UNIT 3 Energy Metabolism PDF

INTRODUCTION TO HUMAN NUTRITION UNIT 03: Energy Metabolism Dr. Mahpara Safdar Introduction Energy Intake and Expenditure Factors that Influence Energy Expenditure Energy Requirements OUTLINE Energy Balance in Various Conditions Obesity  Energ...

INTRODUCTION TO HUMAN NUTRITION UNIT 03: Energy Metabolism Dr. Mahpara Safdar Introduction Energy Intake and Expenditure Factors that Influence Energy Expenditure Energy Requirements OUTLINE Energy Balance in Various Conditions Obesity  Energy Balance Definition: The relationship between energy intake (from food) Key messages and energy expenditure (for physiological functions and activities). Positive Balance: Energy intake exceeds expenditure → weight gain. Negative Balance: Energy expenditure exceeds intake → weight loss (e.g., starvation). Macronutrient Energy Content Carbohydrates: 16.8 kJ/g Protein: 16.8 kJ/g Fat: 37.8 kJ/g Alcohol: 29.4 kJ/g Total Energy Expenditure (TEE) Resting/Basal Metabolic Rate (BMR): Energy needed for basic functions (heart rate, muscle activity, respiration). Thermic Effect of Food (TEF): ~10% of calorie intake; energy required for digestion and metabolism. Physical Activity: Energy used for skeletal muscle activity; includes exercise and non-exercise activity (e.g., walking, daily tasks). In Infants/Children: Growth energy requirements added.  Energy Requirements Needed to maintain: Body size and composition Activity level Key messages Optimal health Additional needs in: Children: For growth Pregnancy/Lactation: For tissue deposition and milk secretion Body Mass Index (BMI) Categories Normal Weight: 18–24.9 kg/m² Overweight: 25–29.9 kg/m² Obese: ≥30 kg/m² Measuring Energy Expenditure Direct Calorimetry: Measures heat output. Indirect Calorimetry: Measures oxygen consumption and CO2 production. Doubly Labeled Water: Modern gold standard; non- invasive measurement of total energy expenditure over 7–14 days in free-living conditions. Hunger vs. Appetite Hunger: Physiological need for food. Appetite: Psychological desire for food, often influenced by environmental cues and learned behaviors. 3.1 Introduction  What is Energy Balance? Definition and Definition: The state where the amount of energy conceptualizatio consumed equals the amount of energy expended. Most adults consume approximately 1,000,000 calories (4,000 MJ) per year. n of energy Despite large fluctuations in daily intake and expenditure, most healthy individuals maintain a balance stable energy balance. Energy Balance as an Example of Homeostasis Homeostatic Control: The body’s ability to maintain stable conditions despite daily fluctuations. Function: Energy balance ensures the maintenance of body weight and energy stores. Accuracy of Energy Balance Even minor imbalances can have significant effects over time. Example: An excess of just 105 kJ/day (25 calories) can lead to significant weight gain over time. Small, consistent imbalances can cause obesity or weight loss.  Definition and conceptualization of energy balance Role of Thermodynamics in Energy Balance First Law of Thermodynamics: Energy can neither be created nor destroyed, only converted. Energy intake equals energy expenditure = constant body energy stores. “Energy in → → Energy out → No change in body energy stores.” Definition and Mechanisms of Energy Balance conceptualization of Energy Intake: Driven by food energy balance consumption (carbohydrates, proteins, fats, alcohol). Energy Expenditure: Includes basal metabolic rate (BMR), thermic effect of food (TEF), and physical activity. The body adjusts between meals or activity to maintain balance in the long term. Methods to Measure Body Energy Stores 1. Direct Methods: Calorimetry (measuring heat production). 2. Indirect Methods: Oxygen consumption, CO2 production.  