EC

Chapter 6:Protein AA.

CHAPTER 6: PROTEIN - AMINO ACIDS

CHEMIST’S VIEW OF PROTEIN

  • Proteins consist of several fundamental elements:

    • Carbon

    • Hydrogen

    • Oxygen

    • Nitrogen

  • Proteins are organized from amino acids, which are defined by specific functional groups:

    • Carbon ( ext{C})

    • Hydrogen ( ext{H})

    • Amino group (-NH2)

    • Acid group (-COOH)

    • Unique side group or side chain, which varies

  • There are 20 different amino acids, each differing in size, shape, and electrical charge.

AMINO ACIDS

  • Amino Acid Classifications:

    • Nonessential Amino Acids:

    • Can be synthesized in the body.

    • Can be obtained through dietary sources; also termed dispensable.

    • Essential Amino Acids:

    • Cannot be synthesized in sufficient quantities to satisfy bodily needs; known as indispensable.

    • Conditionally Essential Amino Acids:

    • Typically nonessential, but may need to be supplied by dietary sources under certain conditions (e.g., inadequate dietary intake of precursor amino acids).

    • Conditions include inability to convert to the amino acid from its precursor.

AMINO ACIDS

  • Essential Amino Acids:

    • Histidine (HISS-tuh-deen)

    • Isoleucine (eye-so-LOO-seen)

    • Leucine (LOO-seen)

    • Lysine (LYE-seen)

    • Methionine (meh-THIGH-oh-neen)

    • Phenylalanine (fen-il-AL-ah-neen)

    • Threonine (THREE-oh-neen)

    • Tryptophan (TRIP-toe-fan, TRIP-toe-fane)

    • Valine (VAY-leen)

  • Nonessential Amino Acids:

    • Alanine (AL-ah-neen)

    • Arginine (ARJ-ih-neen)

    • Asparagine (ah-SPAR-ah-geen)

    • Aspartic acid (ah-SPAR-tic acid)

    • Cysteine (SIS-teh-een)

    • Glutamic acid (GLU-tam-ic acid)

    • Glutamine (GLU-tah-meen)

    • Glycine (GLY-seen)

    • Proline (PRO-leen)

    • Serine (SEER-een)

    • Tyrosine (TIE-roe-seen)

  • Key Notes:

    • The 20 amino acids listed are prevalent in proteins, while others like taurine and ornithine may exist individually and are not typically incorporated into proteins.

    • Certain amino acids can appear in related forms; for example, proline can gain a hydroxyl group to become hydroxyproline.

EXAMPLES OF AMINO ACIDS

  • Alanine: Structure:

    • H

    • H-C-H

    • C-O-H

    • H-C-H

    • O=C

  • Aspartic Acid: Structure:

    • H

    • H-N-C-C-O-H

    • H

    • H

  • Phenylalanine: Structure not fully illustrated but shares similarities with alanine and aspartic acid.

  • Glycine: Structure:

    • O=C

    • H-N-C-C-O-H

    • H

    • H

PROTEINS: POLYPEPTIDE CHAINS

  • Peptide bonds are critical for linking amino acids, resulting in polypeptide chains composed of 10 or more amino acids.

  • Most proteins typically range in length from 36 to several hundred amino acids.

  • Condensation Reactions:

    • These reactions help connect amino acids by removing a water molecule.

PROTEIN STRUCTURE

  • Primary Structure:

    • Defined as the specific sequence of amino acids linked by peptide bonds (e.g., A-G-V-H-S…).

  • Secondary Structure:

    • Formed by weak electrical attractions within the amino acid chain.

    • Hydrogen bonds attract oxygen, leading to the formation of:

    • Twisted helixes

    • Folded pleats

    • These formations impart strength and rigidity to proteins.

  • Tertiary Structure:

    • Involves polypeptide tangles when long chains twist and fold into complex shapes.

    • Unique side groups of each amino acid either attract or repel from surrounding fluids and other amino acids.

    • Hydrophilic (water-attracting) side groups position themselves at the outer surfaces, while hydrophobic (water-repelling) groups tuck away from water.

    • Tertiary structures maximize stability, leading to various forms such as:

    • Spherical shapes, which store and transport nutrients.

    • Linear structures, exemplified in tendons.

  • Quaternary Structure:

    • Comprises interactions among two or more polypeptide chains forming larger functional complexes.

