Metabolic Medical Center

Proteins are the basic constituents of all living organisms and part of the structure of plants. In the human body, every living cell and all body fluids except bile and urine contain protein. It is the main component of muscles, organs and glands. It makes up 80% of the dry weight of muscle, 70% of the dry weight of skin, and 90% of the dry weight of blood.  The cells of muscles, tendons and ligaments are maintained with protein.  It is absolutely necessary for good growth and development from birth through adolescence.  At every stage in life, the body depends on a steady inflow of animal and/or plant protein for the synthesis of its own proteins.
The chemical definition of protein: protein is a complex molecule made up of amino acids.  Through natural functions, the body can make over half of the amino acids that it needs.  It depends upon food to supply the rest.  If a food can supply all of the amino acids that the body lacks, it is called complete protein; if a food does not supply all of the amino acids that the body lacks, it is called incomplete protein.  The protein in fish, shellfish, meat, poultry and their related products, such as milk, cheese and eggs, supplies all of the amino acids that the body needs to make its own protein, and, therefore, is complete protein. 

No singular plant protein contains all of the necessary amino acids.  However, nuts, certain beans and grains can be combined to supply them.  An understanding of these combinations is essential for a healthy vegetarian diet.
The American diet has come to include large daily servings of protein, especially the protein in meat.  It is very important to follow the recommended portions of protein for your diet.  Once you understand the reason why, you will find yourself to be very interested in monitoring your protein intake.   When you eat more protein than you need, your body does not take the extra dietary protein and make more protein than usual.  Instead, your body breaks down the extra dietary protein, turns as much of the amino acids as it needs into glucose to be used for energy, and turns what's left over into fat.  

The easiest way to supply the body with the necessary amino acids is through a diet that includes the complete protein in poultry, fish, meat and meat products.  However, in choosing the source of protein, you should examine the plus and minus qualities of the foods in these categories. 
Poultry:   With all skin removed and all visible fat trimmed off, poultry easily beats meat when the amount of protein is compared to the amount of calories and fat in each.  In the category of poultry; which includes chicken, turkey, and Cornish hens; the white meat of chicken and turkey rates highest, containing the most protein in relation to calories and fat.  Cornish hens and the dark meat of chicken and turkey come in second, but still considerably higher than meat.  For ease in cooking (who would want to remove the skin from a turkey before it is cooked!), it is helpful to know that cooking poultry with its skin on does not appreciably increase its calories or fat.  If the skin is not removed before consumption, however, the calorie count and number of fat grams increase dramatically.
Fish:  Like poultry, fish is an excellent source of protein.   Fish also offers an additional asset that is not found poultry, meat or meat products: the presence of Omega-3 fatty acids. Omega-3 fatty acids are highly polyunsaturated fatty acids that have been proved to prevent sudden heart attacks, help the clotting of blood, reduce LDL (bad cholesterol) and raise HDL (good cholesterol), and are believed to reduce the risk of heart disease in general.  People with diabetes and arthritis may also benefit.
Cold-water, "oily" fish, tuna, canned tuna in water, salmon, canned salmon, mackerel, herring, and sardines, contain the highest Omega-3 concentration, but it is found, though in lesser concentration, in cod, whitefish, bass and trout.  Fresh tuna also has a unique heartiness, so that for many people a piece of grilled tuna can be as satisfying as a piece of grilled steak.  It is necessary to eat a minimum of two servings of fish per week to achieve the Omega-3 benefits.
Shellfish:   When broiled, boiled or steamed, clams, mussels, oysters, scallops, shrimp, lobster, and crab are good sources of low-fat, low calorie protein, but within this category there are also pluses and minuses.   Surprisingly, since they are thought of as rich foods, oysters and lobsters have the least calories per ounce; it's the tartar sauce and the melted butter that has given them a bad reputation. Mussels and crab contain Omega-3 acids. Shrimp, unfortunately, is high in cholesterol and sodium.
Eggs and Egg Substitutes:  Frequently called the "prefect protein package," the egg offers a good source of protein because, although there is protein in the yolk, the protein in the white has not fat in it.  Since all of the fat is in the yolk, the egg can provide 100% fat-free protein if only the white is used.  Further, separating the fat (the yolk) from the protein (the white) is easy and there is no inner marbling of fat to contend with as there is in most meat.  In standard large eggs there is 1/2 ounce of protein per white. 
New feed formulas used by several egg producers have produced an even more nutritious egg, allowing you to feel better about enjoying an occasional whole egg.  For example, Eggland's Best, available in local grocery stores, raises its chicken on a patented all-vegetable feed that is high in rice bran, alfalfa meal, kelp and canola oil.  The results show up in the yolk.  It has 25% less saturated fat than a standard egg, 25% of the RDA of vitamin E (six times higher than the standard egg), and 100 mg of Omega-3 fatty acid. 
Egg substitutes are available in two basic forms – dry and liquid.  Anything labeled a true “egg substitute” must not contain any egg product at all.  This usually refers to the dry product, which is a combination of various starches and gums.  Dry substitutes are used predominantly in baking and have a shelf life of 6 months or more if stored in a cool dry place.  Liquid substitutes like EggBeaters will normally contain a mix of egg whites and cholesterol free additives.  The main variance between the different liquid egg products is the calorie count and fat content.  Most are non-fat but a few do include added fat.  Most liquid egg products are sold either refrigerated or frozen and have freshness dates printed on their cartons.  The refrigerated shelf life is similar to that of cream based products.  In the freezer, they can be stored safely for 3 months or more.
Meat:   Even in the meat category, certain cuts are healthier than others.  Lean cuts are preferable, trimmed of all skin and possible fat, and include the following:

