Chapter 6

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Questions and Answers

What is the primary role of protein in the human body?

Muscle and tissue repair (correct)

Carbohydrate metabolism

Fat storage

Energy production

Which component is unique to protein compared to carbohydrates and fats?

Carbon

Nitrogen (correct)

Hydrogen

Oxygen

What are the building blocks of proteins?

Monosaccharides

Amino acids (correct)

Nucleotides

Fatty acids

How many amino acids are required by the human body?

20 Signup and view all the answers

Which of the following is NOT a function of protein in the body?

Energy storage Signup and view all the answers

What are the five components of amino acid structure?

Central carbon, carboxyl group, hydrogen, amino group, side chain Signup and view all the answers

In what ways can protein intake be optimized throughout the day?

Distributing protein intake evenly across meals Signup and view all the answers

What percentage of bodily tissues, excluding water, is protein?

Around 50% Signup and view all the answers

What happens to amino acids during a dehydration synthesis reaction?

They form peptide bonds and release water. Signup and view all the answers

What is the role of pepsin in protein digestion?

It begins the breakdown of proteins into smaller peptides. Signup and view all the answers

During which process is water added to break down a peptide bond?

Hydrolysis Signup and view all the answers

What does the hormone gastrin do in the digestive process?

Stimulates the release of digestive fluids. Signup and view all the answers

What is a dipeptide?

A chain of two amino acids. Signup and view all the answers

What initiates the denaturation of proteins in the stomach?

Hydrochloric acid Signup and view all the answers

How many amino acids must typically be present in a protein to be classified as a polypeptide?

Ten or more Signup and view all the answers

What is the main function of cholecystokinin in the digestive process?

Stimulates bile production in the liver. Signup and view all the answers

Which protein is known for providing elasticity in muscles?

Titin Signup and view all the answers

What is a characteristic of the process of denaturation?

It alters protein shape without affecting primary structure. Signup and view all the answers

What occurs during the process of protein synthesis?

Amino acids are joined to form proteins. Signup and view all the answers

What is the primary role of the pancreas in protein digestion?

Secretes protease enzymes into the small intestine. Signup and view all the answers

Which of the following statements about myosin is correct?

It uses ATP to facilitate muscle contraction. Signup and view all the answers

What characterizes essential amino acids (EAAs)?

They must be consumed in the diet. Signup and view all the answers

Which amino acids are classified as conditionally essential?

Arginine and Cysteine Signup and view all the answers

What process generates glucose from non-carbohydrate carbon substrates?

Gluconeogenesis Signup and view all the answers

Which amino acid is NOT typically essential under normal circumstances?

Serine Signup and view all the answers

What defines nonessential amino acids?

They can be synthesized by the body. Signup and view all the answers

Which branched chain amino acids are important for skeletal muscle tissue?

Leucine, Isoleucine, Valine Signup and view all the answers

What is the primary role of cell signaling?

To govern cellular functions. Signup and view all the answers

What distinguishes glucogenic amino acids from ketogenic amino acids?

Ketogenic amino acids can be converted to ketone bodies. Signup and view all the answers

Which of the following amino acids is both glucogenic and ketogenic?

Threonine Signup and view all the answers

Why are conditionally essential amino acids significant during certain physiological conditions?

They must be consumed when needed. Signup and view all the answers

What is a characteristic of dehydration synthesis during protein synthesis?

Water is produced. Signup and view all the answers

Which type of amino acid does not typically need to be consumed in the diet?

Nonessential amino acids Signup and view all the answers

What mnemonic can help remember the essential amino acids?

PVT TIM HALL Signup and view all the answers

What is the role of amino acids in energy metabolism during negative energy balance?

They are broken down preferentially over fatty acids. Signup and view all the answers

What is the primary function of collagen in the human body?

To provide structural integrity Signup and view all the answers

Which macronutrient is primarily structural and functional, rather than mainly serving as an energy source?

Proteins Signup and view all the answers

What enzyme is specifically mentioned as involved in the metabolism of glucose?

Pyruvate dehydrogenase Signup and view all the answers

What is the role of the sodium-potassium pump in human cells?

To create a gradient for electrical signaling Signup and view all the answers

What percentage of animal protein is typically absorbed by the body?

95% Signup and view all the answers

Which of the following proteins is found in hair and nails?

Keratin Signup and view all the answers

What substance transports blood from the spleen and stomach to the liver?

