Recently I've been thinking a lot on why being lean is an ideal nowadays. Some time ago it was a sign of poverty. That's why former rulers let themselves be painted in expensive clothes and with a huge belly. Although pomposity was fashionable back then, I think that someone with a lean and modest appearance would have gained at least equal respect. The underlying cause for my assumption is that living lean is not just trendy, but based on virtue.
The first principle that leads to a lean life is pure pragmatism. The less you have (fat on your body, items in your household, appointments to keep in mind, ...), the more flexible you are. Additional stuff simply is a burden that you need to deal with. You need to carry it around as weight or take care of it in some other sense. In any case it loads you with responsibilities.
As a second reason living lean shows that you know what you need and what you don't. This non-neediness is a goal to strive for and comes along with great freedom. Only when you know yourself well it is possible to refuse a second helping. And it takes the same amount of awareness to not buy that ice crusher for cocktail parties you are never going to throw.
Being lean is not just to look the way society suggests you to in the 21st century. It is an essential part of minimalist philosophy and its foundations are sound.