The most likely answer is that there are enough people foolish enough to pay that much for water. As the old joke goes, "Evian" is naive spelled backwards.

As for the cost of fats verses other, more healthy foods, what are the costs of production and distribution for vegatables compared to meat? Meat can be frozen and usually has a longer shelf life than fresh vegatables, so that could be a factor in their higher price. Distribution costs could be a major factor. Here in Colorado, a high percentage of our fresh produce must be shipped in from other states and even other countries in the winter while a lot of livestock is raised here.

As a general rule, countries with a heavily regulated economy tend to have less of everything available to the public, so it isn't surprising that they tend to have lower obesity rates. Governments with heavily regulated economies often regulate the price of staples, but that tends to reduce production of those same staples.

Capitalism has sparked advances in agriculture has greatly reduced the cost of food over the past 100 years as well as the number of people necessary to produce the food. Improved nutrition due to the wider availability of food is a major factor why each successive generation over that time was taller than their parents. It may well also be the reason why the age of menarche has been declining over much of the same time period.