    • Example: Hemoglobin in red blood cells comprises four polypeptide chains that hold iron and facilitate oxygen transport.

AMINO ACID SEQUENCE OF HUMAN INSULIN

  • Human insulin consists of 51 amino acids arranged in short polypeptide chains.

  • Two disulfide bridges connect these two chains, with a third disulfide bridge spacing a specific section of the chain.

  • Disulfide bridges form between cysteine (Cys) amino acids, which contain sulfur in their side groups.

STRUCTURE OF HEMOGLOBIN

  • The architecture of each polypeptide chain in hemoglobin hinges on the amino acid sequence (primary structure), which twists into a helix (secondary structure) and folds into a globular shape (tertiary structure).

  • Together, four such polypeptide chains constitute the quaternary structure of globular hemoglobin.

  • Heme, the non-protein component, is crucial as it holds iron, enabling oxygen transport.

PROTEIN DENATURATION

  • Denaturation is a process whereby a protein unravels, losing its shape and function due to exposure to various factors such as:

    • Heat

    • Acid

    • Base

    • Agitation

    • Alcohol

  • Examples of denaturation include:

    • Cooked eggs

    • Curdling of milk due to acid

    • Stiffening of whipped egg whites

    • Stomach acid during digestion

PROTEIN DIGESTION IN THE GI TRACT

  • Mouth:

    • Saliva moistens consumed food.

  • Stomach:

    • Hydrochloric acid (HCl) uncoils protein strands and activates stomach enzymes.

    • Pepsin is the primary enzyme responsible for digesting proteins into smaller polypeptides.

  • Small Intestine:

    • Pancreatic and intestinal enzymes (such as trypsin, chymotrypsin, and carboxypeptidase) breakdown polypeptides into much smaller fractions, including tripeptides, dipeptides, and amino acids.

    • Enzymes located on the surface of small intestinal cells (like tripeptidases, dipeptidases, and aminopeptidases) hydrolyze these smaller peptides further into free amino acids.

PROTEIN ABSORPTION

  • Amino acids (AA) are carried by specific transport carriers into intestinal cells.

  • Once inside, AAs may serve as energy sources or be utilized for synthesizing various compounds.

  • Unused AAs are transported to the liver.

  • Whole proteins are typically better processed by the body compared to "predigested" amino acid supplements, as the body deconstructs and absorbs them at an optimal rate suited to physiological needs.

PROTEINS IN THE BODY

  • Humans possess more than 20,000 genes coding for over 100,000 types of proteins.

  • Each gene codes for a specific amino acid sequence, ultimately determining protein functions within the body.

  • The differences in individual proteins contribute to personal uniqueness.

  • A well-balanced diet must provide adequate protein along with an appropriate distribution of essential amino acids to facilitate the production of requisite proteins.

PROTEIN SYNTHESIS

  • The DNA within the nucleus of every cell encompasses the complete code for synthesizing all human proteins.

  • To synthesize a specific protein:

    • Step 1: Transcription

    • The DNA serves as a template for producing messenger RNA (mRNA)

    • The mRNA then transports the genetic code from the nucleus into the cytoplasm, where it binds to a ribosome (the protein synthesis factory).

    • Step 2: Translation

    • The mRNA sequence directs the order of amino acids needed to construct the protein.

    • mRNA recruits transfer RNA (tRNA) to ferry amino acids from the cell fluid to facilitate protein synthesis.

    • After the completion of synthesis, the newly formed protein strand is released.

SEQUENCING ERRORS

  • Any errors in the amino acid sequencing can lead to altered proteins.

  • Example:

    • In sickle cell disease, valine replaces glutamic acid in the sequence of two hemoglobin polypeptide chains.

    • This substitution results in sickle-shaped erythrocytes (RBCs) which impair hemoglobin's capacity to transport oxygen.

PROTEIN FUNCTIONS IN THE BODY

TABLE 6-3 Protein Functions in the Body

  • Structural materials:

    • Proteins contribute significantly to the composition of most body tissues, providing strength and structural form to muscles, organs, bones, tendons, etc.

  • Enzymes:

    • Catalyze biochemical reactions without being altered by the reaction itself.

  • Hormones:

    • Proteins regulate various bodily processes (not all hormones are proteins, however).

  • Fluid balance:

    • Maintain appropriate bodily fluid volume and composition.

  • Acid-base balance:

    • Act as buffers to sustain stable pH levels in body fluids.

