Very simple suggestion this time (as i've run a game with Nutrition active for change) :
Add a Nutritionist book in game that learn you the skill (as "The Herbalist" or "How to branch a generator" magazine).
Also add to the description of this item some sentence like the following line : "Learn to know food values and how to reach the 1500 cal./day* you need to stay in shape."
* : it take me some research to exhume the 1500 cal. info (actually from a msg in Steam forum) that allow me to keep my characater near a stable weight... So, yes, it matters to know that particular info IG to stop gain/loss of weight.
I'm still not sure you need to keep geting 1500 cal a day, but you indeed need to go for that amount at some point to reach the stable state on weight balance (in PZ world)...