Chapter 6: Protein - Comprehensive Study Notes

Protein in Food and Wellness

• Proteins are essential because they provide amino acids, the building blocks for the thousands of proteins that form every aspect of the human body.
• Protein is a super-nutrient for Americans, with multiple sources in the food supply.
• Common beliefs about protein (e.g., more protein = stronger immune system, more weight loss, more muscle) are not always accurate; intake often exceeds what the body needs.
• Five dimensions of health provide a framework to think about protein effects: physical, intellectual, emotional, social, and spiritual health.
• Essential concepts:
  • Essential amino acids (EAAs): 9 cannot be made by the body and must be eaten in food.
  • Nonessential amino acids (NEAAs): 11 can be synthesized in the liver from other amino acids.
  • The body maintains an amino acid pool that supplies EAAs and NEAAs for protein synthesis.
• Box 6-1 (MyPlate: Protein Foods) highlights that the protein group includes meat, poultry, fish, eggs, nuts, seeds, and dry beans/peas; emphasize lean cuts and fatty-acid quality (omega-3s in certain fish and nuts).
• Portion guidance (What Counts as an Ounce?):
  • 1 ounce-equivalent from the meat and beans group includes: 1 oz cooked lean meat; 1/4 cup cooked dry beans; 1 egg; 1 tablespoon peanut butter; 1/2 ounce nuts or seeds.
• Protein sources can also yield other nutrients (omega-3s, vitamin E, fiber, etc.).
• Important dietary considerations:
  • Choosing lower-fat protein sources can help reduce diet-related disease risk.
  • Vegetarian and other eating patterns may require attention to protein quality and variety.

Structure of Protein

• Proteins are organic compounds formed by linking amino acids via peptide bonds.
• Amino acids are organic compounds containing carbon, hydrogen, and oxygen, plus nitrogen (which distinguishes protein from other nutrients).
• There are 20 amino acids used to make all proteins in plants and animals.
• Essential amino acids (EAAs): 9 must be obtained from food; non-essential amino acids (NEAAs): 11 can be made by the liver from other amino acids.
• The liver can synthesize NEAAs as long as nitrogen and other structural components are available.
• The amino acid pool is the circulating supply of amino acids available for protein synthesis.
• Protein structure is described in four levels:
  • Primary: the sequence and number of amino acids in a polypeptide chain.
  • Secondary: local folding stabilized by hydrogen bonds (e.g., alpha helices, beta pleated sheets).
  • Tertiary: the three-dimensional shape maintained by intramolecular bonds and hydrogen bonds.
  • Quaternary: association of more than one polypeptide chain.
• Peptide bonds form when the carboxyl group of one amino acid bonds to the amino group of the next amino acid, releasing a molecule of water. A schematic representation:
  ext{AminoAcid}1{-} ext{COOH} + ext{AminoAcid}2{-} ext{NH}2 ightarrow ext{AminoAcid}1{-} ext{CO}{-} ext{NH}- ext{AminoAcid}2 + ext{H}2 ext{O}
• Factors that denature proteins (alter their three-dimensional shape) include heat (cooking), ultraviolet light, acids, alcohol, and mechanical action. Denaturation can aid digestion but may impair function if structure is irreversibly altered.
• Within the body, denaturation is controlled to maintain homeostasis; extreme pH can denature vital body proteins.
• Example: beating egg white denatures its proteins, turning a clear liquid into a white, foamy solid, while amino acids remain intact.

Protein Digestion and Absorption

• Mouth: mechanical digestion only; mastication reduces particle size; saliva mixes with food.
• Stomach:
  • Pepsinogen (inactive) is secreted by the stomach mucosa.
  • Hydrochloric acid (HCl) activates pepsinogen to pepsin.
  • Pepsin begins protein hydrolysis, producing smaller polypeptides.
  • Rennin (gastric protease) is produced only during infancy; with calcium, it thickens casein to slow gastric emptying, aiding digestion in infants.
• Small intestine:
  • Pancreatic and intestinal proteases continue hydrolysis of polypeptides.
  • Peptidases released by the intestinal wall finish hydrolysis to amino acids and dipeptides.
  • Primary pancreatic enzyme: trypsin (secreted as trypsinogen and activated by enteropeptidase).
  • Other pancreatic enzymes: chymotrypsin and carboxypeptidase; dipeptidases and aminopeptidases complete hydrolysis.
  • Absorption occurs via competitive active transport in the intestinal walls; vitamin B6 (pyridoxine) acts as a carrier.
  • Because amino acids are water-soluble, they readily enter the bloodstream.
• Protein metabolism and function rely on the amino acid pool; most dietary proteins are broken down to amino acids before synthesis of body proteins.

