Energy in Food

Defining Calories

Energy in food is a fundamental concept in nutrition, as it determines how food supports bodily functions and activities. The measurement of energy in food is expressed in calories, which are derived from the chemical breakdown of nutrients.

• Metabolism: The set of chemical reactions that break down and use food molecules to release energy.

• Energy released from food through metabolism is measured in calories.

There are several units related to calories:

• Calorie (cal): The amount of energy needed to raise 1 gram of water by 1°C.

• Kilocalorie (kcal): Equal to 1,000 calories. This is the unit commonly used in nutrition to express the energy content of foods.

• Calorie (with a capital 'C'): In nutrition, "Calorie" (capitalized) is used interchangeably with "kilocalorie" (kcal).

Example: 2,000 Calories (kcal) is enough energy to raise two 2-liter bottles from freezing to boiling.

Note: This course will always use "Calories" or "kcal".

Relationship Between Units

• 1 kilocalorie (kcal) = 1,000 calories (cal)

• 1 Calorie (with a capital 'C') = 1 kilocalorie (kcal) = 1,000 calories (cal)

Calculating Calories in Food

Energy Contribution of Macronutrients

Different macronutrients provide different amounts of energy per gram. Understanding these values is essential for calculating the total energy content of foods.

• Carbohydrates: 4 Calories per gram

• Proteins: 4 Calories per gram

• Fats: 9 Calories per gram

• Alcohol: 7 Calories per gram (not a nutrient, but provides energy)

To determine the total Calories in a food, multiply the grams of each macronutrient by its respective energy value.

Example Calculation

In 30g of cheese:

Formula:

Nutrition Label Calculations

Nutrition labels provide the mass of each macronutrient per serving. Use these values to calculate the total Calories per serving.

Calculation:

• Carbohydrates: Calories

• Fats: Calories

• Proteins: Calories

• Total Calories: Calories

Comparing Foods by Caloric Content

To compare foods, use the nutrition label data to calculate and contrast total Calories per serving.

Example: Food #2 has more total Calories per serving than Food #1.

Summary Table: Calories per Gram of Macronutrients

Additional info: Alcohol is not considered a nutrient but does contribute energy. The calculation method for Calories is foundational for understanding food labels and dietary planning.