Definition and conceptualizatio n of energy balance Disruptions in Energy Balance Positive Energy Balance: Excess energy intake leading to weight gain. Negative Energy Balance: Excess energy expenditure leading to weight loss. Obesity as an Outcome of Positive Energy Balance The result of chronic energy intake exceeding expenditure. Global Health Issue: Obesity is now considered one of the major nutritional disorders. “Obesity = Chronic positive energy balance.” Factors Leading to Disruptions Unbalanced diets, sedentary lifestyle, metabolic disorders Components of Energy Balance Understanding Energy Intake, Storage, 2. Energy Storage and Expenditure Forms of Energy Storage: Energy balance occurs when the energy intake from food Fat: Major energy reserve equals the energy expended by the body. Glycogen: Short-term energy reserve Maintains body weight and energy stores. Disruption leads to weight gain or loss. (stored in liver and muscles) Components: Protein: Used in extreme cases like 1. Energy intake starvation 2. Energy storage Storage Process: Excess energy from food 3. Energy expenditure is stored in the body, primarily as fat. 1. Energy Intake Definition: Energy intake refers to the caloric content of food. Sources: Carbohydrates: 16.8 kJ/g Proteins: 16.8 kJ/g Fats: 37.8 kJ/g Alcohol: 29.4 kJ/g Role: Provides the body with energy to fuel daily activities and bodily functions. Components of Energy Balance 3. Energy Expenditure The total energy used by the body is split into three main components: 1. Basal Metabolic Rate (BMR) Definition: Minimum energy required to maintain basic physiological functions (heartbeat, breathing, muscle function). Measurement: Done after a 12-hour fast, in a resting state. RMR: Resting Metabolic Rate is slightly higher (~3%) due to less controlled conditions. RMR in adults: ~4.2 kJ/min, comprising two-thirds of total energy expenditure. Components of Energy Balance 3. Energy Expenditure 2. Thermic Effect of Food (TEF) Definition: The increase in metabolic rate after eating. Energy is used to digest, absorb, and store macronutrients. TEF Proportion: Typically 10% of the caloric content of a meal. Obligatory Thermogenesis: Energy for digestion. Facultative Thermogenesis: Additional energy from sympathetic nervous system activation. Components of Energy Balance Other Components of Energy 3. Physical Activity Energy Expenditure Expenditure Growth: Mainly in infants and children. Definition: Energy used by skeletal Adaptive Thermogenesis: Heat production muscles for movement. in response to cold, fever, or other Includes: Exercise and non-exercise conditions. activities. Thermogenic Agents: Substances like Variability: Highly variable between nicotine, caffeine, and capsaicin that individuals based on physical activity increase energy expenditure. level. Energy Balance Definition: Energy balance occurs when energy intake equals energy expenditure. Positive Energy Balance: Excess energy is stored as fat. Negative Energy Balance: Energy deficiency leads to depletion of fat stores. Examples: Positive during pregnancy, negative during starvation. Adaptive Thermogenesis Definition: Changes in energy expenditure beyond body weight changes. Occurs: During significant energy imbalances like obesity treatment or overfeeding. Effect: May cause resistance to fat loss or create new weight plateaus. Macronutrient Balance Carbohydrate Balance: Occurs when the amount of carbohydrates consumed equals that expended for energy. Protein and Fat Balance: Similar mechanisms for maintaining equilibrium. 3.2 Energy Intake 3.2 Energy Intake Macronutrient Contribution to Total Energy Carbohydrate Contribution: 21 g = 352.8 kJ → 352.8/820×100=43% Fat Contribution: 6 g = 226.8 kJ → 226.8/820×100=28% Protein Contribution: 14 g = 235.2 kJ → 235.2/820×100=29% Key Points Energy intake is derived from macronutrients: carbohydrates, proteins, fats, and alcohol. Energy content can be accurately measured using bomb calorimetry. Understanding the macronutrient composition is vital for assessing dietary energy. Importance of Energy Intake Maintaining Energy Balance: Crucial for overall health and weight management. Impact of Imbalanced Energy Intake: Positive energy balance can lead to weight gain. Negative energy balance can result in weight loss. Energy intake is a fundamental aspect of nutrition. Awareness of sources and energy content helps make informed dietary choices. 3.2 Energy Intake Regulation of Food Intake Appetite, Hunger, and Satiety Food intake is regulated by complex interactions involving: Hormones Neuroendocrine factors Central Nervous System (CNS) Organ systems (e.g., brain and liver) Environmental and external factors Appetite: Psychological desire to eat. Related to pleasant sensations associated with food. Hunger: Subjective feeling prompting food consumption. Nagging sensation indicating food deprivation. Satiety: State of inhibition over eating. Leads to meal termination and indicates the time until the next meal. Intrinsic and Extrinsic Factors Intrinsic Factors: Central Nervous System: Hypothalamus and vagus nerve. Digestive organs: Stomach and liver. Hormones: Regulate hunger and satiety. Extrinsic Factors: Environmental: Meal patterns, food availability, sensory cues (smell, sight). Emotional: Stress and its impact on food intake. 