Discussion: why it is easy to gain weight in the Netherlands?

I have been in the netherlands for almost two years.  I have gained some weight, although the situation is not very severe. But my brother, who used to be very thin, became a BIG GUY during his stay here. Moreover, some of my friends are also concerned about their weight. I am wondering why it is easy to gain weight in the Netherlands? Is there some way to avoid such process?

For example ,on a diet? Which ,it is said,never once gat fucking succeed...

Anyway,hope you good luck!