Human Nutrition Credit 1

Energy Value of Foods

  • The energy value of foods refers to the amount of usable energy that the body can obtain from food.

    • Expressed in kilocalories (kcal).

  • Definition of kilocalorie:

    • One kilocalorie (1 kcal) is defined as the amount of heat energy required to raise the temperature of 1 kilogram of water by 1°C (from 14.5°C to 15.5°C) at normal atmospheric pressure.

  • Conversion to Joules:

    • The International Union of Nutrition Sciences (IUNS) adopted the Joule (J) as the unit of energy instead of kcal.

    • One Joule is defined as the amount of energy required to move one meter by a force of one newton acting on a one-kilogram mass.

Components Providing Energy

  • Key components that supply energy:

    • Carbohydrates, fats, proteins, and alcohol.

  • Energy Release:

    • Energy is released when these compounds are oxidized during respiration.

    • Energy indicates both the amount released from food and the amount expended by the body.

  • Gross Energy Value:

    • The total energy released when food substances are completely oxidized.

    • Not all of this energy is available due to losses in digestion and metabolism.

    • Water, vitamins, and minerals do not provide energy.

Methods of Estimation of Energy Value of Foods

Bomb Calorimeter

  • Direct Calorimetry:

    • Measures the heat produced by a subject or the combustion of a food sample to determine energy expenditure or food energy content.

    • Principle: All energy utilized by the body or released from food eventually converts into heat, measurable directly.

Equipment Used:

  • Bomb Calorimeter: Measures the energy value of food.

  • Atwater and Rosa Respiration Calorimeter: Measures energy expenditure at Basal Metabolic Rate (BMR) or Resting Energy Expenditure (REE).

Bomb Calorimeter Details:

  • Consists of a heavy steel bomb with a platinum lining, sealed in a gold-plated screw collar.

  • A measured quantity of the sample is dried, placed in a bomb, and charged with oxygen to at least 20 atmospheres.

  • The bomb is immersed in a known quantity of water, continuously stirred, with temperature changes recorded at one-minute intervals using a sensitive thermometer.

  • The food sample is ignited electrically, leading to complete combustion; heat released raises the water temperature.

  • Precise thermometer records temperature changes from which energy content is calculated in calories or joules after correcting for radiation and accessory combustion.

Indirect Calorimetry

  • Definition:

    • A method for estimating energy expenditure by measuring respiratory gases involved in metabolism (oxygen consumption VO2 and carbon dioxide production VCO2).

  • Principle:

    • Energy released by the oxidation of food is indirectly proportional to oxygen use and carbon dioxide output.

Equipment Used:

  • Benedict's Oxy Calorimeter: Determines energy value of food.

  • Benedict-Roth Respiration Apparatus: Used to determine BMR.

  • Douglas Bag: Measures energy expenditure during work.

  • Other Devices: Kofrani Michaelis respirometer, Oxylog, Cosmed K₂ respirometer.

Working Details:

  • The subject breathes through a system that collects expired air; volume and concentration of oxygen and carbon dioxide in inspired and expired air are measured.

  • Oxygen consumption is calculated from the difference in oxygen concentration; carbon dioxide production is measured as well.

  • Gas exchange values are combined with metabolic equations (e.g., the Weir equation) to estimate energy expenditure.

  • The respiratory quotient (RQ): ratio of VCO₂ to VO₂, assists in determining which macronutrient is oxidized as each produces a distinct ratio.

Structure of Benedict's Oxy-Calorimeter:

  • Combustion chamber (for burning sample).

  • Soda lime container (absorbs CO₂).

  • Spirometer (measures O₂).

  • Motor blower unit (circulates gas mixture).

Gross Energy Values

  • 1 g carbohydrate = 4.10 kcal

  • 1 g fat = 9.45 kcal

  • 1 g protein = 5.65 kcal

    • Known as Gross Fuel Values, representing total energy released in a bomb calorimeter.

Physiological Fuel Values (Atwater Bryant Factors)

  • Represent actual energy available post digestion and metabolic losses:

    • Carbohydrates: 4 kcal/g

    • Proteins: 4 kcal/g

    • Fats: 9 kcal/g

  • Fiber burns in the bomb calorimeter but is not utilized by the human body.

Factors Affecting Energy Requirement

Components of Energy Requirement:

  1. Energy for Basal Metabolism (BMR) - basic metabolic processes necessary for survival and health.

  2. Energy for Physical Activity - energy expended for muscle movement.

  3. Thermic Effect of Food - energy released during digestion and metabolism.

Components of Energy Expenditure Breakdown:

  • Basal Metabolic Rate (BMR): 60-65%

  • Physical Activity: 25-30%

  • Thermic Effect of Food: 5-10%

Basal Metabolic Rate (BMR) Overview:

  • BMR: The energy required for involuntary body functions, including:

    • Brain, heart, kidneys, lungs activity.

    • Secretory activities of glands.

    • Peristalsis of the gastrointestinal tract.

    • Oxidation in resting tissues maintaining muscle tone and body temperature.

    • The brain and nervous tissue can utilize more than one-eighth of total energy at the basal state.

