There's a myth that adults don't grow new brain cells, but Sandrine Thuret debunks it and talks about how neurogenesis, the process of making new brain cells, works.
The average adult makes 700 new neurons in their hippocampus every day. These new neurons are important for mood (reduced neurogenesis is linked to depression) as well as learning and memory.
Exercise and learning improve neurogenesis. Also, diet is linked to neurogenesis. If you have a lot of sugar, alcohol, or animal fats, it reduces neurogenesis. Omega 3 fatty acids (eg, flax), a crunchy diet (eg, real foods rather than blended foods), vitamins A, B, and E, and calorie restriction increase neurogenesis.