Energy requirements and diet imbalances

In a nutshell

All organisms need energy, but too much or too little of any nutrient can cause problems in the body. In this lesson, you will explore the effects of different imbalances on the body and compare how energy requirements differ based on different factors.

Energy

Humans obtain energy from the food they eat and energy is needed by every cell. Energy can be measured in kilojoules $(kJ)$ and the amount of energy humans need to stay alive is called their 'basic energy requirement' (BER).

Calculating daily basic energy requirements

Humans use an average of $5.4\space kJ$ of energy per kilogram of body weight each hour. Daily basic energy requirements can be calculated using this equation:

$Daily\,BER\,(kJ/day) = 5.4\times 24\, (hours)\times body\,mass\,(kg)$

Example

What is the daily basic energy requirement (BER) of a boy that weighs $50\space kg$ ?

Calculate the average amount of energy used in a day:

$5.4\times 24\,(hours)\,=129.6\,(kJ)$

Multiply the answer by weight in kilograms:

$129.6\,(kJ)\times\,50\,(kg) =\,\underline{6480}\,(kJ)$

$\underline{Therefore,\ the\ daily\ BER\ is\ 6480\ kJ/day}$ .

Factors affecting energy requirements

Energy requirements differ based on the factors discussed in the table below.

Factor	Effect on energy requirements
Increased body weight	More body weight means more cells in the body, this means that more energy is needed.
Increased activity	More activity means more energy is used by cells which means that BER will be higher.

Tip: Pregnancy, gender, age and occupation can all affect body weight and activity level and therefore affect energy requirements.

Example

What is the daily BER of someone weighing $60\space kg$ , who also burns $376\space kJ$ of energy through swimming every morning?

Calculate the average amount of energy used in a day:

$5.4\times 24\,(hours)\,=129.6\,(kJ)$

Multiply the answer by weight in kilograms:

$129.6\,(kJ)\times\,60\,(kg) =\,7776\,(kJ)$

Add the daily BER to the $kJ$ of energy burned through swimming:

 $7776\,(kJ)\, +376\.(kJ)\,=\,\underline{8152}\,(kJ)$

$\underline{Therefore,\ the\ daily\ BER\ is\ 8152\ kJ/day}$ .

Health problems

Obesity

Excess energy intake or inadequate activity can lead to obesity. This is because energy taken in from food that is not used up is stored. Over time, this can cause weight gain and lead to health complications like heart disease and stroke.

Starvation

Starvation causes reduced energy intake which can lead to weight loss. This is because the body uses up stored energy when insufficient energy is taken in. Consequences may include slow growth in children and irregular periods.

Deficiencies

Vitamins and minerals are micronutrients needed in small amounts to maintain health. A lack of any nutrient can be harmful to health because the body may not be able to make it on its own.

Nutrient	deficiency disease	Symptoms
Vitamin C	Scurvy	Bleeding gums, tiredness and joint pain.
Vitamin D	Osteomalacia	Bone pain, frequent fractures and muscle weakness.
Iron	Iron deficiency anaemia	Tiredness, dizziness and breathlessness.