When it comes to the area of proteins, the description of food as building blocks is even more directly true than ever. Although most of us think of proteins in terms of muscle and (possibly) hair/fingernails, proteins are an important part of our entire body -- from "scaffolding" for cell walls to acting as catalysts for general digestion.
However, protein eaten does not directly translate to protein built in the body. The body's digestive processes break down proteins into building blocks called amino acids. It then uses these amino acids, as determined by specific gene sequences, to create the proteins the body needs. There are 20 or 21 (depending on how you classify them) amino acids used within the human body. Some of these can be created by the body from general food (that is, not amino acids). Others can be created from other amino acids (changed from one to another). Some, however, must be eaten and these are the "essential" amino acids.
Essential amino acids must be part of a regular diet -- but that doesn't mean they all have to be eaten each day. The body just must have a reserve of them in the "storehouse".
Meat has the advantage in that the animal has already gathered up, or created, the various amino acids needed. However, it is fully possible to get all the needed amino acids from a varied vegetarian diet. The mixes needed to have a complete set are called "complementary" foods. Beans and rice work as complementary" foods. Lentils and barley are a great combination. There are many others.
As mentioned, meats give "complete" sets of proteins -- whether it be beef, poultry, fish, pork or some other meat from animals. Beef often gets a bad name as a meat. This is not because of the protein but, rather, from the saturated fat that is often mixed in with the protein. Depending on the particular cut of meat and the way that it is prepared, it is possible to have very lean, healthy, beef as a part of a meal. In fact, if you prepare poultry in a high-fat manner (think fried chicken), chicken can have higher levels of fat than beef. Fish is often separated from other types of meat because the fat which it contains is normally UNsaturated (including "Omega-3" (linoleic) acids). Thus, fish protein is lean and the oils that come with it are recommended types of oils.
In the area of economics, meat is an expensive choice. This is largely because it is higher on the "food chain". In the U.S., at the grocery store, chicken can average $3/pound, turkey $1.50/pound, fresh fish may cost $7/pound (depending on geographic location). It is difficult to spend less than $1.50/pound for meat but it is possible to spend more than $50/pound for particular cuts of meat or specially prepared meat or varieties of animal meat. On the other hand, a combination of lentils and barley (enough for a single person) may only cost 30 cents ($0.30). If you choose the vegetarian route then you have three advantages -- cost, a light footprint on the earth (less of earth's resources used) and an automatic advantage in not getting "unhealthy" fats (allowing you to choose what fats to incorporate within your meals). The disadvantage is that you MUST vary your diet deliberately in order to have what your body needs.
One additional disadvantage of animal meats should be mentioned. This is the fact that most meats available at grocery stores are "factory meats". The animals have been treated as raw materials to produce meat. Not only are these methods not kind to the animals but the process requires antibiotics and hormones to keep the animals alive long enough to harvest. The factory meat process is probably the largest reason for waves of recalls of contaminated meat. (Note, however, that vegetable products are not immune to this -- the recent recall of peanut products.). While you can get non-factory meat, it will be more expensive and it still requires a lot of food (particularly grain products) to produce.
I love a good hamburger -- and bacon must truly be set into a class of its own. However, I also love a good lentil and quinoa salad. We are designed to be omnivores and, as long as we are aware of what we eat, we can get good protein into our diet in many different ways.