3.2 Disease states: Anorexia, trauma, infection. Influencing Appetite Energy External Factors: Climate and weather. Specific cravings and learned dislikes (e.g., Intake alcohol). Food Properties: Taste, palatability, and texture. Cultural Practices: Cultural norms and preferences affecting food choices.  3.2 Energy Intake Other Influences: Effects of certain drugs and diseases. Metabolic factors (hormones, neurotransmitters). The Satiety Cascade A framework proposed by John Blundell to describe mechanisms regulating satiety. Categories: Mechanisms involved in acute within-meal satiety (satiation). Mechanisms influencing between-meal satiety. Key Notes: Understanding the regulation of food intake involves multiple interacting factors. Both intrinsic and extrinsic factors play significant roles in appetite, hunger, and satiety. Knowledge of these factors can inform strategies for managing food intake and combating obesity.  Intrinsic vs. Internal Factors Energy Intake and Influencing Factors Influencing Food Intake: Learned Responses: Regulating Food Intake Factors Hunger and satiety Hormonal Central Nervous interactions are intrinsic; System: Neuroendocrine appetite is often Stomach, liver factors learned. Hormonal Influences: Central nervous CCK, GLP-1, GIP system involvement External environmental factors  Energy Intake and Influencing Factors 1. Digestive Factors Gastrointestinal Distension: Pressure from food/drink in stomach and intestine regulates intake. Macronutrient Receptors: Receptors in the intestine link to the brain to regulate energy balance. Hormonal Influences: Gastrointestinal hormones : Cholecystokinin (CCK) is produced in response to food intake. glucagon-like peptide-1 and -2 (GLP-1), insulinotropic polypeptide (GIP) play a role in the mediation of gut events and brain perception of hunger and satiety  2. Central Nervous System Factors 3. Circulating Factors Energy Intake and Influencing Hypothalamus Role: Links to paraventricular nuclei and Post-Meal Metabolism: Breakdown of food into glucose, Factors nigrostriatal tract (known to modify feeding behavior). amino acids, glycerol, and fatty acids. Sympathetic Nervous System: Increase in circulating levels post- Increased activity decreases food meal. intake. Nutrient Metabolism Regulation: Signals from the liver via the vagus nerve influence food intake. Energy Intake and Influencing Factors Signals from the Periphery Leptin: Hormone from fat cells influencing the hypothalamus. Adiposity Signals: Insulin, leptin, adiponectin - long-acting signals reducing energy intake. Satiety Signals: Ghrelin (hunger hormone), CCK, PYY, GLP- 1, OXM, PP - short-term regulators. Role of the Arcuate Nucleus (ARC) ARC Functions: Contains neurons regulating food intake. NPY and AgRP: Stimulate food intake. POMC and CART: Inhibit feeding. Additional Structures: Nucleus of the solitary tract (NTS) and area postrema (AP) connections to hypothalamic nuclei. Energy Intake and Influencing Factors External Factors Influencing Food Intake Non-Physiological Influences: Psychological factors (e.g., depression) affecting consumption. Environmental factors (e.g., food availability). Food Properties: Taste, texture, color, temperature, presentation. Cultural Influences: Time of day, social factors, peer influence, cultural preferences. Key Points: Energy intake is influenced by a complex interplay of internal and external factors. Understanding these factors is essential for promoting healthy eating behaviors. 3.3 Energy Expenditu re 3.3 Understanding the Energy Concept and Its Expenditu Importance Definition of Energy Expenditure re The process by which the body uses energy derived from food. Analogous to a wood stove burning wood to release heat. Energy Oxidation Process Oxidation of Food Food is oxidized in the presence of oxygen. Releases carbon dioxide, water, and heat. Example Reaction: Glucose Combustion C6H12O6+6O2→6H2O+6CO2+Heat Importance of Gradual Energy Release Controlled Energy Release Energy is released gradually through metabolic pathways. Ensures a steady energy supply rather than sudden bursts. 