knowt logo

Dietary Protein

AMDR for protein: 10% - 35%

  • provides the essential amino acids

Protein Quality

Protein Quality: a measure of a dietary proteins’ ability to provide the essential amino acids (EAA) required for tissue maintenance

Protein Digestibility-corrected amino acid score (PDCAAS): the standard adopted to evaluate protein quality, based upon the profile of essential amino acids and digestibility of protein.

  • highest score: 1.00

  • provides a method to balances intakes of poorer-quality proteins with high-quality proteins

Proteins from animal sources:

  • meat poultry, milk and fish

  • high quality (contain all the EAA and are more readily digested)

    • Gelatin is an exception, it has low biological value

Proteins from plant sources:

  • lower quality than animal proteins

  • proteins from different plant sources may be combined to form high biological value

    • e.g. wheat (lysine deficient but methionine rich) may be combined with kidney beans (methionine poor but lysine rich)

Nitrogen Balance

Nitrogen balance: amount of nitrogen consumed equals that of the nitrogen excreted.

  • most normal healthy adults are normally in nitrogen balance

Positive Nitrogen Balance

Positive nitrogen balance: nitrogen intake exceeds nitrogen excretion

Occurs in situations in which tissue growth is observed:

  • childhood

  • pregnancy

  • convalescing

Negative Nitrogen Balance

Negative nitrogen balance: nitrogen loss is greater than nitrogen intake.

Associated with:

  • inadequate dietary protein

  • lack of an essential amino acid

  • during physiological stress

    • trauma

    • burn

    • illness

    • surgery

Protein Requirements

  • amount of dietary protein required varies with its biological value

  • disease states influence protein needs

    • protein restriction may be needed in kidney disease

    • burns require increased protein intake

  • recommended intake: 0.8g/kg/day

  • people who exercise strenuously on a regular basis may benefit from extra protein to maintain muscle mass

    • daily intake of: ~1g/kg/day

  • pregnant or lactating women require up to 30g/kg in addition to their basal requirements

  • infants should consume 2 g/kg/day

Consumption of excess protein:

  • no physiological advantage to the consumption of more protein than the RDA

  • protein consumed in excess of the body’s needs is deaminated

    • the resulting carbon skeletons are metabolized to provide energy or acetyl CoA for fatty acid synthesis

  • when excess is eliminated from the body as urinary nitrogen, it is often accompanied by increased urinary calcium, increasing the risk of nephrolithiasis (kidney stones) and osteoporosis

The protein-sparing effect of carbohydrates:

  • dietary protein requirement is influenced by the carbohydrate content of the diet

    • if carbohydrate intake is low amino acids are deaminated to provide carbon skeletons for the synthesis of glucose that is needed as fuel for the central nervous system

    • if carbohydrate intake is less than 130 g/day sustainable amounts of protein are metabolized to provide precursors for gluconeogenesis

  • carbohydrate allows amino acids to be used for repair and maintenance of tissue protein rather than for gluconeogenesis

Protein-energy (calorie) malnutrition (PEM)

  • also known as protein-energy undernutrition (PEU)

  • in developed countriess it is mostly seen in patients with medical conditions that:

    • decrease appetite

    • alter how nutrients are digested or absorbed

    • in hospitalized patients with major trauma or infections

      • often require intravenous or tube-based administration of nutrients

  • may be seen in children or elderly who are malnourished

  • inadequate intake of protein and/or energy is the primary cause of PEM in developing countries

  • symptoms include depressed immune system, reduced ability to resist infection

  • secondary infections can lead to death

Two extreme forms of PEM:

  • Kwashiorkor

  • Marasmus

Kwashiorkor

  • protein deprivation is relatively greater than the reduction in total calories

    • associated with severely decreased synthesis of visceral protein

  • commonly seen in developing countries in children after weaning at about the age of 1 year

Typical symptoms:

  • stunted growth

  • skin lesions

  • depigmented hair

  • anorexia

  • edema (results from the lack of adequate blood proteins to maintain the distribution of water between blood and tissues)

  • fatty liver

  • decreased serum albumin concentration

Marasmus

  • calorie deprivation is relatively greater than the reduction in protein

  • usually occurs in children younger than 1 year of age

    • when the mother’s breast milk is supplemented with thin watery gruels of native cereals, which are usually deficient in protein and calories

Typical symptoms:

  • arrested growth

  • extreme muscle wasting and depletion of subcutaneous fat (emaciatation)

  • weakness

  • anemia

LA

Dietary Protein

AMDR for protein: 10% - 35%

  • provides the essential amino acids

Protein Quality

Protein Quality: a measure of a dietary proteins’ ability to provide the essential amino acids (EAA) required for tissue maintenance

Protein Digestibility-corrected amino acid score (PDCAAS): the standard adopted to evaluate protein quality, based upon the profile of essential amino acids and digestibility of protein.

