Plant protein
Protein from pulses, cereals, nuts and seeds, often low in one essential amino acid when eaten alone, but complementary when combined.
Plant protein comes from pulses, cereals, nuts, seeds and derivatives such as tofu, tempeh or seitan. It differs from animal protein in two ways: its amino acid profile and its digestibility, which is generally a little lower.
The key point is the limiting amino acid. Pulses are low in methionine but rich in lysine; cereals do exactly the opposite. Eaten alone, each source is therefore incomplete, but combined they complement each other perfectly. Rice and lentils, semolina and chickpeas, maize and beans: traditional cuisines found the answer long before biochemistry did.
There is no need to combine them in the same meal. This advice was repeated for a long time and is now outdated: the body has a pool of amino acids and the balance is struck over the course of the day. Eating cereals at lunch and pulses in the evening does the same job.
A few plant sources are exceptions and have a complete profile: soya and its derivatives, quinoa and buckwheat. The real point of vigilance on an exclusively plant-based diet is not protein, which is widely available, but vitamin B12, which is absent from the plant kingdom and needs to be supplemented.