Macronutrients, DRIs, and Protein Functions

• Macronutrients such as carbohydrates, fats, and protein are energy sources from diet.
• Ethanol is not an essential nutrient, but it significantly contributes to daily caloric intake.
• Essential fatty acids & amino acids, vitamins and minerals make up a healthy diet.
• Dietary Reference Intakes (DRIs) estimates nutrient intakes to prevent deficiencies and maintain optimal health.
• Upper levels are also included in DRI's
• DRIs refer to average intake over time, not just daily intake.

Components of Dietary Reference Intakes

• Estimated Average Requirement (EAR) is the intake at which the risk of inadequacy is 50%.
• Recommended Dietary Allowance (RDA) is the intake at which the risk of inadequacy is 2-3%.
• Adequate Intake (AI) does not bear a predictable relationship to the EAR or RDA; it's based on estimates of healthy people's nutrient intake..
• Tolerable Upper Intake Level (UL) is the point above which the risk of adverse effects increases.

Protein Functions

• Goal is to maintain sufficient protein in the diet to replace degraded amino acids.
• Unlike fats and carbohydrates, there is a requirement for protein in the diet.
• Growing children need more protein due to increases in body size.
• Adults continually lose protein through shedding skin cells, enzymes, and proteins secreted into the gut as well as tissue turnover and mucin.
• The total amount of protein in adult body do not change necessarily.
• Dietary protein intake should equal 80g with 10g lost in fecal matter and 70g in urine.

Amino Acid Functions

• Glycine is a key intermediate in heme synthesis and is required for detoxification in the liver.
• Glycine is the principal inhibitory transmitter in the brain stem and spinal cord, and it occurs at every third amino acid residue in collagen.
• Tryptophan is a precursor of the neurotransmitter serotonin (5-hydroxytryptamine).
• Histidine is decarboxylated to histamine, which has immune response and physiological functions in the gut.
• Arginine is a precurosr of nitric oxide and creatine
• Lysine residue interacts with glutamine when factor XIIIa converts a low tensile strength fibrin polymer into a high tensile strength clot.
• Glutamine is a substrate for protein synthesis, controlling acid-base balance through renal ammoniagenesis.
• Glutamine is a substrate for hepatic ureagenesis and gluconeogenesis.
• Glutamine is a fuel for intestinal enterocytes and acts as an ammonia scavenger.
• It is a substrate for citrulline and arginine synthesis, acting as a nitrogen donor for nucleotides, amino sugars, and coenzymes.
• Glutamine transports nitrogen (1/3 of circulating N) and stimulates glycogen synthesis and arginine NO metabolism.

Meeting protein and AA needs

• Nutritional quality of food proteins depends on the content of indispensable amino acids (AAs) and their availability for host metabolism.
• First-class proteins include animal proteins, while second-class proteins are plant proteins.
• Protein quality refers to its ability to provide essential amino acids for tissue maintenance.

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

• PDCAAS is a standard to evaluate protein quality.
• It is based on the profile of amino acids and digestibility of the protein.
• The PDCAAS value for egg and milk protein is 1.00.
• The PDCAAS value is 0.82-0.92 for beef/poultry/fish and 1.00 for Soybeen
• Kidney beans are rich in lysine with 0.68 PDCAAS
• Whole wheat bread scores 0.40 with deficient lysine

Nitrogen balance

• Positive nitrogen balance: intake exceeds excretion, occurs during tissue growth.
• Negative nitrogen balance: loss exceeds intake, caused by inadequate dietary protein or essential amino acids, or during physiological stress.
• Nitrogen balance = Total body protein does not change.
• Positive nitrogen balance = Total body protein increases.
• Negative nitrogen balance = Total body protein decreases.
• High protein diets increase water loss from the kidneys, causing dehydration

Protein Loss from Trauma

• Fracture of femur presents 900g total loss
• Muscle wounds may lead to 1350-1900g total loss
• 35% burns may lead to 1400-1650g total loss
• Typhoid Fever presents 685g total loss

Protein Requirements

• Adults need 0.8g/kg of body weight.
• Athletes need approximately 1.0g/kg.
• Pregnant/lactating women need 30g/day.
• Children need 2g/kg/day.

Protein-Energy Malnutrition (PEM)

• Pure Protein deficiency: results in Kwashiorkor disease in children.
• Energy Deficiency: results in Marasmus.
• PEM Leads to Reduced number of T lymphocytes and Defects in generation of phagocytic cells and production of immunoglobulins, interferons
• Normal inflammation from glucocortoids and interleukins leads to increased lipolysis and proteolysis
• This can then causes low rates of serum albumin or decreased cellular immunity
• Secondary infection, not starvation, commonly leads to death.

Excess Protein

• Excessive protein intake increases protein-breakdown products (e.g. urea) and water loss.
• It causes problems if kidneys cannot concentrate urine.
• Immature kidneys of infants can lead to dehydration
• Its also a risk for those with kidney disease

Amino Acid Absorption & Absorption of Protein Fragments

• Amino acids with similar structures use same transport systems; excess of one slows adsorption of another.
• AAs compete with each other with Lysine
• Protein fragments undigested can cause Allergies
• Food allergies are triggered when a protein is absorbed before completely breaking it down in digestion.
• The Essential Amino Acids include Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine.

Essential and Non-Essential Amino Acids

• Arginine is semi essential where Infants need it the most
• Cysteine is derived from methionine and tyrosine, while phenylalanine is converted to tyrosine.
• Alanine, Aspartate, and Glutamate can be converted to Pyruvate, Oxaloacetate and a-KG, respectively.

Macronutrients, including carbohydrates, fats, and proteins, provide energy. DRIs estimate nutrient intakes to prevent deficiencies and maintain health, including EAR, RDA, AI, and UL. Protein functions are also vital for overall health.