Move away from the 'brands' Any supermarket has a wealth of fresh produce, fish, meat and cheese, yoghurts (brasse are like greek yoghurt, just check to see if it is non sweetened; ie sans sucre ajouté, vegetables; just avoid the patisserie section. The markets are also good;though sometimes expensive. There are fewer ready made products since most French people (perhaps outside the big cities) don't eat them.
Breakfast cereals in France are very high sugar, probably more so than the UK. They are (sadly) aimed at children. The traditional breakfast of bread dipped in coffee or chocolate (or indeed croissants )is probably also not for you a good idea. But as long as you aren't in a hotel, there are plenty of protein alternatives in the supermarket.(not shakes, things like ham, cheese, eggs, avocados, smoked fish
If you eat bread avoid baguettes (french sticks) and choose pain de campagne (made with less processed flour and sourdough) or pain de noix (walnut bread)
