I’ve read that one of the hardest activities for the body is digesting food. When someone eats something that is hard to digest, then they can become tired, and when one is tired, one can mistakenly think one is depressed. [See related meme below.]
Conversely, the body can quickly digest fruits and vegetables. This has two benefits: the body, and specifically the brain, gets immediate energy, and the body does not waste energy digesting food that is hard to digest.