If the general public ate healthily (as opposed to "junk" food and 2 bottles of diet coke a day), got moderate exercise, and took responsibility for their own health, as opposed to handing that responsibility to the state, then the burden on the NHS would decrease dramatically.
It's many years since I was a pupil in school, so I don't know what they are taught these days, but in my local towns the supermarkets fill up with children at midday buying their lunch, over 90% of which appear to consist of a snack high in sugar and an equally sugary fizzy drink... so what do they know, what habits are they forming, and what will their health be like in 20 years....
But we live in a society where we don't "dictate" to the individual how they should live their lives. They are left at liberty to trash their bodies. Quite why taxpayers are then expected to pick up the burden for caring for people who can't be bothered to care for themselves, indeed could be said to have inflicted their own maladies upon themselves, I don't know......