That's one of the most frequent questions I hear when discussing plant-centered eating. I hear it at the gym, where I work, from medical professionals, fitness experts, fellow cooks, and knowledgeable friends.
My favorite answer "I love broccoli. Broccoli is loaded with protein."
But not everyone likes broccoli. Or they don't believe me when I say I get protein from broccoli. You mean in the whole history of humankind, vegetarians were dieing from lack of protein? Now we know! Really, though, my question for them is "How much protein do you need?" and then "How much are you getting?"
The tricky part here comes with the math. Now, I love math and numbers. Some people don't. The simple math:
Let's take a healthy female. She's 140 (64 kg) lbs, moderately active.
She needs about 1600 calories a day.
RDA is .8 grams of protein per kilogram of weight. For our healthy female, that's about 51 g of protein. 1 gram of protein is 4 calories, so that means 204 of her calories should come from protein (about 8 percent of her total calories for the day).
If you love more math, check out my friend Jeff Novick's post on Protein Requirements. He's a Registered Dietician and takes a calculator to the grocery. He loves math.
So, back to broccoli.
98 calories of broccoli has 28 calories (more than 28%) protein. When doing the math, remember 1 gram of protein = 4 calories. I won't even get into the fiber, vitamin A, vitamin C, calcium, or iron that also comes with broccoli. You probably already know all of that. If our healthy female ate only broccoli (1600 calories worth!) all day, she'd get 114 g of protein by the end of the day.
100 calories of oats has about 20% protein. Oats! A day of only oats would be 69g of protein
Tomatoes. 32 calories of tomatoes (that's a whole cup of tomato slices!) has 25% protein. (2 grams of protein = 8 calories. 8/32 = 25%) A day of 1600 calorie tomatoes? 100g of protein.
I haven't made a single mention of beans, lentils, nuts, or tofu. I also haven't mentioned fake-meat products or processed products. When we eat food that is stripped of its bran and fiber (aka refined flours, sugars, and oils), we strip it of its protein. Then we usually pay for it in a bright shiny label that advertises "now with extra protein". Pass on the labels. Eat your broccoli.