Protein Composition, Denaturation, and Nutrient Roles

• The four structural levels of protein (as above) determine function; changes in shape can alter function.
• Denaturation in the body is a normal part of digestion; it increases surface area for digestive enzymes.
• Hydrolysis and absorption of amino acids supply the body’s amino acids for tissue growth, maintenance, and various functions.

Protein Metabolism and Nitrogen Balance

• Protein metabolism is largely governed by anabolism (synthesis) and catabolism (breakdown).
• Hormonal regulation:
  • Anabolism is enhanced by growth hormone and testosterone.
  • Catabolism is promoted by glucocorticoids (regulated by ACTH) and occurs during stress, illness, and fasting.
• Nitrogen balance concepts (based on nitrogen input and output, since protein contains nitrogen):
  • Equilibrium/zero nitrogen balance: nitrogen intake equals nitrogen excreted.
  • Positive nitrogen balance: more nitrogen retained than excreted (growth, pregnancy, wound healing).
  • Negative nitrogen balance: more nitrogen excreted than retained (muscle breakdown, illness, injury).
• Deamination (removal of an amino group) produces ammonia (NH₃) and a keto acid; the liver converts most ammonia to urea for excretion via urine. The keto acid can enter:
  • The TCA cycle for energy, or
  • Gluconeogenesis to form glucose, or
  • Lipogenesis to form fat.
  • schematic:
    ext{AminoAcid}
    ightarrow ext{NH}_3 + ext{Keto acid}
    ightarrow ext{urea} ext{ (excreted)} ext{ or } ext{energy/glucose/fat}
• Protein excess: high protein intake increases deamination and keto acids, potentially leading to ketosis and greater urea excretion; the liver and kidneys may be stressed; no clear benefits to excessive protein intake. Recommendation: consume no more than twice the RDA for protein.
• Kidney and liver health considerations: high animal-protein diets can be high in saturated fat and cholesterol, increasing risk for CAD and some cancers. The relationship with osteoporosis is mixed and multifactorial.
• RDA and intake guidelines:
  • The RDA for protein is $ext{RDA} = 0.8 \frac{ ext{g}}{ ext{kg}} imes ext{body weight (kg)}$
  • For an average adult man: roughly $58-63 \frac{ ext{g}}{ ext{day}}$
  • For an average adult woman: roughly $46-50 \frac{ ext{g}}{ ext{day}}$
  • Pregnant: +$71\frac{ ext{g}}{ ext{day}}$; Lactation: +$71\frac{ ext{g}}{ ext{day}}$
  • Athletes: $1.2-1.7 \frac{ ext{g}}{ ext{kg}} ext{ depending on endurance vs. strength}$
• The Acceptable Macronutrient Distribution Ranges (AMDRs) suggest protein should provide between 10 ext{–}35 ext{%} of energy intake.

