That doesn't have much baring as although the UK is a tubby country by European standards, the Greek women are still fatter and they have less money.

The Germans have a hell of a lot of money, as do the Swiss and Austrians, and all that chocolate to boot, but they are only a little bit chubby countries.

IMO it has a lot to do with acceptability, how much crap you get for being overweight, the allowances made within your society for your weight. If you are properly obese in Italy, expect to have it pointed out to you on a daily basis. In Spain it's bloody hard to find clothes for big women, and recently Zara (Spannish clothes chain) started to make larger clothes for the UK market, stating that British women needed catering for especially.

'All you can eat' is still a very strange concept to many Brits. If there is a set price for unlimited food it would be more commonly found in the form of a buffet, and then it would be advertised as a buffet, not 'all you can eat'.
Pizza Hut do an 'all you can eat' lunch, and people get in trouble for trying to share the food out to be cheap, there's the attraction, not in eating loads.

You can guess what many French people think of 'all you can eat'....

The emphsis is generally on quality, not quantity, which is probably why American chocolate tastes rather like highly flammable fatty sugar and cocoa, compared to Belgian and Swiss freakin' perfection.