  • highest score: 1.00

  • provides a method to balances intakes of poorer-quality proteins with high-quality proteins

Proteins from animal sources:

  • meat poultry, milk and fish

  • high quality (contain all the EAA and are more readily digested)

    • Gelatin is an exception, it has low biological value

Proteins from plant sources:

  • lower quality than animal proteins

  • proteins from different plant sources may be combined to form high biological value

    • e.g. wheat (lysine deficient but methionine rich) may be combined with kidney beans (methionine poor but lysine rich)

Nitrogen Balance

Nitrogen balance: amount of nitrogen consumed equals that of the nitrogen excreted.

  • most normal healthy adults are normally in nitrogen balance

Positive Nitrogen Balance

Positive nitrogen balance: nitrogen intake exceeds nitrogen excretion

Occurs in situations in which tissue growth is observed:

  • childhood

  • pregnancy

  • convalescing

Negative Nitrogen Balance

Negative nitrogen balance: nitrogen loss is greater than nitrogen intake.

Associated with:

  • inadequate dietary protein

  • lack of an essential amino acid

  • during physiological stress

    • trauma

    • burn

    • illness

    • surgery

Protein Requirements

  • amount of dietary protein required varies with its biological value

  • disease states influence protein needs

    • protein restriction may be needed in kidney disease

    • burns require increased protein intake

  • recommended intake: 0.8g/kg/day

  • people who exercise strenuously on a regular basis may benefit from extra protein to maintain muscle mass

    • daily intake of: ~1g/kg/day

  • pregnant or lactating women require up to 30g/kg in addition to their basal requirements

  • infants should consume 2 g/kg/day

Consumption of excess protein:

  • no physiological advantage to the consumption of more protein than the RDA

  • protein consumed in excess of the body’s needs is deaminated

    • the resulting carbon skeletons are metabolized to provide energy or acetyl CoA for fatty acid synthesis

  • when excess is eliminated from the body as urinary nitrogen, it is often accompanied by increased urinary calcium, increasing the risk of nephrolithiasis (kidney stones) and osteoporosis

The protein-sparing effect of carbohydrates:

  • dietary protein requirement is influenced by the carbohydrate content of the diet

    • if carbohydrate intake is low amino acids are deaminated to provide carbon skeletons for the synthesis of glucose that is needed as fuel for the central nervous system

    • if carbohydrate intake is less than 130 g/day sustainable amounts of protein are metabolized to provide precursors for gluconeogenesis

  • carbohydrate allows amino acids to be used for repair and maintenance of tissue protein rather than for gluconeogenesis

Protein-energy (calorie) malnutrition (PEM)

  • also known as protein-energy undernutrition (PEU)

  • in developed countriess it is mostly seen in patients with medical conditions that:

    • decrease appetite

    • alter how nutrients are digested or absorbed

    • in hospitalized patients with major trauma or infections

      • often require intravenous or tube-based administration of nutrients

  • may be seen in children or elderly who are malnourished

  • inadequate intake of protein and/or energy is the primary cause of PEM in developing countries

  • symptoms include depressed immune system, reduced ability to resist infection

  • secondary infections can lead to death

Two extreme forms of PEM:

  • Kwashiorkor

  • Marasmus

Kwashiorkor

  • protein deprivation is relatively greater than the reduction in total calories

    • associated with severely decreased synthesis of visceral protein

  • commonly seen in developing countries in children after weaning at about the age of 1 year

Typical symptoms:

  • stunted growth

  • skin lesions

  • depigmented hair

  • anorexia

  • edema (results from the lack of adequate blood proteins to maintain the distribution of water between blood and tissues)

  • fatty liver

  • decreased serum albumin concentration

Marasmus

  • calorie deprivation is relatively greater than the reduction in protein

  • usually occurs in children younger than 1 year of age

    • when the mother’s breast milk is supplemented with thin watery gruels of native cereals, which are usually deficient in protein and calories

Typical symptoms:

  • arrested growth

  • extreme muscle wasting and depletion of subcutaneous fat (emaciatation)

  • weakness

  • anemia

robot