Complete ‘main meal’ diets don’t need any supplements to give your cat all the nutrients they need, but some foods, like treats, snacks and some purely meat/fish-based foods, aren’t nutritionally balanced on their own. Treats or snacks are fine in moderation, but reduce their main meals slightly if you do give them treats to avoid overfeeding! As a rule, no more than 15% of your cat’s daily calories should come from treats.