No, not all plants contain all the indispensable (essential) amino acids required for a complete diet. While most plants provide some amino acids, very few individual plant sources contain all nine essential amino acids in sufficient quantities. These amino acids are crucial because the human body cannot synthesize them, so they must come from the diet.

The main exceptions in the plant world are quinoa, soybeans, buckwheat, chia seeds, and a few others, which are considered “complete” proteins because they contain all essential amino acids in adequate amounts. However, most other plant sources (such as grains, beans, nuts, and seeds) are lower in one or more essential amino acids, often lysine or methionine.

For those on plant-based diets, this isn’t a major issue as long as they consume a variety of protein sources. By eating complementary proteins — for example, grains (low in lysine but high in methionine) and legumes (high in lysine but low in methionine) — people can obtain all essential amino acids over the course of the day, even if not in a single meal. This approach allows for a nutritionally complete amino acid profile in a plant-based diet.