Food for thought
Definition 1 of 1
Pro Tip 1/3Reflection Prompt
Used when you hear or see something that challenges your thinking or inspires deeper consideration. 
His speech on climate change gave us some real food for thought.
Pro Tip 2/3Not Literal
It doesn't mean actual food, but rather ideas or information for your mind to 'digest'. 
The documentary offered plenty of food for thought about our dietary habits.
Pro Tip 3/3Conversation Starter
Often used to introduce thoughts or opinions that could spark a deep conversation. 
Her proposal on renewable energy policies is good food for thought.