Meat, seafood, eggs, milk, nuts, legumes and high water content plant foods (fruits and vegetables) are a generally good dietary sources of Lithium. Fats, grain-based and sugary foods are poor sources. If you're not lucky enough to live in an area with a high Lithium water supply, a low calorie density paleo-type or plant-based diet is probably the best way to ensure an optimal Lithium intake.

(Tomatoes are a particularly good source IIRC).