I've always had a certain respect for vegetarians. Though some see them as overly sentimental, or perhaps needlessly orthorexic, I see people willing to sacrifice for their values. And I do mean sacrifice.
There is the fact, first of all, that meat tastes good. Some will argue with me on this point, but I'm a firm believer that just about every person has some animal flesh they enjoy consuming. There's just too much of it out there, and too many flavor and texture profiles, for that not to be the case.
But I think the larger sacrifice has to do with health. Now this, admittedly, goes very much against the current trend. Bill Clinton and Mike Tyson are now vegan, and everyone from Hollywood to Harvard is advocating for a diet higher in plants, and lower in animal products. If we're speaking purely about environmental and global economic issues, then I have no qualms. But, though I'm no nutritionist, I find the idea that abstaining from meat entirely is not a practice that confers optimal health.
Ok, fine. Whatever. What does this have to do with coffee? I'm getting to that, actually.
A vegetarian diet, almost by definition, is going to be deficient in several nutrient categories. Protein is the most discussed, and oddly, the easiest to meet without meat. There are plenty of decent protein sources that aren't animal flesh available to vegans, and even more if you allow milk and eggs. Granted, plant sources tend to be less concentrated, lack certain amino acids, and be less bio-available. But even still, vegans are not generally in any great risk of suffering from protein deprivation.
There is vitamin B12, which is not readily found in any plants. It is, however, in most fortified things and multivitamins. And since coffee has nothing to do with this, I'll say no more.
Iron is another story. People only really think of this nutrient in the context of women -- typically, those of middle age or more. But everyone needs it, especially if you're an avid exerciser (and I think everyone really ought to be). The best sources, however, are meat. Nuts and soy have some, as do legumes, but the phytates contained in these foods make the iron much more difficult to absorb. By some estimations, vegetarians need as much as twice the amount of iron meat eaters do, in order to compensate for this fact.
Now here's where coffee comes in. Coffee is, in general, a healthy beverage. I've said as much before, and I firmly believe it to be true. But even healthy things have nits to be picked, fringe concerns which might be magnified in certain contexts. Vegetarianism is the context in which coffee consumption might have one deleterious effect. Coffee, when consumed around the time you're eating food, makes iron less available to the body. If you're a meat eater, this isn't really a problem, as there's enough iron in your food that you can get away with not absorbing all of it. But for vegetarians, this can be an issue.
Not enough of one, however, that coffee need be avoided. The easiest fix is to consume your beans and spinach separately from your coffee. But if you're like me, and drinking the stuff all day, this isn't too practical. Thus we have the best option: A multivitamin with iron, or an iron supplement. Granted, supplemental iron is non-heme, that is, from a plant. Thus, it is the less bio-available variety. But chances are, the dose is significant enough that, provided you aren't subsisting on coke and fries, a vegetarian diet can supple enough iron, even in the face of rampant coffee consumption.
Of course, you could just eat the steak.