  • Transportation:

    • Proteins facilitate the conveyance of substances like lipids, vitamins, minerals, and oxygen throughout the body.

  • Antibodies:

    • Proteins play a critical role in defending against foreign invaders, thereby protecting the body from diseases.

  • Energy and glucose:

    • Proteins provide essential fuel and can also contribute glucose when necessary.

    • Other protein applications include roles in clotting (fibrin), scarring (collagen), and vision (opsin).

ROLES OF PROTEINS: STRUCTURAL MATERIALS

  • Proteins serve as building blocks for most body structures, contributing material for ligaments and tendons, formations between cells of artery walls, and creating the collagen matrix found in bones and teeth.

  • Facilitate the turnover of cells by replacing dead or damaged cells with new protein-rich cells.

  • Form important structures like hair and nails, along with muscle cells and GI tract cells.

ROLES OF PROTEINS: ENZYMES

  • Enzymes are specialized proteins that assist in facilitating chemical reactions without undergoing any alteration during the process, effectively acting as protein catalysts.

  • They play vital roles in breaking down, building up, and transforming various substances.

ROLES OF PROTEINS: HORMONES

  • Certain hormones consist of proteins, functioning as messenger molecules released from endocrine glands dispatched by blood to purpose-driven tissues.

ROLES OF PROTEINS: FLUID BALANCE

  • Proteins are critical for regulating fluid balance by attracting water, ensuring that bodily fluids remain in appropriate compartments.

  • In cases of critical illness or protein malnutrition, plasma proteins may leak from capillaries, leading to fluid accumulation in tissues (edema).

  • Potential causes for this imbalance include:

    • Excess protein loss resulting from inflammation.

    • Inadequate protein synthesis stemming from liver disease.

    • Insufficient dietary protein intake.

ROLES OF PROTEINS: TRANSPORT PROTEINS

  • Transport proteins carry nutritional substances and other molecules throughout body fluids.

    • Example: Hemoglobin acts as a transport protein, conveying oxygen from the lungs to cells.

  • Certain transport proteins are embedded within cell membranes, operating as pumps that bind to specific compounds and release them on the opposite side of the membrane.

    • Each transport protein has specificity towards particular compounds or groups of compounds.

MORE PROTEIN ROLES

  • Acid–Base Regulators:

    • Act as buffers to maintain a constant pH level by modulating hydrogen ion concentration in body fluids.

  • Antibodies:

    • Serve as defense mechanisms against diseases, detecting and neutralizing antigens (viruses, bacteria, toxins) through the production of antibodies.

    • The body has a memory for rapid antibody production upon subsequent exposures, facilitating immunity.

  • Energy and Glucose:

    • Proteins can contribute approximately 10-15% of total energy needs, a proportion that elevates when overall energy intake is restricted.

    • In cases of inadequate dietary carbohydrate, the body can generate glucose from dietary or body amino acids, which is crucial for red blood cells and brain activity.

    • Prolonged fasting or starvation can result in the wastage of lean tissue.

    • It's critical to adhere to a balanced diet optimal for bodily functions.

  • Storage Role:

    • Excess protein may be converted to glucose (gluconeogenesis) for glycogen storage or into ketone bodies for fat storage.

  • Other Roles:

    • Blood clotting facilitated by fibrin – proteins that form fibers involved in the clotting process.

    • Vision assisted by opsin – the protein pigment found in the retina that detects light.

PROTEIN METABOLISM

  • Protein Turnover:

    • The continuous production and breakdown of proteins in the body.

    • The degradation of body proteins releases amino acids.

    • Breakdown of dietary proteins yields amino acids from the food consumed.

    • These dietary and body amino acids contribute to the amino acid pool found within cells and blood, available for significant functions such as generating new proteins, nitrogen-containing compounds, or converting into glucose or energy.

PROTEIN METABOLISM: NITROGEN BALANCE

  • Refers to the ratio of nitrogen taken in versus the nitrogen expelled from the body.

  • Healthy Adults:

    • Generally, dietary protein intake balances nitrogen excretion through urine, feces, and sweat leading to nitrogen equilibrium, also known as zero nitrogen balance.

  • Special Conditions:

    • Infants, children, adolescents, pregnant women, and individuals recovering from protein deficiency or illness may experience positive nitrogen balance, where nitrogen intake exceeds nitrogen excretion as new tissues are synthesized.