Hepatic portal vein Signup and view all the answers

What type of enzymes cleave individual amino acids from a peptide chain?

Aminopeptidases Signup and view all the answers

Which of the following proteins provides elasticity to tissues?

Elastin Signup and view all the answers

Which animal protein is known to have a higher absorption rate compared to plant protein?

Cottage cheese Signup and view all the answers

What is the main storage form of carbohydrates in the body?

Glycogen Signup and view all the answers

What happens to proteins and peptides that escape the small intestine and reach the large intestine?

They are fermented by bacteria Signup and view all the answers

Which protein is crucial for transporting oxygen and carbon dioxide in blood?

Hemoglobin Signup and view all the answers

What constitutes the main physical structure of muscles and bones in the body?

Proteins Signup and view all the answers

What is the recommended range of protein intake in grams per kilogram of body weight for optimal nutrition?

1.2 to 2.2 grams Signup and view all the answers

What is NOT considered an advanced strategy for optimizing protein intake?

Limiting protein to one meal per day Signup and view all the answers

Which statement about amino acids is correct?

Essential amino acids cannot be synthesized by the body. Signup and view all the answers

Which of the following is a method to maximize muscle protein synthesis (MPS)?

Distributing protein intake evenly throughout the day Signup and view all the answers

What is the primary function of the body's digestion and absorption of dietary protein?

To convert dietary protein into amino acids Signup and view all the answers

What did cyclists report during the normal protein treatment compared to the high-protein treatment?

More symptoms of upper respiratory tract infection Signup and view all the answers

What is the recommended dietary allowance (RDA) for protein for men?

56 grams per day Signup and view all the answers

What is the general recommendation for protein intake based on activity level?

0.8 to 2.2 grams per kilogram of bodyweight Signup and view all the answers

Why do the USDA guidelines not modify protein intake based on individual need?

They are only based on average recommendations Signup and view all the answers

What essential bodily function do lipoproteins perform?

Transporting lipids between tissues for metabolism or storage Signup and view all the answers

What is one reason the RDA may appear dramatically less than the USDA guidelines?

It is based on sedentary individuals only Signup and view all the answers

Which protein is primarily responsible for maintaining fluid balance in the bloodstream?

Albumin Signup and view all the answers

How much protein is suggested for sedentary persons based on recent evidence?

0.8 grams per kilogram of bodyweight Signup and view all the answers

What role do amino acids play when their levels increase in the body?

Signaling muscle cells to begin protein synthesis Signup and view all the answers

How often are the dietary guidelines for Americans revised?

Every 5 years Signup and view all the answers

What percentage of daily calories is suggested to come from protein sources in some dietary guidelines?

20 to 25% Signup and view all the answers

How do proteins contribute to the body's pH balance?

By binding to free hydrogen ions or hydroxyl groups Signup and view all the answers

What characteristic might require an individual to need more protein?

Engaging in high-intensity exercise Signup and view all the answers

What is the primary functional role of hemoglobin in the body?

Binding oxygen for transport in red blood cells Signup and view all the answers

Which peptide hormone stimulates the release of breast milk post-birth?

Oxytocin Signup and view all the answers

What determines the total daily protein requirement for an individual?

Exercise frequency and type Signup and view all the answers

What is a primary function of antibodies produced by white blood cells?

To protect the body from infections Signup and view all the answers

What is a plausible maximum protein intake goal even for sedentary individuals?

2.2 grams per kilogram of body weight Signup and view all the answers

What dietary need increases for athletes compared to non-athletes?

Protein intake for muscle repair Signup and view all the answers

What is a primary focus of the Recommended Dietary Allowance (RDA)?

Avoiding adverse health effects Signup and view all the answers

What kind of studies mostly inform the Institute of Medicine recommendations for protein?

Nitrogen balance studies Signup and view all the answers

What is the total concentration of blood pH considered to be slightly alkaline?

7.4 Signup and view all the answers

What is a characteristic of neurotransmitters in comparison to hormones?

They are quicker in action and part of the nervous system Signup and view all the answers

What might the body struggle with if amino acids were insufficient?

Fighting off infections Signup and view all the answers

What is one consequence of a high-protein diet for trained athletes?

Potential stress on the immune system Signup and view all the answers

What is a function of leucine in a high-protein diet?

It enhances muscle hypertrophy when combined with other amino acids Signup and view all the answers

What common misconception exists about dietary protein requirements?

