Lecture 12 (Units 15 and 16) Oct 16, 2025 D2L

Proteins are made of chains of amino acids.

Essential amino acids are those that the body cannot produce sufficiently and must be obtained from the diet.

Non-essential amino acids are those that the body can produce on its own, so they do not need to be obtained from the diet.

If a cell is building a protein and cannot find a needed amino acid, the synthesis stops.

The non-essential amino acids (NEAA) include:

• Glycine
• Cysteine
• Aspartic Acid
• Glutamine

The essential amino acids (EAA) include:

• Valine
• Threonine
• Tryptophan
• Alanine
• Proline
• Asparagine
• Arginine
• Serine
• Tyrosine
• Glutamic Acid
• Leucine
• Isoleucine
• Methionine
• Phenylalanine
• Lysine
• Histidine

Humans need all 20 amino acids to be able to make proteins.

The primary structure of a protein is a sequence of amino acids connected in a chain, representing the unique sequence that determines the protein's identity.

The secondary structure of proteins is characterized by hydrogen bonding of the peptide backbone, which causes the amino acids to fold into repeating patterns such as pleated sheets and alpha helices.

The tertiary structure refers to the three-dimensional folding pattern of a protein, which is determined by interactions among the side chains of the amino acids, crucial for the protein's functionality.

The quaternary structure of a protein is defined as a structure consisting of more than one amino acid chain, such as in proteins like hemoglobin, DNA polymerase, and ion channels.

All proteins have primary, secondary, and tertiary structures. The quaternary structure is present only in some proteins.

Denaturation of proteins can occur due to exposure to:

• Heat
• Acids
• Bases
• Alcohol
• Heavy metals

Positive effects of protein denaturation include:

• Cooking: Denatures food proteins, such as egg whites, making them safe to eat.
• Stomach acid: Opens protein structures for digestion, facilitating nutrient absorption.

Negative effects of protein denaturation include:

• Fever: Can denature body proteins, potentially leading to dysfunction.
• Heavy metals: Such as mercury, can destroy body proteins, causing toxic effects through:
  • Protein precipitation
  • Enzyme inhibition
  • Generalized corrosive action

• Mechanical breakdown of product matrix
• Hydrolysis of starch

Digestion by pepsin

• Digestion by pancreatic enzymes (chymotrypsin, trypsin, etc.) and brush border enzymes
• Absorption of amino acids and peptides

• Nitrogen absorption and recycling
• Microbial metabolism of protein, peptide, amino acids, and metabolites

A negative nitrogen balance occurs when the body loses more nitrogen than it takes in. This condition is often seen in:

1. Trauma patients
2. Astronauts

1. Building materials for muscle, fetus, scar tissue, red blood cells, and intestinal cells.

2. Maintenance of osmotic pressure in bodily fluids.

3. Synthesis of substances such as hemoglobin, antibodies, enzymes, hormones, plasma proteins, and coagulation factors.

Protein provides 4 kcal/gram of energy, similar to carbohydrates. However, unlike carbohydrates and fats, protein contains nitrogen. This nitrogen can be used for protein formation or excreted as urea by the kidneys if in excess.

Excess protein cannot be stored in the body like carbohydrates (stored as glycogen) or fats (stored as triglycerides). There is no storage form of protein; instead, it is broken down and used as needed.

Gluconeogenesis is the process where amino acids are converted to glucose. This occurs when blood glucose levels drop, and there is no glucose from food available, leading to the breakdown of protein stores (such as muscle) to replenish blood glucose levels.

Animal proteins have a digestibility of over 90%, while legume proteins have a digestibility of 80%.

Grains and other plants have a digestibility ranging from 60% to 90%, which is lower than animal proteins but can be comparable to legume proteins depending on the specific type.

The key factor in determining protein quality is the essential amino acid content of the protein source.

A complete protein contains all the essential amino acids in amounts sufficient to sustain protein formation in the body.

An incomplete protein lacks some of the essential amino acids necessary for protein synthesis.