3.3 Understanding the Energy Concept and Its Expenditu Importance Major Sources of Energy Expenditure re Three Major Components: 1. Resting Metabolic Rate (RMR) Energy used at rest to maintain vital functions. 2. Thermic Effect of Meals (TEM) Energy used in digestion and absorption of food. 3. Thermic Effect of Exercise (Physical Activity) Energy expended during movement and exercise. Measuring Energy Expenditure Methods of Measurement Direct Calorimetry: Measures total heat production in the body. Indirect Calorimetry: Assesses oxygen consumption and carbon dioxide production. Key Points Energy expenditure is crucial for maintaining bodily functions. Understanding the processes involved can help in nutritional planning and weight management.  Methodology of Energy Expenditure and Its Antoine Lavoisier: Lavoisier’s Experiments Lavoisier’s Calorimeter Significance of Lavoisier’s Work Historical Aspects Worked in the late eighteenth century in France. Key Discoveries: Found that a candle burns only in the presence of Setup: Small animal placed in a sealed chamber with ice Pioneering Contribution: First to document and Pioneered studies on heat oxygen. around it. quantify heat production in production in living Demonstrated that living Insulated chamber to living organisms. organisms. organisms produce heat by prevent heat loss. Legacy: combusting food. Measurements: Laid the groundwork for First Calorimeter: Collected and measured future research in Designed to measure heat the volume of melting ice. metabolism and energy production in small Calculated heat production expenditure. animals. based on melted ice Understanding energy volume. expenditure is vital for health and metabolism. Historical studies, particularly by Lavoisier, have significantly contributed to this field Direct Calorimetry Definition: Measuring heat Measurement production directly Methods of Technical challenges and infrequent use in human Energy studies Expenditure Indirect Calorimetry Definition: Measuring energy production through respiratory gas analysis Importance of oxygen consumption and carbon dioxide production Measurement Indirect Calorimetry Methods of Techniques Short measurement periods at rest or Energy during exercise Long-term measurements in Expenditure metabolic chambers BMR Measurement Conditions: Fasted state, resting position, early morning Duration: 30-40 minutes Thermic Effect of Meals (TEM) Definition: Energy expended during digestion and absorption Measurement: Monitoring metabolic rate changes for 3-6 hours post-meal Importance of understanding energy contribution from meals Measurement Methods of Energy Expenditure Physical Activity Energy Expenditure Measuring energy expenditure during standard activities in a lab Free-living assessment methods: Doubly Labeled Water (DLW): Total energy expenditure measurement Combining DLW with indirect calorimetry for resting energy expenditure and TEM Respiratory Quotient (RQ) Definition: Ratio of carbon dioxide production to oxygen consumption Significance in substrate oxidation: Carbohydrate oxidation: RQ = 1.0 Fat oxidation: RQ ≈ 0.7 3.4 Factors That Influence Energy Expenditur e  Definition: RMR is the energy expended by the body at rest to maintain basic physiological functions. Variability: Highly variable between individuals (±25%) Consistent within individuals ( 1.75. Optimal PAL for Obesity Prevention: Suggested PAL around 1.8 or higher. 3.6 Energy Balance in Various Conditions Energy Intake During Infancy Energy Intake Trends: First Month: ~525 kJ/kg per day. Eighth Month: Nadir of ~399 kJ/kg per day. Twelfth Month: Rises to ~441 kJ/kg per day. Total Energy Expenditure (TEE): Relatively constant at ~252–294 kJ/kg per day during the first year. Positive Energy Balance: Essential for growth; significant energy accretion in early months. Energy Accretion During Growth Energy Accretion in the First 3 Months: ~701.4 kJ/day (approx. 32% of intake). Energy Accretion by One Year: Falls to ~151.2 kJ/day (approx. 4% of intake). Factors Affecting Variations: Individual growth rates and feeding behaviors.  Energy Intake During Infancy Reevaluation of Energy Requirements Overestimation of Needs: Traditional recommendations may overestimate true energy needs. Discrepancy in the First Year: Recommendations overestimate energy needs by ~11%. Discrepancy Between Ages 1- 3: Traditional values are ~20% higher than actual measured TEE.  