided by your height squared in meters.

And a body mass index above 30 is generally considered

to define obesity, although that has its limitations because it doesn't tell us about body fat.

In this country, if we look at that metric, about just under 30% of people will be living

with obesity and about another 20 to 30% will be

overweight, which would be defined as a body mass index above 25. John, I take it just as there's a

difference between being overweight and obese. There's a difference between being obese

and being severely obese. Yes, that's right. In fact, the WHO gives classification.

So a class 1 obesity, the lowest would be between a body mass index of 30 and 35,

class 2 between 35 and 40, and above 40 would be class 3,

or what we would generally call severe obesity,

which is very, very commonly associated with

...