Complete proteins include meat, fish, poultry, cheese, eggs, milk, and many soybean products. Quinoa is often considered just short of being a complete protein due to its lysine content.

Incomplete proteins are primarily found in plants such as cereals, beans, nuts, and seeds. They have lower nutritional quality due to:

• Low levels of select essential amino acids (EAA)
• Presence of antinutritional factors like protease inhibitors that decrease protein digestibility.
• Grains lack sufficient lysine.
• Legumes lack enough methionine.

Complementary proteins are formed by combining grains and legumes. This combination ensures that all essential amino acids are present, resulting in a complete protein.

The recommended protein intake for sedentary individuals is 0.8 g/kg BW.

Strength-trained individuals aiming to gain muscle should consume between 1.6 to 1.8 g/kg BW.

Infants up to 6 months old require 2.2 g/kg BW of protein.

Endurance-trained individuals should consume 1.2 to 1.4 g/kg BW of protein.

Children aged 1 to 6 years require 1.2 g/kg BW of protein.

Individuals who are weight-restricted should consume between 1.4 to 1.8 g/kg BW of protein.

A positive nitrogen balance occurs when the body retains more nitrogen than it excretes. This is typically seen in:

1. Growing children
2. Pregnant women
3. Individuals building muscle

Nitrogen equilibrium indicates a state where nitrogen intake equals nitrogen excretion. This is typical for normal healthy individuals.

Potential risks include:

• Contamination: Individual amino acids can be contaminated.
• Interference: They may interfere with the absorption of other essential amino acids (EAA).
• Health Issues: Excess consumption of methionine can worsen symptoms of schizophrenia, promote hardening of the arteries, impair fetal and infant development, and lead to nausea, vomiting, bad breath, and constipation.

Glutamine and branched chain amino acids (BCAAs) may offer some performance benefits in sports, such as:

• Improved Recovery: They may help in muscle recovery post-exercise.
• Reduced Muscle Soreness: BCAAs can reduce muscle soreness after intense workouts.
• Enhanced Endurance: Glutamine may support endurance during prolonged physical activity.

Whey protein is known to enhance the immune system due to its high content of immunoglobulins and lactoferrin, which can help in fighting infections and improving overall immune response.

Whey protein can improve body composition by promoting muscle growth and fat loss, making it beneficial for those looking to enhance their physique or support weight management.

Whey protein may support liver function by providing essential amino acids that aid in the synthesis of proteins necessary for liver health and detoxification processes.

Whey protein can be beneficial for kidney function in healthy individuals, but those with pre-existing kidney conditions should consult a healthcare provider before increasing protein intake.

Some studies suggest that whey protein may exacerbate acne in certain individuals due to its potential to increase insulin levels, which can lead to increased oil production in the skin.

Whey protein may promote gut health by supporting the growth of beneficial gut bacteria and enhancing the gut barrier function, which can improve overall digestive health.

Whey protein can positively impact bone health by providing essential amino acids and promoting the absorption of calcium, which is crucial for maintaining bone density.

The primary objective was to determine the effect of a novel plant-based blend protein (PBP) and PBP with added leucine (PBP + Leu) on aminoacidemia and muscle protein synthesis (MPS) responses in young men and women, hypothesizing that PBP + Leu would stimulate MPS equivalent to whey protein isolate (WHEY).

The MPS increase following ingestion of PBP was less than that following ingestion of PBP + Leu and whey protein, with no significant difference between PBP + Leu and whey protein.

Consumption of PBP isolate with added leucine stimulated muscle protein synthesis to a similar extent as whey protein in young men and women, indicating that PBPs with higher leucine content can promote anabolism comparably to animal-based proteins.

The study employed a randomized, double-blind, crossover design with a primed continuous infusion of L-[ring¹³C₆] phenylalanine administered for 8 hours at each study visit, along with collection of skeletal muscle tissue and blood samples.

