Proteins - Diet and Nutrition

Proteins

All humans require proteins to survive because they regulate virtually every bodily function. Approximately 20% of the human body consists of proteins, including the skeleton, muscle fiber, hair, skin, and nails.

Once a protein-containing food such as meat is eaten, the protein is broken down in the stomach into different amino acids. The human body needs 20 different amino acids to function, although it can only actually manufacture 12 of these itself. The eight most important amino acids that cannot be manufactured internally must be obtained from animal and plant protein foods. These eight essential amino acids–called so because the body requires them for optimal cell functioning–are phenylalanine, tryptophan, valine, threonine, lysine, isoleucine, leucine, and methionone. If they are not present, some normal body processes will be impaired. Consuming the right amount of food each day is extremely important in order to supply the proper amount of the eight essential amino acids.

The difficulty for many people lies in knowing exactly how much protein their bodies need each day and which foods contain the right amounts of the required amino acids. Nutritionists agree that adults need approximately 50–60 grams daily, which is fulfilled easily by a normal American's diet of meat, fish, eggs, and dairy products. Although both meat and plant foods contain proteins, meat is a better source because it contains all eight essential amino acids. Most vegetables are lacking in at least one essential amino acid and consequently vegetarians usually need to consume both grains and legumes to obtain their amino acid requirements.

If people consume too little protein, they will develop symptoms of a protein deficiency. Children who do not eat enough protein, for example, will have retarded skeletal and muscle growth. Pregnant women who do not eat enough protein will suffer from poor weight gain and fatigue. Adults who lack protein often have weak immune systems, which make them susceptible to infections and diseases. This is because proteins form a critical part of the antibodies which protect the body from viruses and bacteria.

Obtaining adequate amounts of high-quality protein is not a problem for most people in developed countries. In fact, most Americans consume twice the amount of protein they actually need, two-thirds of which comes from meat. Overconsuming protein is potentially dangerous because an excess of protein eaten at any one time cannot be fully absorbed by the body. This excess protein then enters the blood stream as partially digested protein (peptides), which are now thought to cause inflammation of some organs, tissues, and joints.

Scientists have begun to link the consumption of too much meat protein to other health problems such as cancer and heart attacks. Americans who eat large amounts of meat tend to have higher rates of cancer of the colon, for example, although scientists are not yet sure precisely why. Most meat sold commercially, according to Gordon Edlin and Eric Golanty, also contains nonfood chemicals such as pesticide residues and hormone growth promoters, all of which may be co-contributors to cancer. Overconsumption of animal fat, especially the fat in red meat, also appears to increase men's risk of developing prostate cancer. Scientists at Harvard University and the Mayo Clinic compared the health records and eating habits of more than 47,000 American men by dividing them into two groups: those who ate large amounts of red meat and those who did not. The men whose diets included large quantities of red meat were more than 2 1/2 times as likely to develop cancer as those who ate little red meat. And according to an article in the Journal of the American Medical Association (JAMA) , reviewed in the October 6, 1993 issue of the San Francisco Chronicle , eating excessive amounts of protein-rich meat (which is also high in fats and cholesterol) can lead to heart disease.