Comprehensive Study Notes: Proteins, Energy Balance, and Vitamins in Nutrition

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Chapter 6: Proteins in Nutrition

Amino Acids and Protein Structure

Proteins are essential macromolecules composed of amino acids, which serve as the building blocks for all proteins in the body. The structure and function of proteins are determined by the sequence and properties of their constituent amino acids.

Amino Acid Structure: Each amino acid contains a backbone (amino group, carboxyl group, C group) and a unique side chain (R group).
Side Chains: Side chains confer different structural and chemical properties, influencing protein function. They can be:
- Polar: Interact with water, water-soluble
- Nonpolar: Interact with other nonpolar molecules (e.g., fats)
- Positive/Negative: Basic or acidic
Branched Chain Amino Acids (BCAAs): Have side chains with a branched structure. Examples include leucine, isoleucine, and valine. BCAAs are important for muscle health and energy.
Essential vs. Non-Essential Amino Acids: Essential amino acids must be obtained from the diet, while non-essential amino acids can be synthesized by the body.

Peptide Bonds: Amino acids are linked by peptide bonds to form proteins. Proteins contain carbon, hydrogen, oxygen, and nitrogen.

Protein Functions

Proteins perform a wide range of functions in the body:

Transport: Proteins bind to compounds and transport them through body fluids and across cell membranes.
Enzymes: Proteins act as catalysts, speeding up chemical reactions. Example: Enzymes facilitate the breakdown or synthesis of compounds.
Fluid Balance: Proteins help maintain fluid balance by attracting fluid and keeping it in the vessels. They prevent edema by regulating pressure in capillaries.
Acid-Base Balance: Proteins act as buffers, helping to maintain pH balance in the body. They can accept or donate hydrogen ions as needed.
Antibodies: Proteins that fight infections and support immune function.
Hormones: Some hormones are proteins that regulate physiological processes (e.g., insulin, growth hormone).
Energy: Proteins can be used for energy when carbohydrate and fat intake is low, but this is not their primary function.

Protein Metabolism and Requirements

Edema: Swelling caused by fluid accumulation, often due to decreased protein in the blood.
Atrophy: Loss of muscle mass due to decreased protein synthesis or increased breakdown.
Hypertrophy: Increase in muscle mass when protein synthesis exceeds breakdown.
Recommended Protein Intake:
- General:
- Athletes: 1.2–1.4 g/kg/day (endurance); 1.6–2.0 g/kg/day (strength/power)

Protein Sources and Quality

Animal Protein: Chicken, beef, steak, ground turkey, bison
Vegan Protein: Edamame, tofu, beans, tempeh
Fish Protein: Salmon, trout, tuna
Convenient Protein: Protein bars, protein drinks, Greek yogurt, halo top
Complete Proteins: Contain all nine essential amino acids (e.g., animal protein, soy, quinoa)
Incomplete Proteins: Lack one or more essential amino acids (e.g., most plant proteins)

Protein Digestion and Absorption

Mouth: Chewing initiates breakdown.
Stomach: Hydrochloric acid and pepsin denature and hydrolyze proteins.
Small Intestine: Pancreatic enzymes (trypsin, chymotrypsin) further break down proteins into amino acids and small peptides.
Absorption: Amino acids are absorbed into the bloodstream via active transport and carrier proteins.

Protein Synthesis and Metabolism

mRNA: Messenger RNA is transcribed from DNA and translated into amino acid sequences (proteins).
Deamination: Removal of the amino group from amino acids for energy production or conversion to other compounds.
Gluconeogenesis: Formation of glucose from non-carbohydrate sources, including amino acids.

Protein Powders and Supplements

Whey Protein: Rapidly absorbed, supports muscle growth and weight management.
Soy Protein: Plant-based, complete protein, suitable for vegans but may cause digestive issues.
Casein Protein: Slow-release, supports muscle maintenance overnight.
Egg Protein: High-quality, fast-absorbing, rich in essential amino acids.
Pea Protein: Nearly complete, easily digestible, hypoallergenic, often combined with other plant proteins.

Chapter 7: Energy Balance and Body Weight

Energy Balance Concepts

Energy balance is the relationship between energy intake (food) and energy expenditure (body functions and activity). Maintaining energy balance is crucial for body weight regulation.

