Proteins Health Article

Protein requirements

On a per kilogram basis, protein requirements in humans are highest in infancy and gradually decline throughout one's life, except in such circumstances as pregnancy, lactation, and illness. The Recommended Daily Allowance (RDA) suggests protein requirements based on age incrementally. The amount of protein needed also depends on body weight, but it is not a linear relationship. A person who weighs 400 lbs (181.43 kg). does not need four times as much protein as a person weighing 100 lbs (45.35 kg). From birth to three months, protein needs are at their highest (2.2 grams per kilogram of body weight). The requirement for adult males and females is 0.8 g/kg. This amount is equal to about 63 grams of dietary protein for a male aged 25-50 years who weighs 174 lbs. (79 kg), and 50 grams for a female aged 25-50 years who weighs 139 lbs. (63 kg). The average Western diet contains ample amounts of protein. In fact, most people in industrialized countries eat more protein than they need. In the United States, true protein deficiency is rare except when excess protein is lost and protein requirements are increased, as in cases of:

• burns
• fever
• fractures
• surgery
• wasting and/or cachexia associated with cancer (Approximately half of all cancer patients experience cachexia, a wasting syndrome that induces metabolic changes leading to a loss of muscle and fat.)
• chronic renal failure, when the patient is undergoing hemodialysis or peritoneal dialysis

Protein requirements may also be increased in training athletes because of greater muscle mass during training season.

In general, consequences of inadequate protein intake may include a faster loss of muscle mass from the body; higher risks of infection; and reduced protein reserves for use during periods of trauma or infection. In addition, protein breakdown is rapid when a person is fasting or bedridden.

Dietary sources of protein

Meat, milk, eggs, poultry, and seafood are considered high-quality, "complete" proteins because they have all the essential amino adds (protein's building blocks) in just the right proportion. Those sources are considered more complete than vegetable protein, such as beans, peas, and grains, also considered a good—even if not complete—source of amino acids. Except for soy, plant sources—nuts, beans, seeds, and grains—are deficient in one or more of the essential amino acids. But plant foods contain other vital nutrients (such as phytochemicals and fiber) not found in animal foods. Dietitians recommend that a healthy diet should consist of foods from a variety of sources and should include 10–20% of daily calories from protein (poultry, fish, dairy, soy protein, nuts, legumes, eggs, peanut butter, and vegetable sources).

Dietary guidelines

The food pyramid, developed by nutritionists, provides a visual guide to healthy eating. At its base are those foods that should be eaten numerous times each day, while at its apex are those foods that should be used sparingly. The pyramid suggests a range of servings in each group so that the number of servings can be adjusted to suit each individual's caloric requirements. The daily recommendations (from bottom to top) of the food pyramid include:

• Bread, cereal, rice, and pasta: 6–11 servings.
• Vegetables: 3–5 servings.
• Fruits: 2–4 servings.
• Milk, yogurt, and cheese: 2–3 servings.
• Meat, poultry, fish, dried beans, eggs, and nuts: 2–3 servings.
• Fats, oils, and sweets: use sparingly.

Protein-modified diets

High-protein diets are designed to provide about 1.5 g of protein for each kilogram of a person's body weight. Complex proteins, such as milk and meats, should make up one-half to two-thirds of the daily protein requirement. High-protein diets are recommended for people who:

• Have an increased need for protein due to protein-calorie malnutrition; severe stress; or such conditions as AIDS, cancer, or burns with high metabolic rates that lead to the loss of large amounts of protein.

• Have malabsorption syndromes, celiac disease, or other disorders characterized by poor food absorption.

A low-protein diet excludes dairy products and meats, and requires that about three-fourths of the daily allowance of protein come from high-value protein sources. Supplements may be prescribed to prevent amino-acid deficiencies. Low-protein diets are used in treatment of conditions such as liver cirrhosis and kidney disease (excluding chronic renal failure patients who have increased protein needs because of losses that occur during dialysis).