Remember those charts of the basic food groups your teacher pointed to in grade school?
Protein was usually represented by a thick steak surrounded by drawings of a fish and a chicken. The healthful meal centered around meat, with some green or yellow vegetables and bread to round it out. Protein, and lots of it, was thought to be the key to a sound diet.
The amount of protein the average American eats hasn't varied much since the turn of the century. We've been eating more than enough all along. But our grandparents got more of their protein from plant sources like grains and beans, and less from animals.
In that respect, because of higher fiber and lower fat content, their diet may have been more healthful than ours.
Plants have fiber that we need to keep our digestive tract running smoothly and to reduce our chance of colon cancer. Beef lacks fiber and doesn't provide as much protein as you think. Even when you trim all the fat from a cut of beef, only a quarter of what is left is protein. The rest is primarily fat and water.
Protein is essential to keep your body moving; it forms the muscles that move your bones. Enzymes composed of proteins control the continual chemical reactions that keep you alive. These proteins are complex molecules, and each cell in your body contains thousands of them--even fat cells contain some protein.
All of our protein molecules are built within the cell they will serve. Protein molecules are made of smaller building blocks, the amino acids; an average of 150 amino acid molecules form a protein molecule. It's at the amino acid level that we focus our task of following a proper diet so our bodies can continue to form new protein cells and keep us going. When we eat a piece of meat, we break down its protein molecules into amino acids.
Human protein is made up of about 20 different amino acids, each of them a long string of carbon, hydrogen, nitrogen, oxygen and sometimes sulfur. Eight of these are called the essential amino acids, essential because our body can't make them out of other amino acids. They must be present in our diet.
Animal protein is a quality source of amino acids because it has a good mix of those amino acids we need the most. The highest quality protein source is the egg white, or albumen, in which each molecule of protein contains 418 units of amino acid. In assessing the quality of protein source, scientists use egg white to judge all others.
Vegetable protein is free of cholesterol, but doesn't have as nice a mix of amino acids as does animal protein. Generally, only one or two of the essential eight are present, and in negligible amounts. Fortunately, however, for those who prefer to eat less meat or none at all, you can obtain a good mix of amino acids by combining different plant sources. We don't know yet whether or not we can do this over the course of the day, so it's best to be sure that each meal has the right combinations.
Mexican Beans and Rice
The Mexican dietary custom of eating rice and beans together is a good idea. Legumes (beans) and grains (rice) are excellent plant sources of amino acids and, when combined, form a good quality protein source. Legumes include peas, beans, lentils, peanuts, chickpeas (garbanzo beans) and soybeans. The soybean (and soy products like tofu) is the best single plant protein source.
How much protein do you need? The Recommended Daily Allowance is 44 grams a day for an adult woman and 56 grams for an adult male. These numbers are inexact because your protein demand is based on your age and weight--the more cells your body has, the more grams you need.
It's more accurate to say that you need .38 of a gram of protein per day for every pound you weigh. For example, if you weigh 110 pounds (or if that's your ideal body weight), you should eat at least 42 grams of protein. Half a pound of chicken, fish or lean meat would be more than enough, since each supplies 56 grams of protein. Six ounces of cooked meat provides 42 grams of protein. You would get almost that much by eating a hamburger a day (even the bun has 4 grams).
If you exercise regularly, you probably need more protein than someone who is sedentary, to make sure you don't burn your body's stored protein. At the same time, your body can process only a certain amount of protein each day--the rest is eliminated. So you don't have to eat a whole chicken every day or take protein pills. You need no more than .68 of a gram per pound you weigh (75 grams for a 110-pound woman), and if you're like most Americans, you already consume about 100 grams a day.
One of the best reasons not to ingest a lot more protein than you actually need is the presence of fats and cholesterol in animal protein sources. Too many calories from protein can also contribute to weight gain--as excess stored fat. A 3-pound steak can contain as many as 300 calories.