Diet, Protein Quality, and Measurement

• Protein quality assessment methods:
  • Biologic value (BV): measures how much nitrogen from a protein is retained after digestion; egg is the reference with BV = 100.
  • Amino acid score: assesses amino acid composition relative to a reference protein; focuses on the limiting amino acid; does not consider digestibility.
  • Protein Efficiency Ratio (PER): based on weight gain in rats fed a protein; a comparative measure of physiologic value.
• Typical BV ranges: egg ~100; fish ~75–90; corn ~40 (lower due to limiting amino acids).
• Complete vs incomplete proteins:
  • Complete proteins contain all nine EAAs in adequate amounts; typical complete sources include animal products (meat, poultry, fish, eggs, dairy) and soybeans (tofu).
  • Incomplete proteins lack one or more EAAs (many plant foods such as many grains and legumes).
• Box 6-4 lists sources of complete vs incomplete proteins and notes a notable exception: gelatin is incomplete.
• Complementary proteins: by combining plant foods across the day (or in the same meal), you can achieve a complete amino acid profile. Examples include: grains + legumes; grains or legumes with small amounts of animal protein.
• Practical plant-based meal examples (combinations that yield complete protein):
  • Grains + Legumes (e.g., rice + beans, lentil soup with bread)
  • Grains + Legumes + Animal Protein (small amounts, e.g., chili with beans and meat, pasta with cheese)
• Box 6-5 demonstrates practical combinations that provide complete protein from plant and animal sources.

Vegetarianism and Diet Patterns

• Vegetarianism is increasingly popular for health, environmental, ethical, and spiritual reasons.
• Vegetarian categories:
  • Vegan: all plant foods; excludes all animal-derived foods.
  • Lacto-vegetarian: plant foods + dairy (milk, cheese, yogurt, butter).
  • Ovo-lacto vegetarian: plant foods + dairy + eggs.
  • Pescetarian: plant foods + dairy + eggs + fish; excludes meat from land animals.
  • Flexitarian: largely vegetarian with occasional meat, fish, or poultry.
• Benefits of well-planned vegetarian diets:
  • Reduced risk of diet-related diseases, lower total fat and cholesterol, higher fiber, and potential environmental and ethical benefits.
  • Plant-based diets tend to include more magnesium, folic acid, vitamins C and E, iron, zinc, and phytonutrients.
  • Body weight often lower, reducing risk of hypertension and type 2 diabetes.
• Drawbacks and nutrients of concern for vegans (and sometimes ovo-lacto vegetarians):
  • Vitamin D and B12 deficiencies (B12 only in animal foods; fortified foods or supplements recommended for strict vegans).
  • Calcium, iron, zinc, and omega-3 fatty acids require careful planning.
  • Vitamin D can be gained via sun exposure or fortified foods; many people have suboptimal vitamin D levels.
• Social and practical considerations: social eating challenges; importance of planning, protein complementing, and vegetarian nutrition education; MyPyramid guidance supports vegetarian patterns.
• Contemporary vegetarian patterns include pescetarian and flexitarian variations that incorporate fish or occasional meat to ease nutrient balance while maintaining health benefits.

Cultural and Religious Considerations in Protein Consumption

• Kashrut (Jewish dietary laws): kosher guidelines with eight basic rules, supervision by rabbis, and labeling (e.g., a distinctive K on packaging).
  • Acceptable animals: cloven-hooved mammals that chew the cud; acceptable birds (e.g., chicken, duck, geese, turkey); fish with fins and scales; shellfish, eel, catfish not permitted.
  • Slaughter must be quick and painless with blood drained; certain parts and nerves avoided; meat and dairy are not eaten together; pareve foods can be eaten with either category; insects/worms checked; kosher certification visible on packaging.
• Halal (Islamic dietary laws): foods permissible unless specifically prohibited; pork and birds of prey prohibited; animals must be slaughtered according to Muslim procedures; alcohol and drugs that alter consciousness prohibited unless medically necessary; caffeine-containing beverages (coffee/tea) discouraged by some.
• Application to nursing: respect dietary restrictions of clients, and adapt treatment and nutrition plans accordingly (e.g., insulin sources and dietary considerations).

Diet Planning and Meal Formatting

• Restructuring the Dinner Plate for protein planning: shift from large meat-centered portions to balanced plates.
  • Original plate example (Figure 6-5): large meat portion; total protein may exceed daily needs if not balanced.
  • Restructured plate (Figure 6-6): protein distributed more evenly among plate items; total protein remains adequate when portions are balanced.
  • Deck-of-cards method (Figure 6-7): use the size of a deck of cards to estimate a portion of animal-protein; the palm-sized portion is a typical expected serving.
• Example: a 6-ounce chicken serving provides about $53 ext{ g}$ of protein; a 3-ounce portion provides about rac{53}{2} ext{ g}
  ear 26.5 ext{ g} of protein; combined with other plate items, total daily protein can be met without oversized meat portions.
• MyPyramid guidance supports vegetarian patterns and provides energy and nutrient adequacy when properly planned.