Energy Needs in Children 3-Year-Old Energy Needs: Average TEE measured by DLW: ~5.1 MJ/day. Recommended intake: 6.2 MJ/day. Need for newer estimates based on actual TEE data. TEE Measurements in Young Children Global Measurements: Total energy expenditure data collected from various locations worldwide. Geographical Variability: Environmental factors and sociocultural influences can affect TEE. Energy Needs in 5-Year-Olds Average TEE for a 5-Year-Old (20 kg): Approximately 5.5–5.9 MJ/day. Comparison to Recommendations: Lower than recommended daily allowance by Aging and Energy Balance Increase in Fat Mass Consequences: Increased risk of obesity and related diseases. Impacts mobility and overall health. Factors Influencing Fat Gain: Sedentary lifestyle. Changes in metabolism and hormonal balance. Diminished Self-Regulation of Energy Balance Aging may impair the body's ability to self-regulate energy intake and expenditure. Increased risk of both undernutrition and overnutrition. Individual Energy Requirements in the Elderly Tailoring energy needs can help prevent age- related body composition changes. Strategies: Assessing individual health conditions. Monitoring dietary intake and physical activity.  Aging and Energy Balance Special Hypermetabolic Strategies for Considerations Condition Maintaining for Neurological Misconception Energy Balance Conditions Conditions: Previous Nutritional Alzheimer's and Belief: Interventions: Parkinson's Increased Encourage nutrient- disease. metabolic rate in dense foods to meet energy needs Risk of neurological without excessive Malnutrition: conditions leads intake. to higher energy Consider Associated with needs. supplements if decreased food Current needed to prevent intake. malnutrition. Understanding: Often leads to Physical Activity: Weight loss is unintended primarily due to Promote regular weight loss. physical activity reduced food tailored to intake, often individual abilities linked to loss of to maintain muscle functionality. mass and functionality. Energy Requirements in Physically Active Groups Focus on DLW Technique: Used to assess energy requirements in highly active individuals. Provides accurate measurement of total energy expenditure (TEE). Extreme Case: Tour de France Cyclists Study Overview: Energy requirements during the 3-week race. Recorded a PAL factor of 5.3. Total energy expenditure reached 35.7 MJ/day. Significance: Highest sustained level of energy expenditure recorded in humans. Energy Requirements in Other Active Groups Young Male Soldiers: Training for jungle warfare. Energy requirements of 19.9 MJ/day (PAL factor of 2.6). Mountaineers: Climbing Mount Everest. Total energy expenditure: 13.6 MJ/day (PAL 2.0–2.7). Collegiate Swimmers: Energy expenditure: 16.8 MJ/day (men) and 10.9 MJ/day (women). Energy Requirements in Physically Active Groups Elite Female Runners Previous Studies: Suggested unusually low energy requirements. Recent Findings: Free-living energy expenditure: 11.9 ± 1.3 MJ/day. Reported energy intake: 9.2 ± 1.9 MJ/day. Conclusion: Underreporting of energy intake among elite female runners; no energy-saving metabolic adaptations observed. Regular Exercise and Energy Requirements Traditional Beliefs: Regular exercise increases energy requirements due to direct costs and increased resting metabolic rate (RMR). Elderly Volunteers Study: No significant change in total energy expenditure after 8 weeks of vigorous endurance training. RMR increased from 6703.2 ± 898.8 kJ/day to 7404.6 ± 714 kJ/day. Additional energy from exercise: 630 kJ/day. Energy Requirements in Physically Active Groups Compensatory Energy-Conserving Adaptations Observations: Reduction in physical activity energy expenditure during non-exercising time (from 2.4 ± 1.6 to 1.4 ± 1.9 MJ/day). Explanation: Compensatory adaptations to vigorous training can lead to reduced spontaneous and voluntary physical activity. Implications for Energy Requirement Assumptions Energy requirements are not automatically elevated by participation in activity programs. The net effect on energy requirements depends on the intensity of training and the overall change in energy expenditure components. Energy Requirements in Pregnancy and Lactation Pregnancy and lactation involve significant alterations in energy metabolism. Achieving