Nutrition and Energy

This lesson covers: 

  1. Why we need energy from food
  2. Health issues from too much or too little energy intake
  3. Calculating basic energy requirements

Why our bodies need energy

Our bodies require a steady flow of energy to function properly, which is obtained from the food we consume so it's crucial to eat a balanced diet.


Energy is required for:

  • Brain and nerve function - To process information and control the body.
  • Muscle contraction - To allow movement.
  • Maintaining body temperature - To keep a stable internal environment.

Health consequences of energy imbalance

An imbalance in energy intake can lead to various health issues.

It's essential to maintain an energy balance to support overall health.

Consequences of surplus energy intake

Fast food meal with burgers, fries, and chicken nuggets.
  • Obesity - It leads to unnecessary fat accumulation.
  • Raised disease risk - Diseases like diabetes and heart disease are more likely due to excessive fat.

Consequences of insufficient energy intake

Empty plate with a question mark in the centre, surrounded by a fork and knife.
  • Impaired growth and development in children - This affects physical and mental capabilities.
  • Increased infections - A weakened immune system makes the body more susceptible to illness.
  • Irregular menstrual cycles in biological females - This affects reproductive health.
  • Nutrient deficiency diseases - Diseases like scurvy (vitamin C deficiency) and rickets (vitamin D deficiency) are more common.

Different energy requirements

The amount of energy an individual needs daily varies depending on several factors, including body size and composition.

Illustration showing different energy requirements for an athlete on a bicycle, an elderly person with a cane, and a pregnant person.
  1. Activity level - The more active you are, e.g. if you're an athlete, the more energy you need.
  2. Age - Teenagers often need a lot of energy because they're growing, whereas elderly people need less.
  3. Pregnancy - Pregnant people need more energy because the baby growing inside them requires a lot of energy.
  4. Body mass - The bigger you are the more cells you have and each cell requires energy.

Calculating basic energy requirements (BER)

The basic energy requirement (BER) provides an estimate for the energy needed for bodily functions at rest


The BER formula is:

BER (kJ/day) = 5.4 × 24 hours ×mass (kg)


As body mass increases, the BER also increases, as a larger body has more cells that need energy.


Additionally, extra energy is required for any physical activity undertaken throughout the day.

Worked example - Calculating basic energy requirements (BER)

Calculate the BER for a person weighing 60 kg.


Step 1: Equation

BER (kJ/day)= 5.4 × 24 hours × mass (kg)


Step 2: Substitution

BER (kJ/day) = 5.4 × 24 × 60


Step 3: Correct evaluation

BER = 7,776 kJ/day