Well...I used to think that they were healthy...but now that I have done some researches, I will say that it also depends if you buy them at the supermarket or if you make them yourself at home!!
Did you know that most of the muesli bars available in the supermarkets contain more than 18% is sugar? Some contain up to 31% of sugar! And sometimes the sugar doesn't even come from natural dried fruits but simply added refined sugar.
Today, I bake some muesli bars so that I know what is inside! As I calculated the nutrition ingredient panel, I realised that they still contain lots of sugar (15%) but at least I know that the ingredients are natural and the muesli bars healthier than the ones you can find on the supermarkets (no thickeners, no additives, no refined sugars such as brown sugar or juice concentrate...)!
But as they provide lots of energy, I will keep them as a healthy treat :)