    • Conversely, during periods of starvation, burns, illnesses, infections, or fever, the body may enter a negative nitrogen balance when muscle and body proteins are catabolized for energy or glucose, leading to overall protein loss.

PRODUCTION OF PROTEINS AND NONESSENTIAL AMINO ACIDS

  • Cells have the capability to assemble amino acids into proteins.

  • If an essential amino acid is deficient, the body can degrade lean tissue to procure it.

  • If a nonessential amino acid is lacking:

    • The cells can synthesize it from a keto acid by incorporating available nitrogen.

    • Transamination reactions in the liver entail the transfer of an amino group from one amino acid to a keto acid, ultimately creating a new nonessential amino acid alongside a new keto acid.

TRANSAMINATION AND SYNTHESIS OF AMINO ACIDS

  • In transamination, amino groups (NH2) are exchanged between amino acids and keto acids, generating a new nonessential amino acid and an alternate keto acid.

  • These reactions necessitate the involvement of vitamin B6 as a coenzyme.

OTHER AMINO ACID USES

  • Amino acids contribute to the synthesis of various compounds:

    • Tyrosine and Tryptophan:

    • Serve as precursors for neurotransmitters, essential for transmitting messages across the nervous system.

    • Tyrosine contributes to melanin production (pigment in skin, hair, and eyes) and thyroxine (a hormone regulating metabolic rate).

    • Tryptophan is a precursor for niacin (vitamin) and serotonin (neurotransmitter important for sleep, appetite regulation, and sensory perception).

  • Energy and Glucose Source:

    • Proteins comprise approximately 10 to 15% of energy requirements, a figure likely to rise when overall energy intake is restricted.

    • Glucose can be synthesized from amino acids if carbohydrate intake is insufficient, especially critical for red blood cells and brain metabolism.

    • Prolonged fasting leads to lean tissue loss, hence the importance of a balanced diet for optimal health.

    • Excess proteins can either convert into glucose (gluconeogenesis) for glycogen storage or into ketone bodies for fat storage.

DEAMINATION OF AMINO ACIDS

  • Deamination pertains to the removal of the nitrogen-containing amino group from an amino acid.

  • This process occurs when amino acids are catabolized for energy or to fabricate glucose or ketone bodies.

  • The two primary byproducts of deamination are:

    • Ammonia (NH3): A toxic substance.

    • Carbon structure without an amino group (keto acid): Can enter metabolic pathways for energy production, the synthesis of nonessential amino acids, or convert into glucose, ketone bodies, and fats.

UREA SYNTHESIS

  • Ammonia is produced during the deamination of amino acids.

  • The liver detoxifies ammonia by incorporating it with carbon dioxide (CO2) to yield urea.

  • Urea production increases in response to higher protein intake.

EXCRETING UREA

  • The liver is responsible for urea production and releases it into the bloodstream.

  • The kidneys filter urea from the blood for elimination via urine.

  • Health Considerations:

    • Elevated blood ammonia levels may indicate liver disease.

    • Elevated blood urea levels could signify kidney disease.

    • Note: High-protein diets (exceeding 100 grams per day) necessitate higher water intake to effectively dilute and excrete urea through urine.

PROTEIN QUALITY FACTORS

  • High-Quality Proteins:

    • Dietary proteins that include all the essential amino acids in proportions suitable for human requirements.

  • Reference Protein:

    • Established standard against which other proteins' quality is compared.

  • Factors Affecting Protein Quality:

    • Digestibility:

    • The efficiency of amino acid absorption from specific proteins.

      • Animal proteins: 90-99% digestible.

      • Plant proteins: 70-90% digestible.

      • Legumes and soy over 90% digestibility.

    • Amino Acid Composition:

    • High-quality proteins contain at least nine essential acids along with adequate nitrogen-containing amino groups for synthesizing nonessential amino acids.

    • Limiting Amino Acids:

    • The essential amino acid that is found in the least amounts in a food relative to biological needs, likely includes lysine, methionine, threonine, and tryptophan.

COMPLEMENTARY PROTEINS

  • Involves the combination of two or more dietary proteins where the amino acid profiles complement each other, ensuring that missing essential amino acids in one source are fulfilled by another.

  • For instance, legumes provide isoleucine and lysine but are low in methionine and tryptophan; grains supply methionine and tryptophan but lack isoleucine and lysine.

  • Eating complementary plant proteins throughout the day suffices to meet essential amino acid requirements, dispelling the myth that they need to be consumed within the same meal.

