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What are nutrients and why do we need them?

Healthy eating is a choice – your choice. And before you can fully explore that choice, it helps to have a bit of an understanding about what food actually is and what it delivers to your body.

Food and drinks are made up of a range of substances called nutrients that we use for growth, maintenance of healthy tissues and energy. Good nutrtition not only allows us to function well physcially, but mentally as well.

Nutrition is the study of nutrients and the way we process them. Nutrients fall into two main categories: macronutrients,that we need in relatively large amounts; and micronutrients, which are mostly needed in minute amounts.

Nutrients that the body can make itself, although they may also come from the diet, are considered nonessential. An essential nutrient, however, is one that we can’t make for ourselves in sufficient quantities to meet our needs, so must be obtained from food. These nutrients include minerals, most vitamins, some amino acids (from which proteins are made) and some fatty acids. Because we can’t make these, we must regularly choose foods that supply them.

Lack of nutrients

This can result in various deficiency diseases or other disorders. Eating more macronutrients than you need can lead to obesity and related disorders, and excess intake of micronutrients can be toxic, sometimes even fatal. Also, the balance of various types of nutrients, such as how much unsaturated vs saturated fat is consumed, can influence the development of disorders.


Some people choose to take supplements to increase their vitamin and mineral levels – and in some circumstances this may be sensible. Studies looking into the value of supplementation are ongoing, and theories about the worth of supplements come and go. There are some studies that suggest taking too many supplements may be harmful. Read our Take care with supplements page.


Macronutrients make up the bulk of our diet and are mainly involved in the supply of energy, but are also responsible for other activities.

Macronutrients include
  • carbohydrates
  • proteins (including essential amino acids)
  • fats, or lipids (including essential fatty acids)
  • water.

We need energy for everything we do, including digesting our food, keeping our body tissues working so we can do things like use our muscles, control our temperature, grow and make new tissues. Energy is released from carbohydrates, proteins, fats and, to a lesser extent, alcohol, by a process called oxidation.

The unit of energy is the kilojoule (kJ). Fats yield 37.7 kJ/g; proteins 29.3 kJ/g [1] and carbohydrates 16.7kJ/g. Alcohol yields 29.3 kJ/g.

Our personal energy requirements vary with age, gender, body size and activity – so there are different recommendations of how much energy is needed every day for each age and gender group.

Men Sedentary kJ  Moderate Activity kJ 
19-30 years 10,800    13,800
31-50 years 11,000 16,100
51-70 years 9,500 12,100
>70 years 7,400 13,600

Women  Sedentary kJ  Moderate Activity kJ 
19-30 years 8,100 10,500
31-50 years 7,900 10,100
51-70 years 7,600 9,600
>70 years 7,100 9,100

Source: NRV NZ and Australia, 2005


Micronutrients are substances we must get in small quantities from our diet, either because we can’t make them for ourselves or because we can't make them as fast as we need them. They are not used as energy sources, but are necessary to process energy so our cells can use it.

Micronutrients include
  • vitamins, which are organic compounds (made from carbon)
  • minerals which are inorganic (not made from carbon).
Next: Vitamins top back

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