If I remember correctly, first 2 difficulties you can recover health by meditating more than 1 hour or by eating. Hardest 2 (I am playing second hardest) only be eating. And don't forget you can eat during combat too! I don't mind this system, but for my play style I just end up spamming quen the entire fight and don't get to have fun with the other signs. I think I just need to man up and take some damage to deal more damage though.
This seemed hard and annoying at first, but I like it now and only died a handful of times in White Orchard. I did get the utility regen ability but more for the stamina instead of vitality. I found it pretty annoying in Witcher 2 to have to wait around for my health to slowly regen and then hit F5 for a save before the next fight. Food is a good alternative.