Yes, you can get sufficient protein from whole plant foods.
If you are an average weight male (84 kg) you'll want to aim for at least 67 grams (268 kcal) of protein per day (based on 0.80 g protein/kg body weight). Assuming you're consuming 2000 kcal per day, your goal is to get at least 13.5% of your food energy from protein.
Different food categories provide different amounts of protein. I'll calculate the average amount of food energy provided by protein across a basket of examples in each category.
- Fruits: 4.5% energy from protein (apple, banana, orange, mango, grapefruit)
- Grains: 10.2% energy from protein (rice, buckwheat, barley, oats)
- Vegetables: 12% energy from protein (onion, potato, kale, broccoli)
- Pulses: 21.0% energy from protein (chickpeas, lentils, black beans, navy beans)
Remember, based on our assumptions we want to get 13.5% of food energy from protein. We can't meet that target by eating only fruits, grains, and vegetables, but it's easy once we add in some pulses. Pulses are also a high source of the amino acid called lysine which makes them a great addition to our diet. We want to eat a bit of fruit, but if we eat too much it will get harder to meet our protein requirement.
It's a good idea to eat 3 servings of legumes/beans each day, especially when aiming to get all protein from whole plant foods.
If avoiding processed proteins, avoid oil and sugar too
There's one more category I haven't mentioned yet that is particularly challenging.
- Refined oils and sugars: 0% energy from protein (olive oil, candy, margarine)
Unlike the whole vegetable foods listed above, refined oils and sugars don't contribute any useful protein to the diet. Incorporating any of these foods makes it much more challenging to meet the protein requirement from whole foods alone. If the diet includes too much refined oils and sugars, then the protein requirement needs to be met in other ways such as with meat substitutes or protein powder or refined proteins like tofu and seitan.
All of the numbers I provided in this post were calculated using Cronometer, a web-based tool for adding up nutrient values of various whole and packaged foods.