01 energy metabolism

What is energy metabolism, and which nutrients provide energy?

Energy metabolism is how the body uses, stores and burns energy. The three main energy-providing nutrients are carbohydrates, fats and proteins

What is energy balance, and what are its three states?

• Equilibrium: Energy input = output → no weight change.

• Positive energy balance: Input > output → weight increases. Necessary during pregnancy and growth in infants and children.

• Negative energy balance: Input < output → weight decreases.

Energy input comes from food. Energy output includes digestion, metabolism, nutrient transport and physical activity.

Why is maintaining energy balance important? It contributes to health and well-being and helps prevent common health problems, including obesity.

What is calorimeter, and what are its three main methods?

Calorimetry measures heat production or energy expenditure.

• Bomb calorimetry: Measures food energy by burning food in a calorimeter.

• Direct calorimetry: Measures energy expenditure through the heat produced by the body.

• Indirect calorimetry: Estimates energy expenditure by measuring oxygen consumption and carbon dioxide production.

What are the energy units and conversions?

1 kcal = 1 nutritional Calorie (Cal).

1 kcal = 4.184 kJ.

1 kcal is the heat required to raise the temperature of 1 kg of water by 1°C.

How much energy do nutrients provide per gram?

Nutrient - Energy measured in a calorimeter - Metabolizable energy in the body

Carbohydrates 4.1 kcal/g 4 kcal/g

Fats 9.4 kcal/g 9 kcal/g

Proteins 5.6 kcal/g 4 kcal/g

Alcohol 7.0 kcal/g 7 kcal/g

Fiber No calories listed —

How do you calculate daily calorie intake from macronutrients?

Multiply the grams of each nutrient by its metabolizable energy value, then add the results.

Example:

585 g carbohydrates × 4 = 2,340 kcal

150 g protein × 4 = 600 kcal

110 g fat × 9 = 990 kcal

Total = 3,930 kcal/day.

What is the respiratory quotient, and how is it calculated?

The respiratory quotient compares the volume of carbon dioxide produced with the volume of oxygen consumed.

What are the RQ values for different nutrients?

Carbohydrates: 1.0

Fats: 0.7

Proteins: 0.8

Mixed diet: 0.85

Examples from the PDF:

Glucose: RQ = 6/6 = 1.0.

Palmitic acid: RQ = 16/23 ≈ 0.7.

What does an RQ greater than 1.0 indicate?

It indicates that carbohydrate oxidation is favored over fat oxidation.

What is daily energy expenditure?

Daily energy expenditure consists of four components:

DEE= BMR+physical activity+thermic effect of food+thermogenisis

What is basal metabolic rate (Grundumsatz), and what does it include?

BMR is the energy expenditure of a person mentally and bodily at rest, in a thermoneutral environment, 12–18 hours after a meal.

It supports:

• Functioning of the lungs, heart, kidneys and brain.

• Maintenance of ionic gradients.

• Metabolic reactions.

For a sedentary person, BMR accounts for approximately 60–70% of total energy expenditure.

Factors affecting BMR

Increase

• Lean body mass

• Larger surface area

• Sex (M > F)

• Body temperature: in fever 30-35% á at 40˚C (104oF)

• Nervous sytem activity (release of norepinephrine)

• Hormones, esp. Thyroid hormone

• pregnancy and lactation

Decrease

• Low calories intake

• Aging

What is a resting metabolic rate, and how does it differ from BMR?

RMR is measured when a person is not fasting or completely rested.

According to the PDF, RMR is typically about 6% higher than BMR.

What are the four steps of respiration shown in the diagram?