Macronutrients: Proteins

"Quirks" of RDA Recommendations for Proteins

DRI based on body weight and growth needs

Common sources of protein in diet

Animal products

Whole grains

Seeds/Legumes

Tofu

Amino acids

Functional unit of a protein. Consists of a carbon molecule bonded to an amino group, carboxyl group, and side chain

Essential Amino Acids

Amino acids that must be obtained through diet as the body cannot synthesize these amino acids on its own

• Histidine

• Isoleucine

• Leucine

• Lysine (becomes Arginine)

• Methionine

• Phenylalanine

• Threonine

• Tryptophan

• Valine

Non-essential Amino Acids

Amino acids that the body can synthesize on its own

• Alanine

• Asparagine

• Aspartic Acid (Aspartate)

• Glutamic Acid (Glutamate)

• Serine

Conditionally Essential Amino Acids

Amino acids that are normally considered nonessential but may becomes essential through certain conditions, such as lack of a key reactant, organ damage, or genetic disorders

• Arginine

• Cysteine (cystine)

• Glutamine

• Glycine

• Proline

• Tyrosine

Amino Acid Pool

Term to describe all of the amino acids in the body. The amino acid pool is dynamic and constantly changing

Protein Synthesis

Proteins are synthesized by ribosomes during translation. Since most proteins contain every single amino acid and a deficiency of one amino acid will stop translation of the entire protein, all amino acids must be present within the body for protein synthesis to occur

Limiting Amino Acid

The essential amino acid that is in it's lowest available concentration in the body (commonly methionine -> the START protein)

Nitrogen Balance

Comparison of nitrogen intake and nitrogen loss

Negative Nitrogen Balance

Nitrogen Intake < Nitrogen Output

Common from hospitalization and malnutrition

Positive Nitrogen Balance

Nitrogen Intake > Nitrogen Ouput

Common during pregnancy, child, bodybuilding

Plant-Based Protein Recommendations

-Plant based proteins sources are safe to eat as long as they are complemented with a combination of foods that contain all of the essential amino acids

-Plant based milk should not be used as a replacement for breastfeeding or formula for baby feeding

Complete Dietary Protein

Protein sources that contain all of the essential amino acids in a porportion similar to human needs.

Includes animal-based protein sources

Incomplete Dietary Protein

Protein sources that is deficient in some of the essential amino acids relative to human needs.

Includes plant-based protein sources

Protein complementation

Combining foods with different essential amino acid compositions to provide a diet that contains all of the essential amino acids needed by humans.

Often includes combining proteins from grains and legumes

Benefits of Plant-Based Protein Diet

-Lower risk of all-cause and CVD-related mortality

-Lower body weight

-Lower incidence of key chronic diseases (CVD, Diabetes, Cancer)

Drawbacks of Plant-Based Protein Diet

May result in higher risk of protein deficiencies due to lack of protein-rich options and lack of complete + high-quality protein sources. This can lead to deficiency of proteins and key nutrients (vitamin B12, calcium, Vitamin D, Iron, Zinc, Omega 3 FAs)

Risk can be mitigated through dietary planning (protein complementation) and supplements

Protein Quality

A measure of how efficiently a protein in the diet can be absorbed and used to make body proteins

Protein Quality Metrics Include:

-Amino acid score

-Protein efficiency ratio

-PDCAAS

-DIAAS

Amino Acid Score

A measure of protein quality that compares the amino acid composition of a protein compared to a model reference protein (often eggs)

A higher quality protein will have a composition that is similar to the reference protein

Protein Efficiency Ratio

A measure of protein quality that compares the weight gain of a protein compared to the weight gain of a model reference protein.

A higher quality protein will cause more weight gain (greater growth)

PDCAAS

Aka protein digestibility-corrected amino acid score

A measure of protein quality that assesses protein amino acid composition and digestibility.

Amino acid composition is assessed by comparing it to the needs of children aged 2-5

Amino acid digestibility is assessed by assessing fecal nitrogen content to determine how well the amino acids was absorbed

(less nitrogen in feces = less protein wasted = more protein absorbed)

DIAAS

Aka digestible indispensable amino acid score

A measure of protein quality that is similar to PDCAAS, however, instead of assessing digestibility through fecal nitrogen content, amino acid digestibility is measured via the end of the small intestine.

This is thought to be more accurate that PDCAAS as gut microbiota in the large intestine metabolize amino acids as well, which may skew digestability results

Protein-Energy Malnutrition

A disorder characterized by insufficient consumption of protein +/- energy leading to muscle wasting and increased susceptibility to infection.

Common in areas of the world where food insecurities is common and among impoverished individuals

Classified as Kwashiorkor or Marasmus

Kwashiorkor Disease

A form of protein energy malnutrition marked by a protein deficiency with appropriate caloric intake.

Increased risk in the older sibling of a family with a newborn infant (infant prioritized for breastfeeding, older sibiling switches to inadequate adult diet)

Characterized by a bloated belly as a result of fat accumulation in the liver from lack of lipoproteins and a loss of plasma colloids, leading to fluid accumulation/third spacing

Results in poor growth, increased infection risk, and changes to skin and hair

Marasmus Disease

A form of protein energy malnutrition marked by a protein and calories deficiency, resulting in a total negative energy balance

Affects entire family, including younger infants, compared to Kwashiorkor

Characterized by ketosis (compensation for low energy), impaired growth, and decreased intelligence due to impaired brain development