There is a difference between countries like Spain and France, and the UK, and I've lived in all three.
The two former have easier access to a very wide variety of fruit and vegetables. Their lettuces are varied and enormous, for example. The best we have is thr comparatively unappetising little gem. The side salad we would get next to a sandwich in this country is generally seen as a garnish, but abroad its very much part of the meal. In short, our relationship with vegetables is not what it should be, and we have easy access to beige, processed foods that make us lazy chefs.
There is another problem of course, and I think it comes down to housing costs. Houses in the UK are so costly that both partners have to work, where traditionally one partner couls stay at home and prepare healthy meals. This is a very difficult one to unpick, after all, who wants to sell their house for less so that the buyers can work less? Housing in france is much cheaper and pricing is less volatile.
In terms of beer bellies, it is true that beer here usually comes in pints, but in france and Spain a portion is smaller. You do see beer bellies in germany, and they have big glasses there too.
Lastly, as English speakers, we are strongly influenced by American culture, which includes their food, and that's not quite the case in france and Spain.
I am overweight: the cause - my cravings for chocolate bars in pregnancy, and the ease to buy them, though again, the kind of 50g portion snack product isn't really available over there. They do have them, but it's usually a multi pack of four so a bit less of an impulse buy at the newsagents. Their newsagents are also mostly news and mags, rather than chocolate. The range of magazines available in the average town in france is mind boggling, so much more than you could find in the spar here. They are as such exposed to much more inspiration for hobbies. Further, there is massive funding at a local level for grass roots sports of all kinds, think stuff like archery, which is sometimes seen as a bit niche here and is underfunded (I am an archer)