 

Meat Products, Milk, Yogurt, and Cheese: Along with protein, milk products provide vitamins and minerals, and are the best source of calcium.  Almost all milk products are available in natural low-fat and/or no-fat forms and are acceptable for adding variety to a healthy diet.  However, when consumed alone, fat-free milk and yogurt rank high on the insulin index; a little fat (low-fat) in milk and yogurt slows the release of insulin that they trigger.
Hard, highly flavorful cheese like Parmigiano-Reggiano (Parmesan) and Romano are great "condiments" -- small amounts of these cheeses provide more flavor per ounce.   Otherwise, you should eat only low-fat or fat free cheese, ideally with 3 grams or less of fat per ounce, and even these should be limited to consumption once or twice a week.
Finally, but very importantly, stick with natural milk products.  Processed cheese food and imitation whipped toppings usually contain undesirable additives, and in some cases, unhealthy hydrogenated fat.

 

For vegetarians, and others desiring a more plant-derived diet, certain beans, grains, nuts and seeds can be combined to provide complete protein. Familiar combinations are peanut butter sandwiches, hummus on pita, rice and black bean salad.  But remember that although these combinations can supply complete proteins, they are still made up of carbohydrates and will need to be counted as carbohydrate portions in your diet.
Nuts:  New York Times Personal Health columnist Jane Brody says this about nuts: "Packed with the nutrients needed to start a new generation of plants; nuts are increasingly being recognized as powerhouses of health-promoting substances, especially for people who need to lower their cholesterol, triglycerides or blood pressure." Nuts also provide antioxidants, vitamins and minerals -- including important foliates -- calcium, magnesium and potassium. While 72% to 90% of their calories are derived from fat, with the exception of walnuts and pine nuts, most of the fat found in nuts is healthy monounsaturated fat. Walnuts, surprisingly, offer a helping of Omega-3 fatty acids. Be cautious, however, for no matter how beneficial, at an average of 160 calories per ounce (think 6 Brazil nuts or 10 raw peanuts); nuts should be eaten in moderation.
Beans:  The beans that contribute to making combinations of complete protein are the legumes: cow peas, chick peas, crowder peas, black-eyed peas, black beans, lentils, lima beans, butter beans, kidney beans, white beans, and split peas. See more about beans under Carbohydrates.
Soybeans:  Although the soybean is a legume, and can be used in bean and grain combinations, it is the only legume that actually is a complete protein and, as such, does not have to have a complimentary grain.  Soy products are extremely popular today, and not only with vegetarians.  In America, the soybean is most commonly made into soymilk and various forms of tofu.  Soft, sometimes called "silken," tofu can be used in sauces and healthy drinks (smoothies).  In its firm form, it can be incorporated into dishes either by crumbling it or cutting it into a desired size. It has a blandness that brings protein to a dish without changing its flavor.  It tastes best cubed and sautéed until it achieves a crust, and served hot. This also produces good texture, somewhat like fried cheese - tastily crisp outside and creamily smooth inside.  The only downside to soybean products is that, ounce for ounce the soybean has more calories than any of the other legumes, white meat of poultry, and some fish and shellfish.
Grains:  The simplest way to remember what grains are really good for you is to "Think Brown."  While all grains, from white rice to white bread, will supply some protein, it is the whole grains that supply the most nutrients and are the best for you. Grains have another good protein combination that is very familiar: grains and dairy products (cheese toast, cereal with milk, muesli with yogurt).  In this category, remember to look at the various degrees of calories and fat in the dairy products.  This is the place to use skim milk and fat-free yogurt because when combined with grains, especially whole grains, the insulin release is slowed down.  
The category of grains is a particularly effective place to get the value from eating a variety of foods.  Many people eat the same kind of bread and cereal every day, day after day. Most people never look beyond the wheat pastas. They may use whole wheat bread and steel-cut oatmeal.  But there are a number of other grains that are quite effectively used to make bread, pastas and cereals.  Health food stores have breads made from spelt and sprouted wheat, which is more nutritious than whole wheat, Once seen only in health food stores, most grocery stores now have pasta made of quinoa or spelt and cereals made with multi-grains.  In addition to whole wheat, corn and oat, the whole grains most frequently in multi-grain cereal are quinoa, spelt, and kamut.