As a seasoned vegetarian, it never ceases to amaze me that when someone discovers my dietary preference, the first question they ask is, "Do you know you're not getting enough protein?"
It also never ceases to amaze me how incredibly strong the filters in my brain are - the ones that keep me from responding with, "Do you know there's undigested meat putrifying in your colon?" One of these days, one of those brain filters is going to blow....
So anyway, my standard response is, "So how much is 'enough'?"
Since the answer I get is usually something along the lines of, "Well, more than you can get from [insert carrots/lettuce/twigs/other non-dietary-staple here]," I thought I'd do a bit of research and gain some insight from someone who knows what the hell they're talking about.
As with most things nutritional, you ask 10 different "experts", you get 10 different answers. But most tend to express daily need as a factor of a person's body weight (grams of protein/day per lb. of body weight), and virtually all hover in the .35 - .45 range for a sedentary person, .40 - .60 for a moderately active person, and .60-.90 for an athlete or bodybuilder.
So... I am a 135 lb active adult. That means I should be getting somewhere between 54 and 81 grams of protein per day. Well, let's look at my food intake yesterday (a not-particularly-health-conscious day, as I was on the go from 5 A.M to about 9:30 PM) and see what we come up with:
1 8 oz. glass soy milk - 7 grams
2 oz trail mix - 5 grams
1 Bagel - 9 grams
Vegetarian Pad Thai - 11 grams
Spring Roll - 3 grams
Lentil Soup - 18 grams
French bread - 5 grams
8 oz soy milk - 7 grams
Total = 65 grams
65 grams is well within range, and as I stated earlier, I wasn't even being good yesterday.
Other foods I regularly consume that have moderate to high protein content, per the USDA Nutrient Database for Standard Reference, Release 18, 2005:
Seitan - 31 grams for 3 oz.
Black beans - 15 grams for 1 cup
Chickpeas (an Indian food staple) - 12 grams for 1 cup
Veggie burger (hey, I'm a busy guy) - 13 grams
Spinach - 5 grams for 1 cup
Spaghetti noodles - 8 grams for 1 cup
Broccoli - 4 grams for 1 cup
Tofu - 11 grams for 4 oz.
So I'm not too worried about running out of steam. And if you're contemplating a meat-free diet, rest assured that it can be done in a very nutritionally sound way. The above foods are vegan, so even if you make that step, there's nothing to worry about.
Now, I'm not going to sit here and tell you that your best friend's weird cousin Ingrid, who is a proud vegetarian but subsists on potato chips, veggie dogs, and beer, is doing just fine and gets enough protein in her diet. Just like omnivores, vegetarians and vegans have to use a modicum of common sense regarding what they eat. For every pale, skinny vegetarian, there's a flabby, bloated "normal person" who eats at McDonalds every other meal and wonders why that flight of stairs is so hard to climb. That's just the way it is.