HEALTH EFFECTS OF PROTEIN

Protein Deficiency

  • Occurs when dietary intake consistently lacks sufficient protein or essential amino acids, potentially leading to:

    • Stunted growth

    • Impaired brain and kidney functionality

    • Poor immune response

    • Insufficient nutrient absorption

cardiovascular diseases

  • Linked to high-protein diets, particularly those rich in saturated fats derived from animal sources.

  • Mitigation strategies include replacing high saturated fat proteins with plant proteins (such as legumes/nuts), poultry, and fish to lower risk.

Cancer

  • Although protein itself does not appear to elevate cancer risk, certain protein sources (like processed and red meats) are regarded as carcinogenic.

  • Conversely, soy and legumes may confer protective benefits against cancer risk.

Adult Bone Loss (Osteoporosis)

  • Some evidence suggests that high protein consumption can intensify calcium excretion, posing risks for osteoporosis.

Weight Control

  • Foods high in protein promote satiety, potentially aiding in weight management strategies.

Kidney Disease

  • High protein intake raises the workload on kidneys, necessitating increased water consumption.

  • Excessive intake may accelerate deterioration in individuals with chronic kidney disease.

RECOMMENDED INTAKES

  • Dietary protein is essential as it provides the only source of essential amino acids and contributes the only practical source of nitrogen for constructing nonessential amino acids.

  • A balanced protein intake should constitute 10% to 35% of daily energy consumption.

  • RDA for Adults:

  • Calculated as 0.8 g/kg of body weight per day, assuming that the diet delivers adequate carbs and fats for energy requirements.

  • To calculate protein requirements:

    • Convert weight in pounds to kilograms (divide the weight by 2.2).

    • Multiply the weight in kilograms by 0.8 grams.

FROM GUIDELINES TO GROCERIES

  • Protein Food Sources:

    • A general rule is that one ounce of most protein-rich foods delivers around seven grams of protein.

    • The USDA Food Patterns recommend incorporating a variety of protein sources.

  • Dairy Products:

    • A serving of milk or yogurt offers approximately 8 grams of protein.

  • Vegetables and Grains:

    • They generally yield about 2-3 grams of protein per serving.

    • Consumers are advised to check food labels to obtain protein content data.

  • It has been observed that current protein intakes in the United States frequently exceed necessary amounts.

  • Prioritize moderation along with healthful options when consuming protein sources.

PROTEIN AND AMINO ACID SUPPLEMENTS

  • Protein Powders:

    • Widely consumed by athletes post-exercise to enhance muscle strength and encourage protein synthesis.

  • Convenience and Cost:

    • Whey protein, a by-product of cheese processing, is notably popular.

  • Amino Acid Supplements:

    • Do not inherently appear in foods; potential risks of excessive intake include:

    • Digestive distress (like diarrhea).

    • Toxicity and deficiency can arise due to competition for absorption among amino acids.

serve as energy sources or be utilized for synthesizing various compounds. Unused amino acids are transported to the liver. Whole proteins are generally better processed by the body compared to "predigested" amino acid supplements because the body deconstructs and absorbs them at an optimal rate tailored to physiological needs.

6.3 How the Body Makes Proteins and Uses Them to Perform Various Roles

Protein Synthesis

The DNA within the nucleus of every cell contains the complete genetic code for synthesizing all human proteins. The process involves two main steps:

  1. Transcription: DNA acts as a template to produce messenger RNA (mRNA). The mRNA carries the genetic code from the nucleus to the cytoplasm, where it attaches to a ribosome.

  2. Translation: The mRNA sequence dictates the specific order of amino acids needed to build the protein. Transfer RNA (tRNA) molecules transport the appropriate amino acids from the cell fluid to the ribosome to facilitate protein synthesis. Once the protein strand is complete, it is released.

Sequencing Errors

Any errors in the amino acid sequence can result in altered proteins. For example, in sickle cell disease, valine replaces glutamic acid in hemoglobin, leading to sickle-shaped red blood cells that impair oxygen transport.

Protein Functions in the Body

Proteins perform a multitude of vital roles:

  • Structural Materials: They form the building blocks for most body tissues, including muscles, organs, bones, tendons, ligaments, hair, and nails. They also facilitate cell turnover by replacing damaged or dead cells.

  • Enzymes: Specialized proteins that act as catalysts for biochemical reactions, breaking down, building up, and transforming substances without being altered themselves.