Factors Affecting BMR:

  1. Body Composition (muscle vs fat tissue).

  2. Gender (differences in muscle vs fat ratios).

  3. Age (changes in metabolic rate with age).

  4. Body Size and Surface Area (higher surface area = higher energy costs).

  5. Sleep (decreases in basal metabolism during sleep).

  6. Body Temperature (increases BMR with a rise in body temperature).

  7. Endocrine Glands (hormones impact BMR, e.g., thyroid hormones).

  8. Pregnancy (BMR increases in pregnant women).

  9. State of Nutrition (caloric deficit or surplus impacts BMR).

  10. Environmental Temperature (affects metabolic responses, heat production).

  11. Smoking (nicotine elevates BMR).

  12. Genetic Differences (individual variations).

  13. Psychological State (anxiety affecting metabolism).

  14. Pharmacological Agents (substances like nicotine elevate BMR).

  15. Disease Processes (conditions like fever increase BMR).

Thermic Effect of Food (Specific Dynamic Action - SDA)

  • Represents energy cost of digestion/absorption/metabolism.

  • Increases heat production after meal consumption for 1-3 hours.

  • Accounts for approximately 10% of total energy requirement.

Approximate SDA Values:

  • Carbohydrates: ~6%

  • Proteins: ~30%

  • Fats: ~4%

Examples of Thermogenic Foods:

  • L-carnitine, Methionine, Conjugated linoleic acid, L-tyrosine, Caffeine, Chromium, Leucine.

  • Spicy foods, cold exposure, caffeine, and nicotine enhance thermic effects.

Energy Requirement During Physical Activity

  • Accounts for 25-30% of total daily energy expenditure.

    • Includes occupational, discretionary, household, social, recreational, and fitness activities.

Physical Activity Ratio (PAR):

  • Calculated as the energy cost of an activity per minute to BMR cost per minute. Average gives total Physical Activity Level (PAL).

  • Total energy expenditure can be calculated as:

    • In men and non-pregnant women: Total Energy Expenditure (TEE) = BMR × PAL.

Reference Man and Woman Definitions (ICMR)

  • Reference Man: Sedentary male aged 19-39, height ~1.77m, weight ~65kg.

  • Reference Woman: Sedentary female aged 19-39, height ~1.62m, weight ~55kg.

Basic Food Groups (ICMR)

  • Cereals and Products

  • Pulses and Legumes

  • Milk and Meat Products

  • Fruits and Vegetables

  • Fats and Oils

Cereals and Millets

  • Primary energy source in Indian diets (approx. 45% of energy intake).

    • Sources of complex carbohydrates, dietary fiber, B vitamins, and minerals.

Pulses and Legumes

  • Key sources of plant protein; rich in micronutrients when paired with cereals for protein quality.

    • Recommended daily intake: ~85 grams of pulses.

Vegetables and Fruits

  • Provides essential vitamins (A, C, K), minerals, antioxidants, and fiber.

  • Daily intake recommendation: 400g vegetables and 100g fruits.

Milk and Milk Products

  • Excellent sources of protein, calcium, vitamins B12 and D; recommended intake around 300 ml/day.

Nuts, Oil Seeds, and Oils

  • Rich in healthy fats, micronutrients; recommended intake: 27g of fats.

Nutritional Contributions:

  • Cereals: Energy, protein, vitamins, dietary fiber.

  • Pulses: Energy, protein, iron, vitamins.

  • Milk Products: Calcium, protein.

  • Fruits: Energy, vitamins, fiber.

  • Vegetables: Vitamins, calcium.

Balanced Diet Principles

  • Provides all essential nutrients in proper proportions to ensure health.

  • Ideal macronutrient composition:

    • 50-65% calories from carbohydrates.

    • 10-12% from protein.

    • 20-25% from fats.

    • Recommendations to limit fried, processed, sugary foods; increase dietary fiber intake.

Food Guide Pyramid (ICMR-NIN, 2017)

  • Describes proportions and types of food for balanced nutrition.

    • Cereals and Pulses: Largest quantity (carbohydrates, protein).

    • Fruits and Vegetables: Include widely for vitamins and minerals.

    • Meats, Dairy, Oils: Moderate quantities for healthy fats and protein.

    • Processed Foods: Limiting is key for maintaining health.

ICMR-NIN 2000 Kcal Food Pyramid

  • Visual guide on balanced nutrition based on 2000 kcal/day:

    • Portions of cereals, vegetables, fruits, pulses, nuts, oils, and salts outlined to aid dietary balance.

Factors Affecting Food Cost

  • The monetary aspect impacts nutrition management, balancing dietary needs against budget constraints.

  • Influenced by food prices, quality, and consumption patterns; varies regionally with economy and availability.

Determinants of Food Choice

Biological Determinants:

  1. Hunger and satiety signals.

  2. Taste preferences.

  3. Genetics and reward mechanisms.

Economic Determinants:

  1. Food cost and affordability.

  2. Market access.

  3. Economic policies impacting different food types.

Physical Determinants:

  1. Food availability and preparation capabilities.

Psychological Determinants:

  1. Personal beliefs and attitudes.

  2. Learning and conditioning influencing food habits.

Consumer Attitudes:

  1. Taste vs. health tradeoffs.

  2. Sustainability and ethical concerns.

Nutritional Requirements of Adult Man & Woman

  • Nutritional needs based on RDA, including energy requirements based on the reference man/woman.

  • Protein RDA is set at 0.83 g/kg/day; other dietary components outlined including fats, fiber, micronutrients (like calcium, iron, zinc, vitamins).

Dietary Guidelines for Indians (2024)

  1. Variety in diet is crucial to balance nutrition.

  2. Emphasizing vegetables and legumes.

  3. Consuming adequate fruits.

  4. Preference for whole grains as staples.

  5. Sourcing protein from pulses and animal proteins when available.

  6. Moderation in fats/oils; diversity in fat sources.

  7. Limiting salt intake and sweetened foods for health.

  8. Avoiding excessive consumption of processed foods.

  9. Maintaining hydration and safe food practices in cooking and consumption.