Nature gives a boost or penalty to a Combat Statistic when Leveling Up.
The boost is +10% and the penalty is -10%.

In addition, it also gives an XP boost or penalty when a certain category of foods/meals is consumed.
The boost is +100% XP and the penalty is -50% XP.

There are 25 Natures total. Five of them make an Animu indifferent, and they get neither a bonus nor a penalty.