10 . DIETARY PROTEINS

Protein function

Structure ➔ Function

Protein quality

ability of a protein to support growth

Quality determined by digestibility and AA composition when compared with a reference protein (egg white)

Amino acid score

analysis of protein for amino acid content

Ratio of EAA/NEAA that matches the human needs

High-quality protein (complete protein)

contains all 9 essential amino acids, with proper EAA/NEAA ratio

Highest quality protein foods: eggs, milk, meat, fish

Low-quality protein (incomplete protein)

contains most, but not all of the essential amino acids, with inadequate EAA/NEAA ratio

Best sources: grains, legumes

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

takes into account the percent digestibility of a food item

On average animal proteins have higher digestibility (80-90%) compared to plant proteins (<70%)

Protein complementation

combined consumption of a variety of plant proteins in order to provide sufficient amounts of all AA

Not only for a single meal, but over the entire day

Dietary proteins DRI + types

10 – 35%

Insect protein (crickets, grasshoppers, mealworms), animal + plant

Animal origin

Greater quality and content

More readily digested

Plant origin

Lesser protein content

Lower quality

Protein requirements

Amount of dietary protein varies with biological value

Less for animal protein, more for plant protein

The Dietary Guidelines for Americans (2025-2030) recommend 1.2-1.6 g/kg/d

Athletes (strength and resistance training) can increase to 1.6-3g/kg/d

Pregnant women should increase intake to 2g/kg BW/d

RDA for mixed biological value proteins

0.8 g/kg BW/d to prevent deficiencies

Plant-based diets

Benefits of vegetarianism

Health: Lower fat intake, Higher amounts of fiber

Ethical: Non-harmful to animals

Economic/environmental: Animal-derived protein involves high production costs and loss of natural resources

Benefits of vegetarian diets

Ease of meeting nutritional guidelines (lacto-ovo vegetarians)

Decreased incidence of obesity

Decreased incidence of hypertension

Lower risk for developing diabetes

Decreased risk for death from colon cancer, coronary heart disease

concerns of vegetarian diets

Caloric adequacy for pregnant females and children (primarily vegans)

Mineral (iron, zinc, calcium) adequacy (primarily vegans)

Vitamin B12, & D adequacy (vegans only)

Need for advanced nutritional knowledge (vegans only)

Dietary recommendations for vegetarians

Choose a variety of foods

Choose whole, unrefined foods

Choose a variety of fruits and vegetables

Choose dairy products and eggs in moderation

Consume a regular source of vitamins B12 and D

Fortified foods or supplements

Protein supplementation

Common among body-builders

Healthy, well-fed individuals do not have to supplement protein supplements

Recommendations:

• Supplement of carbs + protein after high-endurance exercise

• Complete nutritional supplements for elderly with decreased appetite or medically compromised

Excessive protein consumption

Americans consume on average the required amount of protein.

Consuming increased amounts of protein without endurance training

Excess is deaminated and C-skeletons are used for storage ➔ obesity

Urinary nitrogen excreted along calcium ➔ risk for osteoporosis, increased renal stress

Increased risk for heart disease and stroke

Increased incidence of colon cancer

Carbs and lipids have protein-sparring effect ➔AA used for tissue maintenance and repair

Protein-energy malnutrition (PEM)

Malnutrition: imbalanced nutrient intake, energy intake, or both

2 forms of PEM: marasmus & Kwashiorkor

Populations at risk in North America

• Homeless individuals living in shelters or other temporary sites

• Older adults

• Hospitalized patients: iatrogenic malnutrition

• Chronic hunger: working poor, whose incomes barely cover basic expenses of housing, utilities, and health care and leave little for food purchases

Marasmus

In developing countries, in children <1 year

Cause: long-term deficiency in protein and calories (calorie deprivation)

Symptoms:

• Extreme muscle wasting

• Depletion of subcutaneous fat = emaciation

• Reduction in cognitive ability due to impaired brain development

• Vitamin and mineral deficiencies

Kwashiorkor

In developing countries, when children are weaned from breast milk to a low-nutrient diet, high-CHO diet

Most common in children ages 18–24 months

Cause: sudden and recent protein deprivation > total calories reduction

Symptoms:
– Stunted growth
– Edema and ascites
– Fatty liver
– Skin lesions
– Defects in cellular immunity
– Deficiency of essential amino acids

Sarcopenia

Progressive and generalized loss of skeletal muscle mass and strength

Primary (age-related) or secondary (rheumatoid arthritis, malignancies, etc)

Recommendations
– 0.8 g/Kg BW/d appear insufficient to prevent sarcopenia progression
– 1.2–1.6 g/Kg BW/d may be more appropriate; others advocate even more
– Weight-bearing exercise and increased protein may stop sarcopenia

Protein food allergies

6 food groups account for 90% of food allergies

About 80% of young children with food allergies outgrow them, if they develop them before the age of 3

Food allergies diagnosed after 3 years are often long-lived

food allergy = food intolerance

implications for dentistry

Protein deficiency can affect the growth and development of oral tissues and structures

Delayed tooth eruption, enamel hypoplasia with increased risk for dental caries, permanent reduction in the size of the mandible, decreased cortical bone density, reduced tissue proliferation

Protein deficiency can also increase susceptibility to general and oral infections

Protein in excess can reduce calcium retention and subsequent bone health