Malnutrition and Protein Energy Nutrition Disorders (PEM)

• PEM is an umbrella term for malnutrition due to lack of protein, energy, or both.
• Marasmus: malnutrition due to a severe energy deficit; appears extremely thin with little subcutaneous fat and muscle wasting; potential brain impact if in critical developmental windows (e.g., 6–18 months).
• Kwashiorkor: malnutrition due to protein deficiency with adequate energy intake; edema (swollen belly and cheeks), fatty liver, hair changes, skin dermatitis, apathetic behavior, muscle weakness, poor growth.
• Aflatoxin connection: mold toxin found in grains stored under poor conditions; aflatoxin poisoning can impair liver function, increase risk of liver cancer, and worsen PEM outcomes by reducing NEAA production in the liver; aflatoxin exposure can suppress immune function and worsen malnutrition.
• Global burden: PEM accounts for roughly half of the annual 10.9 million child deaths; regional distribution: ~70% Asia, ~26% Africa, ~4% Latin America/Caribbean.
• Definitions and evolving concepts:
  • Kwashiorkor defined as protein deficiency with adequate energy; modern research recognizes multifactorial contributions (infection, toxins, energy balance, aflatoxins).
  • PEM can cause permanent developmental deficits in children due to critical brain growth periods.
• Severe malnutrition risk factors include poverty, food insecurity, inadequate education, and environmental factors such as poor water quality and famine.
• At-risk populations in North America include the homeless and working poor, who may face chronic hunger due to financial and housing instability; hospital malnutrition (iatrogenic malnutrition) can occur due to illness, treatments, or procedural factors that limit nutrient intake or absorption.
• Malnutrition is influenced by biologic, social, economic, and environmental factors (Box 6-6):
  • Biologic: maternal malnutrition, infections, chronic diarrhea, aflatoxin exposure.
  • Social: lack of nutrient knowledge, abuse/neglect, eating disorders, social isolation, alcoholism.
  • Economic: poverty, unemployment, low education, political strife affecting food systems.
  • Environmental: polluted water, famine, poor farming techniques.

Nutrition and Clinical Practice: Planning and Patient Education

• Chaining: linking two behaviors to form a habit; strategies include:
  • Pair a protein-containing food with a routine (e.g., sandwich + fruit; milk with lunch).
  • Use portion-control cues (e.g., weigh portions and compare to a deck of cards).
• Case study: Protein (Wound Healing) – Roy, a 69-year-old homeless male with a leg ulcer who is undernourished.
  • Assessment: limited intake of protein foods; physical signs of undernutrition; albumin 2.7 g/dL (norm 3.4–4.8 g/dL); stage II ulcer.
  • Diagnoses: imbalanced nutrition; impaired skin integrity related to inadequate nutrition.
  • Nursing interventions:
  • Educate on protein importance for wound healing; identify high-protein foods and portions (deck-of-cards guidance).
  • Provide high-protein snacks/supplements; ensure adequate calories and vitamins (A, C, zinc) for wound healing.
  • Wound care and debridement as ordered; support housing and shelter access for consistent nutrition and rest.
  • Planning and evaluation: short-term and long-term goals, with follow-up and progress toward healing and weight gain.
• Teaching tools:
  • Calculation tool: to determine personalized protein intake.
  • Steps: divide body weight by 2.2 to get kg; multiply by 0.8 g/kg to get RDA; e.g., 63.5 kg × 0.8 g/kg = 50.9 g/day.
  • For athletes and special conditions, refer to the higher-end estimates (1.2–1.7 g/kg).