Only athletes need increased protein intake Signup and view all the answers

What is the recommended protein intake for individuals engaged in vigorous resistance training?

1.7 to 2.2 g/kg body weight Signup and view all the answers

What is the term used for proteins that contain all essential amino acids in sufficient quantities?

Complete proteins Signup and view all the answers

Which factor may lead to decreased effectiveness of dietary protein in older adults?

Anabolic resistance Signup and view all the answers

What combination of foods is an example of complementary proteins?

Rice and beans Signup and view all the answers

In terms of protein intake during a weight loss regimen, which amount is typically recommended for maintaining muscle mass?

1.8 to 2.2 g/kg body weight Signup and view all the answers

What can be a consequence of consuming protein snacks that are high in sugar and fat?

Counterproductive to fat loss Signup and view all the answers

For athletes experiencing high training demands, what adjustment is recommended for protein intake?

Increase protein in relation to calorie intake Signup and view all the answers

Which protein source is considered a complete protein?

Soy Signup and view all the answers

What is a significant aspect of protein quality?

The number of essential amino acids and digestibility Signup and view all the answers

How should protein recommendations be presented to clients effectively?

Broadly, allowing personal decisions Signup and view all the answers

What is a common occurrence when individuals follow calorie-restricted diets?

Loss of both muscle and fat Signup and view all the answers

Which protein intake is considered optimal for aging individuals to maintain muscle mass?

1.2 to 1.6 g/kg body weight Signup and view all the answers

What is the main purpose of consuming complementary proteins in a diet?

To obtain a complete amino acid profile Signup and view all the answers

What is the main role of leucine in protein synthesis?

To increase muscle protein synthesis Signup and view all the answers

How often should protein be consumed to maximize net muscle protein synthesis?

Every 3 hours Signup and view all the answers

Which of the following best describes a complete protein?

A protein containing sufficient quantities of all essential amino acids Signup and view all the answers

What is protein pacing?

Having six meals a day with a specific percentage of daily calories from protein Signup and view all the answers

What is the optimal dose of leucine per kilogram of body weight to maximize protein synthesis?

0.05 grams Signup and view all the answers

According to the research on protein distribution, how does even distribution of protein affect muscle synthesis?

It results in greater rates of muscle protein synthesis Signup and view all the answers

When is consuming protein during exercise particularly important?

For endurance events lasting longer than 3 to 4 hours Signup and view all the answers

Which protein source has the highest percentage of protein as leucine?

Whey Supplement Signup and view all the answers

Why might protein timing strategies be beneficial for athletes?

They support the theoretical improvements in physiological adaptations Signup and view all the answers

What is a key finding regarding protein intake and muscle mass maintenance during calorie restriction?

Consuming higher protein percentages can enhance fat loss and maintain muscle mass Signup and view all the answers

What can be inferred about the role of all amino acids in the formation of proteins?

All amino acids are equally important for protein formation Signup and view all the answers

What is the effect of consuming protein prior to exercise?

It attenuates rates of muscle catabolism Signup and view all the answers

What does the quality of protein depend on?

Quantity of essential amino acids and digestibility Signup and view all the answers

Which meal strategy showed superior muscle protein synthesis in a study?

Four servings of 20 grams of whey protein Signup and view all the answers

What carbohydrate to protein ratio is often recommended to enhance muscle glycogen replenishment after a workout?

3:1 Signup and view all the answers

How does the timing of protein consumption affect muscle protein synthesis (MPS) in well-trained individuals after resistance training?

It further enhances MPS rates. Signup and view all the answers

What is the effect of consuming a minimal protein amount per meal on achieving the anabolic threshold?

It does not reach the anabolic threshold. Signup and view all the answers

What is one common misconception about post-workout protein consumption?

It is crucial for muscle growth. Signup and view all the answers

What might happen if protein intake is increased post-workout over the total daily protein intake?

Muscle growth may be enhanced. Signup and view all the answers

How many meals should a person ideally consume to maintain the anabolic threshold throughout the day?

4 meals per day Signup and view all the answers

What role does leucine play in muscle protein synthesis?

It signals for muscle protein synthesis. Signup and view all the answers

What have investigations shown regarding muscle protein synthesis rates immediately after resistance training?

They increase when protein is consumed afterward. Signup and view all the answers

What is one takeaway regarding protein intake for endurance athletes training multiple times a day?

