I was underweight for most of my life then put on a lot in the middle. It was a continual 'enterprise' to keep my weight down. This year, following my nice little heart attack(s) I lost a few kilos, but two recent visits appear to have tightened my trouser waist again. The irony is that my brother-in-law who will have left the hotel for the long drive home a couple of hours ago has put more on me in three days than my worst eating habits would in three months. I say irony because he is very overweight and has serious health issues but his Algerian origins are a cultural excuse for being 'big'.
I am nonetheless a bit over 78k and need to be under 70k. Having said that, Gordon's point is important. People spend a lifetime underweight as I did and do not look at that as an issue, which having read a bit since then I see is a false impression to be under. Too late now. At the other end of the scale I have things I need to keep an eye on various things in my diet like iodine, vitamin D and fat in particular places rather than just my belly. It is quite hard work.
The time bomb Alexander mentions is something some of my colleagues work on and has been part of a set of issues since a joint WHO/UNICEF/ICCIDD consultation in the mid-1990s. Sugar intake is scary but some of the other aspects of diet are as bad according to what they say. So, yes it seems like a lot of fuss but actually we have to take it seriously.