positive energy balance is crucial during these periods. Energy Requirements During Pregnancy Traditional guidelines recommend an increase of 1.3 MJ/day in energy requirements during pregnancy. This figure is based on theoretical calculations related to energy accumulation. Complexity of Energy Changes Factors Influencing Changes: Specific changes in energy requirements are unclear. Various factors affect energy needs, including: Metabolic efficiency adaptations. Physical activity level (PAL) changes during pregnancy. Energy Requirements in Pregnancy and Lactation Study Findings on Energy Expenditure A study measured 12 women every 6 weeks throughout pregnancy. Average increase in total energy expenditure: 1.1 MJ/day. Average energy cost of pregnancy (total energy expenditure + energy storage change): 1.6 MJ/day. Variation among subjects: Total energy expenditure increase: 264.6 kJ/day to 3.8 MJ/day. Energy cost of pregnancy: 147 kJ/day to 5.2 MJ/day.  Energy Requirements During Lactation Energy Cost of Lactation: Investigated using the DLW technique in well- Energy nourished women. Average energy cost of lactation calculated at Requireme 3.7 MJ/day. Sources of Energy During Lactation nts in Breakdown of Energy Cost: Pregnancy Over half of the energy cost achieved through: Increased energy intake. and Remaining energy met by: Decrease in physical activity energy Lactation expenditure. Comparative Data: Energy expenditure at 8 weeks of lactation: 3.2 MJ + 873.6 kJ/day. Pre-pregnancy energy expenditure: 3.9 + 1.1 MJ/day. Energy Requirements in Disease and Trauma Assessing Energy Needs in Critical Conditions Energy requirements can change significantly during disease or trauma. Importance of accurately assessing energy needs for hospitalized patients. Importance of Assessing Energy Requirements Altered Energy Expenditure: Energy expenditure can be modified by disease or injury. Impaired Physical Activity: Physical activity levels are often reduced in hospitalized patients. Risk of Metabolic Complications: Both underfeeding and overfeeding can lead to complications; correct energy assessment is crucial for recovery. Metabolic Response in Burn Recovery Increased Resting Metabolic Rate (RMR): Recovery from burn injuries typically shows an increase in RMR. Not solely dependent on the extent of the burn. Traditional Energy Needs Estimation: Common formulas suggest energy needs of 2–2.5 times RMR.  Findings from DLW Technique in Burn Energy Patients Total energy expenditure in 8-year-old children recovering from burns measured at 6.7 ± 2.9 MJ/day. Requirements in Equivalent to 1.2 times the non-fasting RMR. Implications: Disease and RMR in burn patients is lower than previously thought. Improved wound care likely reduces heat loss, Trauma impacting energy needs. Hospitalization contributes to lower energy requirements due to reduced activity. Energy Requirements in Anorexia Nervosa Total energy expenditure in anorexia nervosa patients was similar to age-, gender-, and height-matched controls. Physical Activity: Activity-related energy expenditure was 1.3 MJ/day higher. RMR was 1.3 MJ/day lower in patients. Despite component alterations, overall energy requirements in anorexia nervosa are normal. Energy Expenditure in Cystic Fibrosis Infants with Cystic Fibrosis: Total energy expenditure elevated by 25% compared to weight-matched controls. Underlying mechanisms for increased energy expenditure remain unknown.  Energy Requirements in Disease and Trauma Energy Balance in Developmental Disabilities Cerebral Palsy: Associated with reduced fat mass and FFM. Myelodysplasia: Approximately half of patients are obese. Unknown Factors: Relationship between body composition and energy expenditure/food intake is unclear. Early life alterations in energy expenditure may influence obesity. Total Energy Expenditure in Adolescents Lower total energy expenditure in adolescents with cerebral palsy and myelodysplasia. Reduction in energy expenditure attributed to decreased RMR and physical activity. Energy Requirements: Nonambulatory: Estimated to be 1.2 times RMR. Ambulatory: Ranges from 1.6–2.1 times RMR. 3.7 Obesity 3.7 Obesity Basic Metabolic Principles Definition: Obesity is the most common form of disruption in energy balance. Considered a major and prevalent nutritional disorder. Health Implications: Strongly associated with various health risks. Recognized as a disease by health professionals. Energy Storage Hierarchy Energy Sources: Continuous consumption of carbohydrates, proteins, fats, and alcohol. Fat is the primary energy store in the body. Mechanisms of Energy Utilization Alcohol: No storage capacity; immediately oxidized for energy. Protein: Limited storage capacity with highly regulated metabolism. Carbohydrates: Stored as glycogen in the liver and muscles. Short-term energy store, quickly depleted.  