Chapter 24 Pt 2: Nutrition, Metabolism, and Energy Balance – Study Notes

Nutrition, Metabolism, and Energy Balance

Isocaloric Balance

Isocaloric balance refers to the state where energy intake equals energy expenditure, maintaining body weight. Understanding calories and energy balance is fundamental to nutrition.

• Calorie: A calorie is a unit of energy; specifically, it is the amount of energy required to raise the temperature of 1 gram of water by 1°C. In nutrition, the term "calorie" usually refers to a kilocalorie (kcal).

• Energy Expenditure: Positive energy expenditure means consuming more calories than are burned, leading to weight gain. Negative energy expenditure means burning more calories than consumed, leading to weight loss.

• Fuel = ATP: The body uses nutrients to produce ATP, the energy currency of cells.

Energy-Providing Nutrients

Macronutrients are the nutrients that provide energy for the body. Their caloric values differ.

• Carbohydrates: Provide 4 kcal per gram.

• Proteins: Provide 4 kcal per gram.

• Fats: Provide 9 kcal per gram.

• Alcohol: Provides 7 kcal per gram.

• Essential Nutrients: Nutrients that cannot be synthesized by the body and must be obtained from the diet.

• Calculation Example: To calculate calories eaten: multiply grams of each macronutrient by their respective caloric value and sum the totals.

Example: If a meal contains 10g protein, 20g fat, and 30g carbohydrate: $10 \times 4 + 20 \times 9 + 30 \times 4 = 40 + 180 + 120 = 340$ kcal

Recommended Intakes

Recommended daily intakes vary by macronutrient and are based on health guidelines.

• Carbohydrates: Should make up the majority of daily caloric intake, preferably from complex sources.

• Fats: The "10:10:10:0" guideline refers to the recommended ratio of saturated, monounsaturated, polyunsaturated, and trans fats (trans fats should be avoided).

• Protein: Recommended intake is based on body weight and activity level.

Micronutrients

Micronutrients include vitamins and minerals, which are required in small amounts for proper body function.

• Empty Calories: Foods that provide energy but little or no nutritional value (e.g., soda, candy).

• Fiber-Rich Foods: Nutrition experts recommend these because fiber aids digestion, helps regulate blood sugar, and lowers cholesterol.

Carbohydrates

Carbohydrates are classified by their complexity and function in the body.

• Polysaccharides: Examples include starch and glycogen.

• Storage: Carbohydrates are stored in the liver and muscles as glycogen.

• Main Fuel: The brain and red blood cells prefer carbohydrates as their main fuel source.

• Classification: Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides.

• Importance of Fiber: Fiber is a non-digestible carbohydrate that promotes gut health and regularity.

Fats

Fats are diverse in structure and function, and their types affect health differently.

• Types of Fats:

  • Saturated (e.g., butter)

  • Unsaturated (monounsaturated, e.g., olive oil; polyunsaturated, e.g., fish oil)

  • Trans fats (e.g., processed foods)

  • Essential fatty acids (e.g., omega-3, omega-6)

• Saturation: Refers to the presence of double bonds in fatty acid chains. Saturated fats have no double bonds; unsaturated fats have one or more.

• Importance: Saturation affects melting point and health impact; unsaturated fats are generally healthier.

• HDLs vs LDLs: High-density lipoproteins (HDLs) are "good" cholesterol; low-density lipoproteins (LDLs) are "bad" cholesterol.

Proteins

Proteins are essential for structure and function in the body, and their composition is unique among macronutrients.

• Nitrogen: Proteins contain nitrogen, unlike carbohydrates and fats.

• Amino Acids: There are 20 amino acids; 9 are essential (must be obtained from diet), and 11 are nonessential (can be synthesized).

• Complimentary Protein: Combining foods to provide all essential amino acids (e.g., beans and rice).

• Major Functions: Proteins serve as enzymes, structural components, hormones, and transport molecules.

• Complete Protein: Contains all essential amino acids (e.g., animal proteins).

Table: Major Functions of Proteins in the Body

Function	Example
Enzyme	Amylase, pepsin
Structural	Collagen, keratin
Transport	Hemoglobin
Hormone	Insulin
Defense	Antibodies
Contractile	Actin, myosin
Additional info:	Proteins also regulate pH and fluid balance.

Nitrogen Balance

Nitrogen balance is a measure of protein metabolism and overall health.

• Definition: Nitrogen balance is the difference between nitrogen intake and loss.

• Positive Balance: Intake exceeds loss; occurs during growth, pregnancy, or recovery.

• Negative Balance: Loss exceeds intake; occurs during illness, starvation, or trauma.

• Example: A child in growth has positive nitrogen balance; a patient with muscle wasting has negative balance.

Vitamins

Vitamins are organic compounds required for metabolic processes.

• Number: There are 13 essential vitamins.

• Function: Most act as coenzymes, assisting in biochemical reactions.

• Classification: Water-soluble (e.g., B, C) and fat-soluble (e.g., A, D, E, K).

• Known as: Vitamins are also called micronutrients.

• Intrinsic Factor: Vitamin B12 requires intrinsic factor for absorption.

Minerals

Minerals are inorganic elements essential for various physiological functions.

• Importance: Minerals are needed for bone structure, nerve function, fluid balance, and enzyme activity.

• Examples: Calcium (bone health), iron (hemoglobin), sodium (fluid balance), potassium (nerve function).

Additional info: Minerals must be obtained from the diet, as the body cannot synthesize them.