Focus should be on total daily protein intake. Signup and view all the answers

What threshold is referenced in the context of muscle protein synthesis?

The anabolic threshold. Signup and view all the answers

What did a meta-analysis of multiple studies reveal about post-workout protein consumption?

It has no statistically significant effect on muscle gain when total daily intake is controlled. Signup and view all the answers

Why do myths regarding protein consumption emerge in nutrition science?

Due to insufficient research. Signup and view all the answers

What happens to amino acid concentration after three hours post-meal?

It drops. Signup and view all the answers

What is a potential consequence of reaching the anabolic threshold only part of the day?

Muscle protein synthesis may be impaired. Signup and view all the answers

Study Notes

Protein Structure

Protein is essential for human life, involved in numerous bodily functions
Protein is composed of the elements carbon, hydrogen, oxygen, and nitrogen
The building blocks of protein are amino acids
There are 20 amino acids required for human bodily functions
Each amino acid has a central carbon, a carboxyl group, a hydrogen, an amino group, and a side chain (R group)
The side chain makes each amino acid unique
Essential amino acids (EAAs) must be obtained through diet because they cannot be synthesized by the body
There are nine EAAs, including three branched-chain amino acids (BCAAs): leucine, isoleucine, and valine
Conditionally essential amino acids are not typically essential but can become essential in certain physiological conditions
Nonessential amino acids can be synthesized by the body from other amino acids
Amino acids can be classified as glucogenic, ketogenic, or both based on their potential to become glucose or ketones for energy metabolism

Protein Synthesis

Proteins are broken down into amino acids during digestion and absorbed in the intestines
Amino acids are then transported to peripheral tissues and recombined to form new proteins
Protein synthesis is the process of joining amino acids together to form proteins
Amino acids are bonded together by dehydration synthesis, where water is removed
Hydrolysis is the opposite of dehydration synthesis, occurring during digestion when proteins are broken down into amino acids
A dipeptide is formed when two amino acids are joined
Three amino acids joined together form a tripeptide
Four to nine amino acids joined together form an oligopeptide
Polypeptides are chains of 10 or more amino acids
The human body is constantly in a state of protein synthesis (anabolic) and protein breakdown (catabolic)
Muscle protein synthesis is greater than breakdown when gaining muscle mass
Muscle protein breakdown is greater than synthesis during inactivity

Protein Digestion, Absorption, and Function

Protein digestion begins with denaturation, changing the shape of a protein but not its primary structure
Denaturation occurs in response to factors such as temperature, pH, and enzymes
Cooking denatures proteins
Chewing food stimulates the release of gastrin, which causes the release of hydrochloric acid and pepsinogen in the stomach
Pepsinogen is converted into pepsin by hydrochloric acid, which begins breaking down proteins in the stomach
Smaller peptide chains move from the stomach to the small intestine
Secretin and cholecystokinin, released by intestinal cells, stimulate the pancreas to release protease enzymes into the small intestine
Protease enzymes further break down proteins
Peptidases and aminopeptidases break down peptide chains into individual amino acids and dipeptides, which are absorbed in the small intestine
Amino acids are transported to the liver via the hepatic portal vein
About 85% of plant protein and 95% of animal protein is absorbed
Remaining proteins and peptides are fermented by bacteria in the large intestine and secreted as waste

Protein Function

Protein is a structural and functional macronutrient, forming bodily structures and serving various functions
Protein can be metabolized for energy, but this occurs mainly when there is an abundance of protein and/or insufficient carbohydrate
Protein is primarily used to create bodily tissues, enzymes, cellular transporters, hormones, and neurotransmitters, maintain fluid balance, buffer acids and bases, and support the immune system
Most bodily protein is located in the musculoskeletal system
Collagen, a strong protein found in bones, skin, tendons, ligaments, and joints, provides structural integrity
Elastin, another protein, provides elasticity to tissues
Myosin, actin, and titin are muscle proteins that enable movement
Keratin is a tough protein found in hair and fingernails
Nearly all enzymes are made from protein
Enzymes catalyze chemical reactions and are essential for various bodily functions, including digestion and metabolism
Cellular transporters are similar to enzymes but act as doorways in cell membranes, facilitating transport across cell membranes
The sodium-potassium pump, an important cellular transporter, actively transports ions across cell membranes, contributing to electrical signaling
Proteins are also important for transporting nutrients throughout the body