3.7 Obesity Carbohydrate Metabolism Adaptation to Excess Carbohydrates: Body increases carbohydrate utilization as fuel. Excess carbohydrates may lead to de novo lipogenesis, but typically a minor process. Fat Metabolism Absence of Adaptive Mechanism: No mechanism for increased fat utilization when excess fat is consumed. Storage Efficiency: Excess fat is stored with a low metabolic cost, making fat storage very efficient. Storage Efficiency Comparison Glycogen Storage: Requires hydration: 3 grams of water per gram of glycogen. 4 grams of storage tissue yields only 16.8 kJ (4.2 kJ/g). Fat Storage: Fat does not require water for storage. More efficient: 37.8 kJ/g of stored fat. Energy Storage Calculations Fat Energy Storage: 15 kg of fat = 567.0 MJ of stored energy. 8.4 MJ/day required for survival = sufficient for nearly 70 days without food. 2. Glycogen Storage Requirement: Storing equivalent energy in glycogen would require 135 kg due to hydration.  Overview of Obesity Definition of Obesity Excess accumulation of body energy, primarily as fat A disease of positive energy balance Results from dysregulation in energy balance systems Health Risks and Body Fat Distribution Health Risks of Obesity Increased health risks linked to body fat distribution Variability in health risks among individuals Key Factors in Defining Obesity Indices of body fat accumulation Patterns of body fat distribution Alterations in health risk profile Body Mass Index (BMI) Definition and Calculation Formula: BMI=Weight (kg)/Height (m)2 Units: kg/m² Classification of BMI Obesity in Adults: BMI > 30.0 kg/m² Normal Range: 18.5 – 24.9 kg/m² Overweight: 25 – 30 kg/m² Children: Use age-adjusted BMI percentile  Limitations of BMI Does not differentiate between muscle and fat weight Variability in body fat levels at the same BMI Example of Misclassification Heavy athletes (e.g., football players, bodybuilders) with high muscle mass may have high BMI but are not obese. Overvie Anthropometric Indices of Body Shape Importance of Body Fat Distribution Health risks closely linked to distribution of body fat w of Excess abdominal fat is particularly concerning Useful Indices Waist-to-hip ratio: Marker of body fat distribution Obesity Waist Circumference Waist Circumference as an Index Recommended measurement: midpoint between lowest rib and iliac crest Risk Thresholds Increased risk of obesity-related diseases: Men: Waist circumference > 94 cm Women: Waist circumference > 80 cm  Etiology of Obesity: Excess Intake or Decreased Physical Activity Obesity is a condition resulting from a positive energy balance. Defined as increased energy intake relative to energy expenditure. Often viewed as a result of overeating or lack of physical activity. The etiology of obesity is more complex and multifactorial. Complex Factors Contributing to Obesity Obesity arises from a combination of: Cultural Factors: Societal norms and food availability. Behavioral Factors: Lifestyle choices and eating habits. Biological Factors: Genetics and metabolic processes. Interrelated Factors No single cause; multiple factors interact to influence obesity. Individual Susceptibility Genetic predisposition, hormonal influences, and cultural context contribute to individual risks. Etiology of Obesity: Excess Intake or Decreased Physical Activity Obesity can develop slowly, with energy imbalances being subtle and often undetectable. Genetic and Environmental Factors Genetic Influences Genetics significantly impact body-weight regulation. However, the rapid increase in obesity prevalence is unlikely due to changes in the gene pool. Environmental Changes Acute shifts in behavior and environment are key contributors to obesity growth. Behavioral Changes Leading to Obesity Dietary Changes Increased consumption of high-fat, energy-dense fast foods. Larger portion sizes contributing to higher caloric intake. Sedentary Lifestyle Increased reliance on technology