Study Notes on Human Energy and Metabolism

Human Energy & Metabolism

Chapter Overview

  • The study looks into human metabolism with a focus on energy production and storage.

Caloric Measurement

  • Calorie Definition:

    • The most common measure of energy.

    • Defined as the amount of heat needed to raise 1 kg of water by 1 degree Celsius.

Energy Content of Macronutrients

  • Energy Values: In Calories (C)

    • Carbohydrate: 4 C per gram.

    • Fat: 9 C per gram.

    • Protein: 4 C per gram.

    • Alcohol: 7 C per gram.

Energy Content Examples

  • Measurement Examples

    • 1 teaspoon of sugar (5 grams carbohydrate) contains 20 Calories.

    • 1 teaspoon of salad oil (5 grams fat) contains 45 Calories.

Mechanisms of Energy Storage in the Body

Carbohydrate Storage

  • **Forms of Carbohydrate Storage: **

    • Blood glucose: Immediate source of energy.

    • Liver glycogen: Storage form for longer-term use.

    • Muscle glycogen: Local storage for energy during exercise.

Fat Storage

  • Forms of Fat Storage:

    • Triglycerides within muscle tissue and adipose (fat) tissue.

    • Triglycerides and free fatty acids are available in the blood, though limited in supply.

Protein Storage

  • Primarily found in muscle tissue, not an efficient energy source.

Overview of Human Metabolism

  • Nutritional Inputs and Energy Production Route:

    • Nutrients: Protein (Amino acids), Carbohydrate (Glucose), Fat (Fatty acids).

    • Resulting in: Acetyl CoA, which enters the Krebs cycle, leading to ATP production via the Electron Transport Chain.

Human Energy Systems

  1. ATP/PCr (Phosphagen System)

    • Involves: Adenosine Triphosphate (ATP) and Phosphocreatine (PCr).

    • Function: Provides “all out” rapid energy for short (5-10 seconds) bursts of intense exercise.

    • Limitation: Supply of ATP can be quickly depleted.

    • Requirement: ATP must be available for muscle contraction.

  2. Lactic Acid System

    • Mechanism: Muscle glycogen is broken down via glycolysis.

    • Differentiation:

      • Aerobic Glycolysis: Requires oxygen; produces a lot of ATP.

      • Anaerobic Glycolysis: Limited oxygen; produces less ATP, lactic acid is a byproduct.

    • Implication: Lactic acid might contribute to fatigue during high-intensity exercise.

  3. Oxygen System

    • Involves carbohydrates, fats, and protein as energy sources, using the Electron Transport Chain and Krebs Cycle.

    • Benefit: Produces ATP in large quantities when oxygen is available.

    • Limitation: Cannot meet high energy demand during maximal exercise.

Types of Energy Production Processes

  • Aerobic Glycolysis:

    • Utilizes carbohydrates for energy production, specifically muscle glycogen and blood glucose.

  • Aerobic Lipolysis:

    • Utilizes fats for energy production, specifically muscle triglycerides and blood free fatty acids (FFA).

Anatomy of Metabolism

General Definition

  • Metabolism: The sum total of all physical and biochemical reactions within the body.

Metabolism at Rest

  • Basal Metabolic Rate (BMR):

    • Represents metabolic rate when at rest.

    • Higher focal points include Resting Metabolic Rate (RMR) and Resting Energy Expenditure (REE).

Estimating Resting Energy Expenditure (REE)

  • Rough Estimate: - 1 Calorie per kg per hour.

  • Factors Affecting REE:

    • Age, gender, activity level, body composition, and genetics.

Influences on REE

  • Decrease in body weight typically lowers REE.

  • Very low-calorie diets can significantly decrease REE through lowered metabolic hormone levels.

  • Maintaining normal weight while reducing body fat and increasing muscle mass can raise REE.

Thermic Effects and Total Energy Expenditure

Thermic Effect of Food (TEF)

  • Maximum TEF observed about one hour after a meal, lasting approximately four hours.

  • Correlation: Higher caloric intake results in a higher TEF.

  • Findings: Lean subjects exhibit significantly higher TEF compared to obese subjects.

Thermic Effect of Exercise (TEE)

  • Efficiency of movement directly influences caloric expenditure.

Total Energy Expenditure (TEE) Components

  • Recognition of REE, TEF, and TEE contributions:

    • REE: 60-75% of total energy expenditure.

    • TEF: 5-10%.

    • TEE: 15-30%, varying from 0% for sedentary individuals to 50% for ultra-endurance athletes.

Factors Influencing Caloric Requirements

  • Involves factors such as height, weight, gender, age, sport, and activity level.

  • Physical Activity Level (PAL) Determined by:

    • Sedentary

    • Low active

    • Active

    • Very active.

Additional Influencing Factors on Energy Availability During Exercise

  • Hormones: Influence metabolism and energy availability.

  • Training Status: Levels of exertion can impact energy usage.

  • Dietary Composition: Affect energy provision.

  • Timing of Meals: Eating before competitions matters.

  • Nutritional Status: Overall nutrition can influence energy availability.

  • Nutrient Intake During Exercise: Nutrients consumed during exercise can assist in energy provision.