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