Practical Examples and Tables (Highlights)

• Box 6-1 provides MyPlate protein foods and recommended portions; emphasizes variety and nutrient co-variation (e.g., omega-3 fatty acids in fish, vitamin E in nuts).
• Box 6-2 lists amino acids (EAAs vs NEAAs) and their classifications/complementarity in protein synthesis.
• Box 6-3 discusses the buffering role of proteins in acid-base balance, based on amino acid structure (carboxyl group COOH and amine group –NH2 can act as acid or base depending on pH).
• Box 6-4 lists sources of complete vs incomplete proteins (e.g., eggs and dairy as complete; most grains as incomplete; soybeans as complete among plant sources).
• Box 6-5 shows protein-complete meal combinations (e.g., grains + legumes; grains + animal protein with small amounts; grains/legumes with dairy).
• Box 6-6 outlines malnutrition factors across biologic, social, economic, and environmental domains.
• Box 6-7 (deck of cards) illustrates a simple visual for portion sizes and protein planning on meals.

Summary Teaching Points

• Protein quality and quantity are both essential: aim for adequate EAAs via diverse protein sources and complementary plant proteins when not using animal products.
• RDA for protein is a baseline; many individuals (e.g., athletes, pregnant/lactating persons) require higher intakes; the AMDR for protein is 10–35% of total energy intake.
• Vegetarian diets can meet protein needs with careful planning to ensure complete amino acid profiles and adequate micronutrients (B12, D, calcium, iron, zinc, omega-3s).
• PEM (marasmus and kwashiorkor) remains a global concern; aflatoxins can worsen PEM by impacting liver function and NEAA production.
• In clinical settings, assess and address malnutrition early (e.g., through nursing assessments, nutrition support teams, and multidisciplinary care).
• Practical dietary planning can be aided by tools like the deck-of-cards portion size method and the restructuring of meals to distribute protein across meals rather than concentrating it in one dish.

Equations and Quick References (LaTeX)

• Protein RDA: $ext{RDA} = 0.8 \frac{ ext{g}}{ ext{kg}} imes ext{body weight (kg)}$
• General AMDR for protein: 10 ext{–}35 ext{ ext{% of energy intake}}
• Athletes’ protein range (example): $1.2 ext{–}1.7 \frac{ ext{g}}{ ext{kg}}$
• Average adult protein needs (examples): Man ≈ $58 ext{–}63 \frac{ ext{g}}{ ext{day}}$; Woman ≈ $46 ext{–}50 \frac{ ext{g}}{ ext{day}}$
• Pregnancy/lactation additional protein: $+71 \frac{ ext{g}}{ ext{day}}$
• Dietary protein quality: Egg has BV ≈ 100 as reference; Fish BV ≈ 75–90; Corn BV ≈ 40.
• Peptide bond formation (simplified):
  ext{AminoAcid}1{-} ext{COOH} + ext{AminoAcid}2{-} ext{NH}2 ightarrow ext{AminoAcid}1{-} ext{CO}{-} ext{NH}- ext{AminoAcid}2 + ext{H}2 ext{O}
• Deamination (protein metabolism):
  ext{AminoAcid}
  ightarrow ext{NH}3 + ext{Keto acid} ext{NH}3
  ightarrow ext{urea (urine excretion)}
• Nitrogen balance concepts:
  • Equilibrium: $ext{N intake} = ext{N excretion}$
  • Positive balance: $ext{N retained} > ext{N excreted}$
  • Negative balance: $ext{N excreted} > ext{N retained}$

Teaching Tools and Resources

• Teaching Tool: Calculating Your Recommended Protein Intake (step-by-step): 1) Weight in pounds ÷ 2.2 = weight in kilograms (kg) 2) Multiply kg by 0.8 g/kg to determine RDA in g/day
  • Example: 140 lb ÷ 2.2 = 63.6 kg; 63.6 × 0.8 ≈ 50.9 g/day
• Practical application: For athletes or special conditions, use higher ranges (1.2–1.7 g/kg).
• Wound healing case demonstrates integrated care: protein adequacy, calories, vitamins (A, C), zinc, and engagement with social support systems (shelter) to promote healing.

Notes on References and Scope

• This content aligns with nutritional science principles on protein structure, digestion, metabolism, and dietary planning.
• Cultural, social, and practical dimensions (vegetarianism, religious dietary laws, and health disparities) are integrated to reflect real-world considerations in nutrition care.