What it is
Phenylalanine is an essential amino acid.
What it does
Amino acids are the building blocks of proteins. You don’t really need to think about what each amino acid does – your body just needs enough of each amino acid to build the proteins it needs to build.
Nonessential amino acids are amino acids your body can synthesize from other raw materials. You don’t need to consume nonessential amino acids in your diet, but most normal diets will contain plenty of nonessential amino acids.
Essential amino acids are amino acids your body can’t synthesize from other raw materials. So, you do need to consume essential amino acids in your diet.
Conditionally essential amino acids are amino acids your body can generally synthesize under most circumstances, though there are instances where it may not be able to (due to infancy, advanced age, liver disease, or certain other disease states).
As an essential amino acid, phenylalanine must be consumed from dietary sources.
For more on the general effects of protein, refer to the article on protein.
Recommended intake
The recommended combined intake of phenylalanine and tyrosine is 44mg per kilogram of body mass. A normal diet generally has a ~55/45 split of phenylalanine and tyrosine, so we set the target for phenylalanine at 24.2mg per kilogram of body mass.
Likelihood of tracking completeness: Very low
Phenylalanine is not a nutrient food manufacturers are required to disclose on nutrition labels. The vast majority of food manufacturers do not voluntarily list phenylalanine content on nutrition labels, so most branded products in the MacroFactor database lack information on phenylalanine. So, if you’d like to accurately track your phenylalanine intake, you’ll need to make a point of mostly tracking “common foods,” which come from research-grade databases that have full nutrient reporting.
For more on when you can track using branded foods versus common foods when you’re trying to accurately monitor your intake of particular nutrients, you should check out this article.
Likelihood of insufficient intake: Low
Insufficient intake of a single essential amino acid can have health consequences. The essential amino acid with the lowest intake relative to physiological needs is referred to as the limiting amino acid. The four most common limiting amino acids are lysine, methionine, threonine, and tryptophan. Lysine or threonine is likely to be the limiting amino acid for individuals who consume most of their total energy from cereal grains (like rice and wheat). Methionine is likely to be the limiting amino acid for individuals who consume most of their total energy from legumes (like beans, chickpeas, and lentils). Tryptophan is likely to be the limiting amino acid for individuals who consume most of their total energy from corn/maize.
It’s very uncommon for phenylalanine to be the limiting amino acid, so insufficient phenylalanine intake is rare.
For more on nutrients with a greater likelihood of insufficient or excessive intake, you should check out this article.
Signs of deficiency/insufficiency
Individuals with a condition called phenylketonuria (PKU) lack the ability to properly metabolize phenylalanine, so they have to consume a diet very low in phenylalanine to avoid neurological damage. Osteopenia (weak bones) seems to be more common in individuals with PKU than the general population, but it’s hard to say whether that effect is actually driven by low phenylalanine intake, or whether it’s due to some other confounding factor.
Good sources
Omnivores and vegetarians rarely need to worry about consuming adequate phenylalanine, assuming their total protein intake is sufficient. Meat, eggs, and dairy products are generally rich in all of the essential and conditionally essential amino acids.
Among vegan sources of protein, soy-based products, watercress, wheat gluten, dried seaweed (nori), spirulina, and mycoprotein (like Quorn) are excellent sources of phenylalanine per unit of energy.
Learn more
If you’d like to learn more about micronutrients generally, there’s a five-part series on the MacroFactor website you might enjoy.