Chapter 5 Power Point

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Chapter 5 Lecture

Chapter 5:Proteins: Crucial Components of All Body Tissues

Learning Outcomes

1. Describe how proteins differ from carbohydrates and fats.

2. Describe the processes by which DNA directs protein synthesis and proteins organize into levels of structure.

3. Explain the significance of mutual supplementation and identify non-meat food combinations that are complete protein sources.

4. Identify at least four functions of proteins in our body.


Learning Outcomes

5. Explain how our body digests and absorbs protein.

6. Calculate your recommended dietary allowance for protein.

7. Describe two disorders related to inadequate protein intake.

8. Identify several healthful food sources of animal and plant protein.

9. List the types, benefits, and potential challenges of vegetarian diets.


What Are Proteins?

• Proteins: large, complex molecules composed of amino acids

• Contain carbon, hydrogen, oxygen, nitrogen• Primary source of nitrogen in our diets• 20 different amino acids are used to make

proteins.


Amino Acids


Amino Acids

• The structure of an amino acid begins with a central carbon atom.

• The central carbon is surrounded by:• a hydrogen atom• an acid group• an amine group• a side chain that is unique to each amino acid


Structure of Proteins


Structure of Amino Acids


Amino Acids

• Essential amino acids: cannot be produced by our bodies• Must be obtained from food

• Nonessential amino acids: can be made by our bodies


How Are Proteins Made?

• Proteins are long chains of amino acids.• Amino acids are joined to each other by peptide

bonds.• The structure of each protein is dictated by the

DNA of a gene.




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• The three-dimensional shape of a protein:• is determined by the amino acids in the

protein• is critical to the proper function of the protein• can be damaged by heat, acids, heavy

metals, alcohol, and other substances (denaturation)

• shape determines function




Proteins in the Diet

• Incomplete protein: does not contain all essential amino acids• Not sufficient for growth and health• Considered a "low-quality" protein

• Complete protein: contains sufficient amounts of all nine essential amino acids• Considered a "high-quality" protein• Animal protein and soy protein



• Mutual supplementation: using two incomplete proteins together to make a complete protein

• Complementary proteins: two protein sources that together supply all nine essential amino acids• Example: beans and rice




Why Do We Need Proteins?

Proteins:• Contribute to cell growth, repair, and

maintenance• Act as enzymes and hormones• Help maintain fluid and electrolyte balance

• Attract fluids• Fluid in the tissues is called edema.


Why Do We Need Proteins?

Proteins:• Transport nutrients and other substances• Help maintain pH balance• Help maintain the immune system

• Antibodies• Serve as an energy source


Digestion of Proteins


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• Digestion of proteins begins in the stomach.• Hydrochloric acid breaks down protein

structure.• Hydrochloric acid activates pepsin.

• Pepsin: an enzyme that breaks down proteins into short polypeptides and amino acids



• Digestion of proteins continues in the small intestines.• Pancreatic enzymes called proteases

complete the digestion of proteins to single amino acids.

• Waste product of protein breakdown is urea (amine group).

• Indigestible proteins are of lower quality for nutrition.


Absorption of Proteins


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How Much Protein Should We Eat?

• Proper protein intake depends on:• activity level• age• health status

• Example: Each day, a sedentary adult requires 0.8 g of protein per kg of body weight.



• People who require more protein include:• children• adolescents• pregnant or lactating women• athletes




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• Recommended Dietary Allowance (RDA)• 0.8 g protein per kg body weight• 12–20% of total energy intake should be from

protein




Protein-Energy Malnutrition

• Marasmus• A systemic disease characterized by grossly

inadequate energy, especially protein sources


Protein-Energy Malnutrition

• Kwashiorkor• Systemic disease characterized by

malnutrition and inadequate protein sources


Can Too Much Dietary Protein Be Harmful?

The risks of too much protein may include:• Cardiovascular disease

• Diets high in protein from animal sources MAY increase the risk of cardiovascular disease.

• Bone loss• High-protein diets MAY cause excess calcium

excretion leading to bone loss.


Can Too Much Dietary Protein Be Harmful?

• The risks of too much protein may also include kidney disease.• High-protein diets can be difficult for people

with kidney problems.• There is no evidence that high-protein diets

cause kidney disease in healthy people.


Sources of Protein

• Good sources of protein include:• meats• dairy products• soy products• legumes• whole grains• nuts


Sources of Protein


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Protein Content of Selected Foods


Vegetarian Diets

• Vegetarianism: restricting the diet to foods of vegetable origin (including fruits, grains, nuts)

• There are many versions of vegetarianism.• There are many reasons to adopt a vegetarian

diet.


Vegetarian Diets


Why Vegetarianism?

• People choose vegetarianism for:• Health benefits• Ecological reasons• Religious reasons• Ethical reasons• Food safety concerns


Health Benefits of Vegetarianism

• Fewer intestinal problems• Reduced risk of:

• Obesity, type 2 diabetes• Heart disease and high blood pressure• Some types of cancer• Kidney disease, kidney stones, gallstones


Challenges of Vegetarianism

• Vegetarian diets can be low in some vitamins and minerals.

• Vegetarians must carefully plan a balanced and adequate diet.

• Vegetarians can use soy products as a protein source.





• Vegetarians should include complementary proteins.

• Vegetarians should consult MyPlate for healthy eating tips.

• Vegans need to supplement with Vitamin B12.
