“If you are a vegetarian, you’re at a greater risk of developing tryptophan malnutrition. Even if you never touch a piece of meat, you do get some tryptophan from foods like nutritional yeast, milk products, nuts, seeds, bananas, and pumpkin. But other than the milk products and yeast (which many vegetarians don’t eat), most vegetarian foods contain much less tryptophan than animal-derived foods do. And that’s important to remember, because decreases in the amount of tryptophan you consume can so easily prevent your brain’s serotonin stores from increasing.”