I ran the Jacob van Maerlant Route, unsupported.
First, I would recommend the Jacob van Maerlant Route to everyone. It is a diverse route: you pass small villages such as Lapscheure, Sluis (very charming) and Vivenkapelle. These beautiful villages are connected with calm roads surrounded by nature and the roads parallel with the Leopold Canal and Canal Damme-Zuid. The 'do it yourself' ferry of Kobus (Lapscheure) is also fun!
Starting at the Market Square of Damme, I ran North to Sluis while passing the Belgian-Dutch boarder. The first 30 km went great. I kept a nice pace and my body felt good. Unfortunately, I met the infamous "sugar dip". At first, I fought against it, but I discovered quickly my energy dropped meter by meter. Back on Belgian soil (approximately around km 38), I thought about quitting. I tried many options: taking small breaks and got back to running, walked a bit in between running etc. Around km 45; the best (or less worse) solution was running 1 km, walking the next km and repeating that until the end. Luckily, at km 53 I saw the church of Damme and tried to move my feet in a faster pace until I got back at the Market Square of Damme at km 55!