Many protein powders are plant-based, and depending upon the plants used to make them, they may be complete or incomplete proteins.
The American Dietetic Association states that while food supplements can help people meet their daily nutrition goals, incorporating a diet with a wide variety of nutrients rich in protein is usually the right strategy for meeting daily requirements.
Read the labels though! Some protein supplements can be high in sugar or sodium to improve their taste.
Plant vs. animal protein
According to the Dietary Reference Intakes (DRI) in use by Health Canada, healthy women need 46 grams of protein per day, men need 56 grams, children aged 1-3 require 13 grams, and children aged 4-8 need 19 grams per day. Pregnant and breastfeeding women, of course, need more (71 grams from the second half of pregnancy).
Although the human body creates 11 amino acids, it requires a further 9 from food. Some plant products, such as soya beans and quinoa, are also complete proteins, but most others are not. This means a person following a vegan or vegetarian diet should be eating a varied diet of plant-based foods to get the required range of amino acids. This would include high-protein foods such as tofu, tempeh, lentils, nuts, seeds, and quinoa.