Increasing any reserve health stamina or mana over it's max will represent weight gain. Does that answer your question?
Eat till your reserves are replenished and not any more, this is why it's generally good to consume isolated nourishment foods with only HN, SN or mana nourishment.
Some prefer have all stats in one food but it's kind of a material waste to do so since cooking is broken.
For example i got health nourishment food, then a stamina nourishment food without HN and mana food. I replenish my reserves and only eat that specific nourishment food.
Then you could not eat at all but you will lose weight over time.