There are tons of articles and YouTube videos about this, so am just going to mention a few. These are often mentioned and having looked into it a bit more I think these may actually work.

1. Oatmeal

2. Avocados

3. Eggs

4. Broccoli

5. Sprouts

6. Tuna and other fish

7. Pomegranates and unsweetened pomegranate juice

8. Olive oil