and convenience leading to decreased physical activity. Etiology of Obesity: Excess Intake or Decreased Physical Activity Examples of Sedentary Lifestyle Factors Decreased Physical Activity Automated transport usage instead of walking or cycling. Central heating and automated household appliances reducing physical activity. Workplace Sedentariness Computerization and automation reduce physical demands in the workplace. Lifestyle Influences on Obesity Leisure Activities Increased screen time from televisions and computers. Preference for elevators and escalators over stairs. Environmental Concerns Fear of crime limiting outdoor activities. Urban planning issues that lack adequate walking and cycling infrastructure.  The Principle of Energy Balance Understanding Energy Balance Weight maintenance occurs when energy intake equals energy expenditure. Discrepancies arise from either high food intake or low energy expenditure. Role of Physical Activity Physical activity is the main modifiable factor in energy expenditure. Targets for Obesity Prevention Behavioral Modifications Dietary patterns and physical activity levels are targets for obesity prevention programs. Early Life Interventions Childhood patterns of diet and activity significantly influence future obesity risk. Role of Common belief: Reduced energy expenditure leads to obesity. Physical Controversial nature of this hypothesis. Evidence of Relationships Activity Inverse Relationship: Lean individuals (e.g., athletes) typically show lower obesity rates. and Positive Relationship: Obese individuals often exhibit lower physical activity levels. Energy Mixed Study Outcomes: Some studies link increased TV viewing to obesity risk; others do not. Expenditur Inconsistencies in studies regarding low energy expenditure and obesity. e in the Hypotheses on Physical Activity's Protective Role Developme Physical activity raises overall energy expenditure. May elevate Resting Metabolic Rate (RMR) and reduce nt of positive energy balance risk. Enhanced fat metabolism relative to carbohydrates. Active individuals may maintain energy balance on high- Obesity fat diets.  Role of Physical Activity and Energy Expenditure in the Development of Obesity Limitations of Current Cross-Sectional Studies Research Energy Expenditure Comparison: Cross-Sectional Design Issues: Research shows similar energy expenditure in lean vs. obese individuals when accounting for body composition. Predominance of cross-sectional studies limits the observation of body composition changes over time. Parental Influence: Need for Longitudinal Studies: Mixed results on energy expenditure in children of obese vs. lean parents. Essential to track body fat changes and the impact of energy expenditure during developmental stages. Highlights the necessity of longitudinal studies for clearer insights. Role of Cross-Sectional Studies Physical Energy Expenditure Comparison: Research shows similar energy expenditure in Activity lean vs. obese individuals when accounting for body composition. and Parental Influence: Mixed results on energy expenditure in children of Energy obese vs. lean parents. Highlights the necessity of longitudinal studies for Expenditur clearer insights. Limitations of Current Research e in the Cross-Sectional Design Issues: Predominance of cross-sectional studies limits the Developme observation of body composition changes over time. nt of Need for Longitudinal Studies: Essential to track body fat changes and the Obesity impact of energy expenditure during developmental stages. Intervention Studies Role of Physical Activity and Energy Positive Findings: Expenditure in the Development of Intervention studies often demonstrate that increased physical activity is effective in reducing body fat levels. Obesity Possible Explanations for Discrepant Findings Stage of Maturation: Physical activity's impact may differ at various developmental stages. Longitudinal studies indicate risks associated with reduced energy expenditure in infancy. Individual Differences: Responses to energy expenditure changes may vary among different population subgroups (gender, ethnicity). Some individuals may fail to compensate for energy expenditure fluctuations. References “Introduction to Human Nutrition:, Michael, J Gibney, Hester. H. Vorster and Frans J Kok (2007) Blackwell Sciences https://www.amboss.com/ https://www.ahajournals.org