Protein Functions

Hemoglobin is a protein in red blood cells that transports both oxygen and carbon dioxide.
Lipoproteins transport lipids (fats) throughout the body, including cholesterol.
The Sodium–Potassium Pump is a protein on the cell membrane that transports sodium and potassium to create electrochemical gradients.
Proteins can act as cellular receptors that respond to stimuli outside the cell and relay a message inside the cell.
Proteins help maintain fluid balance by transporting water across cell membranes and by creating a concentration gradient that helps pull excess fluid from tissues back into the bloodstream.
Proteins regulate the body's acid-base balance by binding to hydroxyl groups or hydrogen ions in the blood.
Hemoglobin helps with pH balance by preventing carbon dioxide from forming carbonic acid.

Protein Hormones and Neurotransmitters

Peptide hormones are derived from amino acids.
Examples of peptide hormones include human growth hormone, insulin, gastrin, and leptin.
Peptide hormones can also act as neurotransmitters.
Examples of peptides that function as neurotransmitters include oxytocin, epinephrine, glutamate, dopamine, serotonin, and histamine.

Protein and the Immune System

White blood cells use proteins to fight infection and disease.
In response to infection, white blood cells produce antibodies, which are proteins, to protect the body from sickness.

Dietary Protein Needs

Non-athletes need protein for a variety of health functions.
Active exercisers and athletes need additional protein for muscle repair and recovery.
Athletes who train with high volume or intensity may require more protein than those who train with less volume or intensity.
Older adults may need more protein to maintain or increase lean muscle mass.

Protein Recommendations

The USDA dietary guidelines recommend 85-90 grams of protein per 2,000 calories per day (17-18% of total calories).
The RDA for protein is 46 grams per day for women and 56 grams per day for men (0.8 grams per kilogram of bodyweight per day).
Individuals need between 0.8 to 2.2 grams of protein per kilogram of bodyweight per day.

Protein Quality

Protein quality refers to the number of essential amino acids and the digestibility of a protein-containing food.
Complete proteins contain all essential amino acids in sufficient quantities.
Animal proteins are generally complete proteins, while plant proteins are generally incomplete proteins, except for soy.
Complementary proteins are two incomplete proteins that, when consumed together, provide all essential amino acids.
Examples of complementary protein pairings include rice and beans, wheat and peanut butter, pasta and peas, and lentils and almonds.

Leucine and Muscle Protein Synthesis

Leucine is a primary factor for increasing muscle protein synthesis, which facilitates muscle recovery and growth.
The optimal dose of leucine to maximise protein synthesis is 0.05 grams per kilogram of bodyweight.

Protein Timing

Strategic timing of protein ingestion throughout the day, as well as before, during, and after training, can improve long-term physiological adaptations to exercise.

Protein Intake for Muscle Growth

Protein intake frequency is better for muscle growth than timing or amount in a single serving.
Consuming 20 grams of protein every three hours is more effective than 40 grams every 6 hours.
The “anabolic threshold” is the minimum amount of protein needed to stimulate muscle protein synthesis.
The anabolic threshold varies between individuals but is typically around 20 grams for a single serving.
If a meal falls below the anabolic threshold, it may be difficult to stimulate muscle growth, even with high total protein intake.

Optimal Protein Timing for Muscle Growth

Consuming protein every three hours throughout the day maximizes muscle protein synthesis.
A study on overweight or obese individuals found that consuming protein evenly throughout the day with six meals led to greater fat loss and muscle mass maintenance compared to three meals per day.

Post-Workout Protein Consumption

Post-workout protein consumption is less critical to muscle growth compared to total daily protein intake.
However, consuming protein after resistance training might enhance muscle growth.
Post-workout protein may benefit individuals who are already well-trained or are involved in very intensive training programs.

Protein Myths and Hot Topics

There are various myths about protein intake, such as negative impacts on kidney function or superiority of animal protein over plant protein.
While scientific evidence does not support some myths, there is still a need for further research to clarify certain aspects of optimal protein intake.
The scientific evidence does suggest that the anabolic threshold is relevant for achieving optimal muscle growth through protein intake.
Even if a post-workout protein consumption does not display statistically significant muscle growth in studies; the practice can still have a practical benefit.

Protein Fundamentals

Proteins are composed of amino acids, which are obtained from food during digestion.
The body uses these amino acids to form its own proteins.
Some amino acids are essential and must be obtained from the diet.
Leucine plays an important role in signaling muscle protein synthesis.