What it is
Leucine 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, leucine must be consumed from dietary sources.
For more on the general effects of protein, refer to the article on protein.
The recommended intake of leucine is 56mg per kilogram of body mass.
Likelihood of tracking completeness: Very low
Leucine is not a nutrient food manufacturers are required to disclose on nutrition labels. The vast majority of food manufacturers do not voluntarily list leucine content on nutrition labels, so most branded products in the MacroFactor database lack information on leucine. So, if you’d like to accurately track your leucine 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 leucine to be the limiting amino acid, so insufficient leucine intake is rare, from the perspective of general health and well-being.
Leucine is heavily implicated in initiating muscle protein synthesis, so foods that are high in leucine are thought to be especially important for building muscle. Animal proteins are generally higher in leucine than plant proteins, so some vegans may struggle to consume enough leucine to maximize muscle growth. However, most vegans who aim to maximize muscle growth also consume plenty of soy-based products, since so many soy-based foods have high overall protein content. Soy protein is particularly rich in leucine, so obtaining adequate leucine intake to maximize muscle growth isn’t a problem for most vegans (though it may be an issue for vegans who eschew soy-based protein sources).
For more on nutrients with a greater likelihood of insufficient or excessive intake, you should check out this article.
Signs of deficiency/insufficiency
The most common signs of a leucine deficiency are a loss of appetite and muscle wasting.
Omnivores and vegetarians rarely need to worry about consuming adequate leucine, 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, dried seaweed (nori), watercress, almond-based vegan cheeses, and wheat gluten are excellent sources of leucine per unit of energy.
If you’d like to learn more about micronutrients generally, there’s a five-part series on the MacroFactor website you might enjoy.