Phenylalanine is an amino acid which are the building blocks of protein. It is considered essential because your body cannot manufacture it; therefore it is a dietary necessity. Your body converts phenylalanine to tyrosine, another amino acid needed to make protein and thyroid hormones. It is also needed to make dopamine, norepinephrine and epinephrine, brain chemicals that influence energy and mental health.
Despite their small size, eggs, particularly the whites, are one of the richest sources of phenylalanine. A 3.5 oz. portion of egg whites contains more than 5,000 mg of phenylalanine. One whole 3.5-oz. egg contains half that amount, at 2,500 mg.
Nuts and Seeds
Seeds, particularly cottonseeds, sesame seeds, sunflower seeds and flours made from these seeds, are phenylalanine-rich. Cottonseed flower contains more than 3,000 mg of phenylalanine per 3.5 oz. portion, sesame seed flour contains 2,500 mg and sunflower seed flour contains 2.46 mg, while peanuts contain 1,400 mg per 3.5-oz. serving.
Meat and Fish
Protein-rich meats -- beef, pork, turkey, lamb and chicken -- as well as Alaskan native whitefish and Pacific cod contain significant amounts of phenylalanine. The amount varies from about 1,000 to 2,000 mg per 3.5-oz. portion.
Animal-derived products are generally protein-rich, so dairy products such as milk, cheese and cottage cheese contain high amounts of phenylalanine. For instance, whole milk contains almost 4,000 mg of phenylalanine in a 6-oz. glass, while a 3.5-oz. portion of Parmesan cheese contains over 2,000 mg of phenylalanine.
For vegetarians and vegans seeking dietary phenylalanine, soy is an option. It is a major source of phenylalanine; with over 4,500 mg of phenylalanine per 100 g, it contains more than the same portion of most meats.
Non-nutritive sources of very small amounts of phenylalanine include artificial sweeteners, such as aspartame, a sweetener used commonly in diet sodas.