False. The body can't store protein, so once needs are met, any extra is used for energy needs or stored as fat. Adding excess protein or amino acids to an adequate diet usually leads to putting on pounds of body fat, not muscle.

Children suffering from kwashiorkor exhibit symptoms such as:

• Swelling in the arms, legs, and stomach area (edema)
• Moon face appearance
• Swollen belly
• Patchy dermatitis due to zinc deficiency
• Wasting of body tissues that is often hidden by swelling

Marasmus is a form of severe malnutrition characterized by a deficiency in both protein and calories. It leads to extreme emaciation, where the body loses significant muscle and fat, resulting in visible ribs and thin limbs. Children suffering from marasmus often appear weak and lethargic.

• High-fat content: Protein-rich foods are often high in saturated fats, which can lead to health issues.
• Colon cancer: Excessive consumption of red meat has been linked to an increased risk of colon cancer.
• Calcium to protein ratio: The ideal ratio is 20:1, but the actual intake is often 9:1, which can affect bone health.
• Dehydration: Excess protein can burden the kidneys to excrete excess nitrogen, requiring more water, which can lead to dehydration, especially in individuals with kidney disease or diabetes.

1. Vegan: Excludes all animal-derived foods
2. Lactovegetarian: Includes milk products
3. Lacto-ovo-vegetarian: Includes milk and eggs
4. Partial vegetarian: Excludes red meat
5. Pesco-vegetarian: Excludes poultry and red meat

• Lower body weight
• Lower blood pressure
• Reduced risk of heart disease
• Lower mortality from cancer, especially colon cancer

Complete proteins are primarily found in animal sources and contain all essential amino acids. Incomplete proteins, found in plant sources, lack one or more essential amino acids. For example:

• Grains: not enough lysine
• Legumes: not enough methionine

Complementary proteins are combinations of different protein sources that together provide all essential amino acids. Examples include:

• Grains & Legumes
• Milk & Grains
• Milk & Legumes

Iron in plant foods is found in legumes, dark green leafy vegetables, iron-fortified cereals, and whole grain breads & cereals. However, this non-heme iron is more poorly absorbed compared to heme iron from animal sources.

Vitamin C enhances the absorption of non-heme iron from plant sources, improving its bioavailability.

The best source of iron is lean red meat, but it can also be found in chicken, turkey, eggs, and cereals.

Iron absorption from a mixed diet that includes meat, fish, and poultry is approximately 14-18%, while absorption from a vegetarian diet is about 5-12%.

• Meat is a rich source of zinc.
• Seafood is also a good source.
• Whole grains, nuts, and legumes provide zinc as well.

Zinc is critical for immune function and growth.

Zinc deficiency in developing countries is often caused by a high intake of cereal protein, which is rich in phytates (an anti-nutrition factor) that makes zinc unavailable for absorption.

Calcium sources include:

• Calcium-fortified juices or soy milk
• Calcium-set tofu
• Navy and white beans
• Almonds
• Tahini
• Chia seeds

Lower oxalate vegetables that are better sources of calcium include:

• Turnip greens
• Broccoli
• Kale

Higher oxalate vegetables, such as spinach, beet greens, and Swiss chard, are less effective sources.

Boiling can reduce oxalate levels in vegetables by 30–87%, making it more effective than steaming or baking.

The primary sources of Vitamin D include:

1. Sunlight exposure - The body produces Vitamin D when exposed to sunlight, although this can be limited in northern climates.

2. Food sources - These include:

   • Fortified milk
   • Cheese
   • Butter
   • Margarine
   • Fish
   • Fortified cereals

3. Supplements - Due to limited sunlight exposure, supplements may be necessary for adequate Vitamin D levels.

Vitamin B12 is primarily found in animal foods such as:

• Eggs
• Milk
• Meat
• Cheese

Additionally, it can be obtained from fortified sources like:

• Soy milk
• Breakfast cereals
• Supplements

The populations at greater risk of nutrient deficiency include:

1. Pregnancy & lactation
2. Infancy
3. Childhood & adolescence