4.1

NATS1560: Understanding Food - Week 2, Energy Part 1

• Learning Objectives:
  • Explain the equivalence between energy and heat, and the primary function of food as fuel for the body.
  • Define the measurement units of food energy (kilocalories/calories).
  • Explain the difference between gross and metabolizable energy of food.
  • Define standard metabolizable energy values of macronutrients (Atwater Values).
  • Apply the 4-9-4 rule to estimate metabolizable energy.
  • Critically assess the accuracy of Atwater Values and use Modified Atwater Values.
  • Define and use the Acceptable Macronutrient Distribution Ranges (AMDR) or Dietary Reference Intakes.

Human Nutritional Needs (Review)

• Humans are omnivores, needing a variety of foods.
• Nutrients are pure substances providing nourishment.
• Nutrition science recognizes six categories of nutrients for human nutrition: proteins, carbohydrates, and fats (These are macronutrients, needed in larger quantities).
• Other nutrients (micronutrients) include water, minerals, and vitamins (a seventh category, phytochemicals, is currently under study).

Why Do We Need Food?

• Our bodies need food for matter (atoms) for growth, repair, and function of organs and tissues.
• Food is needed for energy (capacity to do work).
• Food is the source of matter and energy for the organism.
• Metabolism involves physical and chemical processes to/from food for internal function in organisms.

Metabolism

• Metabolism is a complex process.
• Diagrams of the chemical pathways show the complexity of energy production from food.

Food Energy

• Energy exists in different forms (kinetic, thermal, chemical).
• Living organisms extract chemical energy from food molecules through cellular respiration.
• Cellular respiration breaks down food molecules, produces ATP molecules (energy), and releases heat, water vapor (H₂O). carbon dioxide (CO₂).

Kilocalories and "Calories"

• Kilocalorie is a unit of energy to raise the temperature of 1 kg of water by 1°C at standard atmospheric pressure.
• 1 kilocalorie = 1000 calories.
• In nutrition, food energy is commonly measured in kilocalories (kcal), or food calories.

How Much Energy Do We Need?

• Estimated Energy Requirement (EER) is energy intake needed for maintaining body weight.
• EER depends on factors like height, weight, composition (muscle/fat), age, physical activity levels, and health conditions.

Does Food "Become" Energy?

• Food does not "become" energy.
• Food is the source of matter and energy for the body, but the energy is neither generated nor destroyed; it is transformed and used.

Does Body Weight "Become" Energy?

• Weight is proportional to mass.
• Losing weight usually means losing mass.
• Metabolic processes cannot transform mass into energy.

Review

• Questions about the need for food, the transformation of food into energy, the process of cellular respiration, units for measuring food energy, and alternative names for the food calorie.

Cellular Respiration

• Three processes involved in cellular respiration: glycolysis, Krebs/Citric Acid Cycle, and Electron Transport Chain.
• Glycolysis is an anaerobic process that converts glucose to pyruvate to ATP.
• Krebs/Citric Acid Cycle is an aerobic process that converts pyruvate to ATP through a multi-step process.
• Electron transport chain is an aerobic process that converts the energy from NADH and FADH₂ to ATP.

Measuring Energy in the Body

• Energy is released and made available through cellular respiration.
• The "calorie" unit is used to measure heat.
• In food, "calories" are actually kilocalories (1000 calories).

How Much Energy Does Food Provide?

• Only macronutrients (carbohydrates, fats, proteins) provide energy for the body.
• Metabolizable energy formula involves energy from each macronutrient and energy losses from digestion and excretion.
• Atwater values are standard metabolizable energy for each macronutrient per gram.

The 4-9-4 Rule

• A simple method to calculate energy from food by using percentages of Atwater values.

How Accurate are the Standard Energy Values?

• Standard energy values for carbs, proteins, and fats are averages.
• Modified Atwater values provide slight improvements on the approximations.

Review (2)

• Questions about various nutrients, how much energy they provide, and percentages for macronutrients.

How Many Calories in a Food?

• Application of the 4-9-4 rule to calculate the calories from a chocolate chip cookie.

Macronutrient Distribution

• Dietary Reference Intakes (DRIs) outline the percentage of carbohydrates, proteins, and fats for healthy diets across different age groups.
• Carbohydrates are the body's primary energy source.

Macronutrient Distributions (Using Standard Values)

• Calculation of the percentage of energy from various food sources through the 4-9-4 rule.

Review (3)

• Questions about the acceptability of a diet based on certain foods (e.g., cookies, bananas), the association of a diet with reduced risk of chronic diseases, and the energy provided by various items (coffee).