Yes, that's an interesting and important point brought up by the study! Even though a well-balanced vegan diet can provide adequate protein, there may still be concerns about certain essential amino acids that might not be as abundant or bioavailable as those found in animal-based protein sources. Essential amino acids are those that the body cannot produce on its own, so they must come from the diet.

Some studies suggest that while plant-based proteins like beans, lentils, quinoa, and soy provide a broad range of amino acids, they may still fall short in certain key amino acids like methionine or lysine. However, the solution typically involves consuming a variety of plant-based protein sources to ensure that you’re getting all of the essential amino acids. For instance, combining grains (which might be low in lysine) with legumes (which provide lysine but can be lower in methionine) can help to make sure you're covering your amino acid needs.

It's also worth mentioning that while plant proteins might require more variety to achieve a complete amino acid profile, many vegans can still meet their protein needs with careful planning. Have you been following a vegan or plant-based diet, or are you exploring it?