Catabolism: Breakdown of large molecules into smaller ones, releasing energy.
Anabolism: Assembly of small molecules into larger ones, using energy.
Energy Equilibrium: Intake equals output; weight is maintained.
Positive Energy Balance: Intake exceeds output; weight gain.
Negative Energy Balance: Intake less than output; weight loss.

Total Daily Energy Expenditure (TDEE)

TDEE is the total number of calories burned per day, influenced by several factors:

Basal Metabolic Rate (BMR): Calories burned at rest for basic functions (breathing, heartbeat, temperature). Accounts for 50–75% of daily energy needs.
Physical Activity: Calories burned during exercise (exercise activity thermogenesis, EAT).
Non-Exercise Activity Thermogenesis (NEAT): Calories burned during non-exercise activities (walking, fidgeting).
Thermic Effect of Food (TEF): Calories used to digest and process food (about 10% of total daily energy expenditure).

Factors Affecting Energy Expenditure

Body composition (muscle mass increases BMR)
Age, sex, genetics, hormones, stress
Temperature, illness

Hunger, Appetite, and Satiety

Hunger: Physiological need for food, triggered by low blood sugar and signals from the hypothalamus.
Appetite: Desire for food, influenced by external cues (sight, smell, taste).
Satiety: Feeling of fullness after eating.

Appetite Signaling Hormones

Hormone	Source	Effect	Timing
Ghrelin	Stomach	Increases hunger	Before meals
Leptin	Fat cells	Signals fullness	Long-term
Insulin	Pancreas	Promotes storage	After meals
CCK	Intestine	Reduces appetite	Post-meal
GLP-1	Gut	Slows emptying, increases satiety	Post-meal
NPY	Brain	Increases appetite	Before meal

Body Composition and Fat Cells

Fat Cells (Adipocytes): Store energy as triglycerides (TG). Release energy when needed.
Lipogenesis: Formation of fat stores from excess calories.
Lipolysis: Breakdown of fat stores for energy.
Fat Cell Hypertrophy: Increase in fat cell size (first response to excess calories).
Fat Cell Hyperplasia: Increase in fat cell number (with long-term weight gain).
Weight Loss: Fat cells shrink but do not decrease in number.

Obesity and Body Fat Distribution

Gynoid Obesity: Fat stored in hips and thighs (pear-shaped).
Android Obesity: Fat stored around the abdomen (apple-shaped).
Body Fat Percentage: Females: minimum 16%, 25%+ considered obese; Males: minimum 6%, 25%+ considered obese.

Measuring Body Composition

BMI: Body Mass Index, calculated as
Skinfolds: Measures subcutaneous fat thickness.
Bod Pod/Air Displacement: Measures body volume and density.
Underwater Weighing: Gold standard, measures body density via water displacement.

Chapters 9 & 10: Vitamins in Nutrition

Overview of Vitamins

Vitamins are organic compounds required in small amounts for metabolism, growth, and repair. They act as coenzymes, antioxidants, and regulators but do not supply calories.

Deficiency: Leads to symptoms such as fatigue, poor immunity, and abnormal growth.

Major Vitamins and Their Functions

Vitamin	Role	Function
A	Protect, Build	Vision, immune defense
D	Build	Bone growth, calcium balance
E	Protect	Antioxidant for cell membranes
K	Build	Clotting & bone metabolism
C	Protect, Build	Collagen, antioxidant, iron absorption
B1-B3, B6	Energize	Convert macronutrients to ATP
Folate, B12	Build	DNA & red blood cell formation

History and Classification of Vitamins

Discovery: Certain foods prevent diseases (e.g., citrus prevents scurvy, brown rice prevents beriberi).
1940s: Vitamins added to foods to prevent deficiencies.
Fortified Foods: Nutrients added that weren't there originally (e.g., vitamin D in milk).
Enriched Foods: Nutrients lost in processing are replaced (e.g., B-vitamins in white bread).
Classification:
- Fat-soluble: A, D, E, K (absorbed with dietary fat, stored in liver/body fat, risk of toxicity if taken in excess)
- Water-soluble: B-vitamins, C (absorbed & circulated, extra amounts excreted in urine)

Bioavailability and Absorption

Bioavailability: The degree to which a nutrient is absorbed and utilized.
Factors affecting absorption: Food matrix, presence of other nutrients, health status.

Summary and Study Tips

Proteins, energy balance, and vitamins are foundational topics in nutrition.
Understand the structure, function, and sources of proteins and vitamins.
Know how energy balance is regulated and measured.
Be able to classify vitamins and understand their roles in health and disease prevention.