Let me start by saying, while this question from friends and family is well meaning, it may well be one of the dumbest questions I get asked. Anyone who thinks about this for a few minutes has to realize the answer to this question.
Let's rephrase the question, Where does a cow get its protein? Or where does a horse get its protein? Those answers are self evident. No one has seen a giraffe and thought, poor dear, where do they get their protein.
The answer is simple ... THE
All plant food has protein. As long as you eat a varied amount of plants, don't have some unique disease, and you consume enough calories so you are not starving yourself, you will consume an adequate amount of protein.
How Much Protein Do You Need?
For an in depth explanation of your actual protein requirements and plant based sources of protein read the following linked article.
or for a simpler explanation take 3 minutes and watch this video.
Here is something to think about. When first born human babies have evolved to get everything they need to grow for at least the first 6-12 months of life directly from their mother via human breast milk. These months are our greatest time of growth. I would think that we would need the most protein of our life during this time. So what is the composition of breast milk? Surely it must be very high in protein. While the amount of calories from protein varies calories in human breast milk roughly breakdown as follows:
What this means is that we need far less protein than we have been led to believe. Eating a completely plant based, whole food, no oil, no nuts diet I meticulously tracked my nutrient intake for 6 months. I did have about 1 tbsp of flax seed every day. My breakdown of calories during this time was as follows:
Did I consume enough protein? According to this article the recommended RDA is that 8-10% of your calories should be from protein. I was comfortably over the RDA and if I had consumed any nuts or soy on a regular basis the percentage would have been much higher. Protein hasn't been a nutrient of concern since nutrition scientists corrected their wrong assumptions in the 1970s.
Michael Greger M.D. FACLM June 27th, 2016 Volume 31
Other videos referencing the science of protein on Nutritionfacts
Various Articles on Plant Based Eating and Protein
Disclaimer: The information and advice herein is not intended for use in or as a substitute for the diagnosis or treatment of any health or physical condition or as a substitute for a physician-patient relationship which has been established by an in-person evaluation of a patient. Do not change your diet if you are ill or on medication without the advice of a qualified health care professional such as your physician. In layman's terms, if you are taking any medications switching to a whole food, plant based, no oil diet will require your medications be closely monitored by your physician. And may require some of your medications to be quickly reduced or stopped. Reducing or stopping medications needs to be done under the direct supervision of a physician.