  • Hormones: Some hormones (messenger molecules) are proteins that regulate various bodily processes, released from endocrine glands and transported to target tissues.

  • Fluid Balance: Proteins help regulate fluid volume and composition by attracting water, preventing fluid accumulation (edema) in tissues, which can occur with protein malnutrition or critical illness.

  • Acid-Base Balance: They act as buffers to maintain a stable pH level in body fluids by modulating hydrogen ion concentration.

  • Transportation: Proteins carry vital substances throughout the body (e.g., hemoglobin transports oxygen) and function as pumps within cell membranes to move compounds across.

  • Antibodies: Critical components of the immune system, defending against foreign invaders (antigens) like viruses, bacteria, and toxins.

  • Energy and Glucose: Proteins can contribute approximately 10-15% of total energy needs, and in situations of inadequate carbohydrate intake, amino acids can be converted into glucose (gluconeogenesis), essential for brain and red blood cell function.

  • Other Roles: Involved in blood clotting (fibrin) and vision (opsin).

6.4 Differences Between High-Quality and Low-Quality Proteins

Protein Quality Factors

  • High-Quality Proteins: Dietary proteins that provide all nine essential amino acids in proportions suitable for human needs. They also supply adequate nitrogen for synthesizing nonessential amino acids.

    • Reference Protein: An established standard used for comparing the quality of other proteins.

    • Digestibility: High-quality proteins are efficiently absorbed.

      • Animal proteins: 90-99% digestible.

      • Plant proteins: 70-90% digestible (legumes and soy over 90%).

  • Low-Quality Proteins: Proteins that are deficient in one or more essential amino acids, or have lower digestibility.

    • Limiting Amino Acids: The essential amino acid present in the smallest quantity relative to the body's needs in a particular food. Common limiting amino acids include lysine, methionine, threonine, and tryptophan.

Complementary Proteins

This strategy involves combining two or more plant-based dietary proteins whose amino acid profiles complement each other, ensuring that the essential amino acids missing in one source are supplied by another. For instance, legumes are rich in isoleucine and lysine but low in methionine and tryptophan, while grains provide methionine and tryptophan but lack isoleucine and lysine. Consuming a variety of complementary plant proteins throughout the day is sufficient to meet essential amino acid requirements, without needing to consume them in the same meal.

6.5 Health Benefits of, and Recommendations for, Protein

Health Benefits of Protein

  • Weight Control: High-protein foods promote satiety, which can assist in weight management.

  • Structural Support: Provides the fundamental building blocks for muscles, organs, skin, hair, and nails, and supports the continuous repair and replacement of cells.

  • Enzyme and Hormone Production: Essential for synthesizing enzymes that catalyze reactions and protein-based hormones that regulate bodily functions.

  • Immune Function: Crucial for producing antibodies, which are vital for defending the body against diseases.

Health Considerations (Risks of Imbalance)

  • Protein Deficiency: Can lead to stunted growth, impaired brain and kidney function, poor immune response, and insufficient nutrient absorption.

  • Cardiovascular Diseases: Diets high in saturated fat from animal protein sources can increase risk. Replacing these with plant proteins, poultry, and fish can mitigate this.

  • Cancer: While protein itself isn't a direct cause, processed and red meats are considered carcinogenic. Soy and legumes may offer protective benefits.

  • Adult Bone Loss (Osteoporosis): Some evidence suggests high protein consumption may increase calcium excretion, potentially impacting bone health.

  • Kidney Disease: High protein intake increases the workload on kidneys, necessitating higher water consumption and potentially accelerating deterioration in individuals with pre-existing chronic kidney disease.

Recommended Intakes

  • Daily Energy Consumption: A balanced protein intake should constitute 10% to 35% of daily energy consumption.

  • RDA for Adults: $0.8 \text{ g/kg}$ of body weight per day, assuming adequate carbohydrate and fat intake for energy.

    • Calculation: Convert weight in pounds to kilograms (divide by 2.2), then multiply by 0.8 \text{ grams}.

  • Food Sources: One ounce of most protein-rich foods provides approximately seven grams of protein. USDA Food Patterns recommend a variety of sources.

    • Dairy products (milk, yogurt): 8 grams of protein per serving.

    • Vegetables and Grains: Typically 2-3 grams of protein per serving.

  • Current Intake: Protein intake in the United States often exceeds necessary amounts. Prioritize moderation and healthful options.