/ A report on certain Polish eating habits
This is maybe dated and idealized but it gives an idea.
Working days :
breakfast : bread and/or rolls, cold cuts, cheese, maybe tomatoes or jam people don't cook much for breakfast beyond maybe boiled sausage, eggs (scrambled or soft boiled) or the dreaded milk soup (zupa mleczna - rice or some other grain boiled with milk) served with tea and/or coffee
second breakfast : sandwiches eaten at work, more of a snack than a meal
dinner (when everybody's home): usually a soup followed by a meat course with (usually) boiled potatoes and a vegetable dish.
supper : if some member of the family has dinner elsewhere they may have a light supper at home, which is often indistinguishable from breakfast (but no milk soup - hurrah!)
breakfast - like work days but maybe bigger
dinner - early afternoon (like work days but may be more elaborate and require more preparation), one distinctive thing about Polish dinner is that traditionally there's nothing to drink. That was weird for me early on, but I'm used to it now. On special occasions there may be something to drink, esp wine or beer.
supper - in the evening, a lot like breakfast (probably no coffee though), or maybe a one dish meal.
Also dessert isn't eaten directly after the meal. IME cakes are served with coffee sometime between dinner and supper. Typically you eat the cake with the spoon you stir your coffee with.
As to why Polish people are mostly not (Very) fat. I think there are three reasons:
1. activity levels are higher, people walk a lot more
2. portion control (on all except the most festive occasions Polish people typically have one plate, maybe a small second helping and that's it.
3. low levels of between meal snacking. Traditionally Polish people eat three or four meals a day but hardly anything inbetween. The youngest generation is more used to snacking between meals and you see a lot more fat kids than you used to.