Daily protein requirement

Mar 2014   › › › Daily protein requirements
Protein requirement for the human body quite relative and variable controlled by several biological processes. Daily protein necessity depends upon an individual's gender, age, height and weight.
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Relative amounts of other macronutrients like carbohydrates and fats in the diet also alters the body's demands for proteins. The level of physical activity of a person and his lifestyle also have an effect over his necessities of all the macronutrients.

Daily protein requirement and the spectrum of amino acids

The physical and chemical composition as well as the nutritive value of proteins have high degree of variances. Generally the nutritive value is measured analytically in terms of nitrogen it is contributing. There are diverse types of proteins formed from different combinations of amino acids and their sequences in the molecules. They contribute differently to meet the daily requirement of the body for growth, maintenance and repair.

Two major factors are to be considered while assessing the quality of this macronutrient. Digestibility is an important factor as some molecules of the nutrient may not be easily digestible. The digestibility has a direct bearing on the daily requirement. Nearly 20-25 percent of the daily nitrogen consumption is excreted in feces. This is partially due to the physical and chemical composition of the molecule which renders it resistant to breakdown by digestive enzymes for absorption. Some nitrogen is also lost on a daily basis in the form of secretions in the gastrointestinal tract.

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    • The second factor is the amino acid composition. Protein has to be broken down to the constituent amino acids for absorption by the body to meet its daily requirements. The human body can synthesize several amino acids. However, it cannot synthesize certain amino acids which known as essential amino acids.

    These essential amino acids are our daily requirements and our diet must contain them. The deficiency of these amino acids can affect the biological processes such as protein synthesis and the related cellular metabolic activities. A paradox situation arises in our diet wherein the protein content of a particular food is very rich but lacking in some essential amino acids makes it of lesser food value.

    Protein requirements for protein turnover

    In protein turnover, these macronutrients are being continuously broken down and resynthesized in our body. It is estimated that in an adult more than 250 g of this macronutrient is synthesized and broken down daily. In the infants protein turnover is high whereas in elderly people it is less.
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    • The intestine and liver are believed to contribute to more than 50% of the turnover. As the essential amino acids are also lost in the turnover daily requirements arise to make good the loss.

    Protein requirements for energy

    When there is energy restriction due to malnutrition or other factors this macronutrient contributes significantly to the energy by its oxidation. However this process leads to huge loss of protein from the body. This oxidation is also found to be at a high rate in septic or traumatized individuals. It is recommended that "adults should get 45 percent to 65 percent of their calories from carbohydrates, 20 percent to 35 percent from fat, and 10 to 35 percent from protein. Acceptable ranges for children are similar to those for adults, except that infants and younger children have necessity for a slightly higher proportion of fat (25-40 percent)" (Food and Nutrition Board).

    Given below is the abstract of the Recommended Dietary Allowances of protein for various age groups by Institute of Medicine's Food and Nutrition Board.

    Adequate Intake for Infants: 0 Through 6 Months
    0–6 months - 1.52 g/kg/daily

    RDA for Older Infants:
    7–12 months 1.2 g/kg/daily

    RDA for children Ages 1 - 13 Years
    1–3 years 1.05 g/kg/daily
    4–8 years 0.95 g/kg/d
    9–13 years 0.95 g/kg/d

    Adolescents Ages 14 years - 18 Years:
    RDA for Boys and girls 14–18 years 0. 85 g/kg/daily

    Adults Ages: 19+:
    RDA for Men and women 0.80 g/kg/d

    RDA for Pregnancy
    In pregnant women additional requirements arise in the last two trimesters of about 25 g/d over and above the pre-pregnancy requirements.
    All age groups 1.1 g/kg/d or +25 g/d of additional necessities

    RDA for Lactation:
    All age groups 1.3 g/kg/d or +25 g/d of additional requirements

    Individuals on active sports and muscle building will have higher protein requirements.
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