13.1
Can a vegan diet cover all essential amino acids?
The short answer is: Yes, a healthy vegan diet can cover all essential amino acids if it includes enough protein and complementary protein sources.[188] Alternatively, a variety of plant-based protein sources can be replaced with potato protein, one of the few plant-based protein sources that provides all essential amino acids.
The long answer is: It depends on the plant protein sources.
Since plant-based protein sources vary widely in their content and composition of essential amino acids, some could potentially be critical if a vegan consumes only certain types of plant proteins. The three amino acids showing the highest variation within plant protein sources are lysine, leucine, and methionine.[189]
For instance, vegans who get a high proportion of their protein from cereals may run short of the essential amino acid lysine.[188] However, studies show that consuming enough lysine may not be a problem for most vegans. For instance, in the EPIC-Oxford study[190] vegans consumed an average of 42 mg of lysine per kg of body weight, which is largely higher than the estimated average requirement of 30 mg/kg.[188]
Besides lysine, the essential amino acid leucine may be important for vegan athletes. An optimal intake of leucine (1–3 grams of leucine per meal, especially post-workout)[189] is recommended for optimal performance and recovery[88] because leucine acts as a molecular trigger to stimulate muscle protein synthesis.[191]
Athletes eating a vegan diet can get the recommended leucine intake from their diet if they choose the right plant protein sources for their meals. For instance, 15 grams of corn protein, 25 grams of potato protein, or 29 grams of either pea or soy protein will provide 2 grams of leucine.[189]
Another essential amino acid that vegans should be aware of is methionine. Methionine is typically lower in plant-based proteins (about 1.0%) compared to animal-based proteins (about 2.5%) and thus vegans may not meet their recommended requirements (about 1.6%).[189]
In addition, plant proteins that are high in methionine are often low in lysine, and vice versa. For instance, soy, microalgae, and pea contain little methionine but high amounts of lysine. In contrast, corn, hemp, and brown rice contain high amounts of methionine, but not lysine.[189]
That said, there are two ways to solve this problem: ingest more protein (if you only consume a few sources) or combine different plant protein sources with complementary amino acid profiles. For example, the low lysine or methionine content of corn, hemp, brown rice, soy, and pea protein can be overcome by eating two to four times more protein. Alternatively, combining corn, hemp, or brown rice (low in lysine but high in methionine) with soy, microalgae, or pea (high in lysine but low in methionine) will result in a more ‘complete’ amino acid profile.[189]
However, there is one plant-based protein source that can meet all essential amino acid requirements and may even be better than some animal proteins — the humble potato.
That may surprise you, but potatoes are a true all-rounder when it comes to protein. In fact, the essential amino acid content of potato protein (37%) is higher than egg (32%) and casein (34%).[189] Also, potato protein provides more lysine (8.3%) than egg (7.0%) and casein (8.3%).[189] And even though potato is high in lysine, it is one of the few plant-based sources that also provides sufficient amounts of methionine (1.6%).[189] Overall, 30 grams of pure potato protein contains as many essential amino acids as 25 grams of pure whey protein.[189]
However, one drawback with using potatoes as a protein source is, ironically, their low protein content. Depending on the preparation method, the protein content of most potato varieties ranges from 1 to 4%.[192] Thus, to obtain 30 grams of pure protein, one would have to eat 750–3,000 grams of potatoes.
That said, an attractive alternative to raw potatoes is potato protein isolate, which contains up to 80% protein.[189] Thus, a protein shake containing approximately 38 grams of potato protein isolate delivers 30 grams of high-quality plant protein alongside sufficient amounts of all essential amino acids.
To conclude, a well-balanced vegan diet can provide all essential amino acids. To make sure that a diet includes sufficient amounts of lysine and methionine (for the average person) and BCAAs such as leucine (for the vegan athlete), a variety of plant-based protein sources should be consumed. Alternatively, potato protein can also provide all essential amino acids, though eating a variety of different sources is nevertheless recommended to meet other nutrient requirements, such as vitamins and minerals.
However, this raises yet another question: If plant protein can provide all the essential amino acids, why is animal protein still considered to be superior in terms of overall protein quality?