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diet and kilojoules

Food supplies kilojoules which are units of energy. The body burns kilojoules to stay alive and to move. Kilojoules are a way of measuring the potential energy in foods. They also measure the amount of energy the body uses. There are only 3 nutrients that provide kilojoules in food: fat, protein, and carbohydrate. These 3 nutrients make up foods in all of the major food groups. Some foods have 1, 2 or all 3 of these nutrients. Even though it is not a nutrient, alcohol has kilojoules too.

How does the nutrient affect the body? 
All 3 of these nutrients: carbohydrates, proteins, and fats, provide kilojoules or energy to the body. These nutrients are released from foods during digestion. Then they are absorbed into the blood stream and changed to glucose or blood sugar. Glucose is what the body actually uses as energy. Energy that the body does not need right away gets stored. Some is stored as fat and some can be stored in the liver and muscles as glycogen, called stored glucose. The body can use these stores at a later time.

Each nutrient provides different amounts of kilojoules to the body.
  • One gram of carbohydrate provides 16 kilojoules
  • One gram of protein provides 17 kilojoules
  • One gram of fat provides 37 kilojoules
  • One gram of alcohol provides 29 kilojoules
These figures are used to calculate kilojoules per serving. If a food is made of only fat, which contains 9 grams of fat, the kilojoules in the product equals: 9 grams fat x 37 kJ/gram of fat = 333 kilojoules.

Food offers more than just kilojoules. It offers vitamins, minerals, and water, which are also very important nutrients. These nutrients do not supply kilojoules. When foods supply mainly kilojoules and few nutrients, they are known as "kilojoule-dense." When foods supply kilojoules along with vitamins and minerals, they are known as "nutrient-dense." The key is to choose your kilojoules wisely. Choose foods that will provide kilojoules but also important nutrients like vitamins and minerals.

For a healthy diet, people need all 3 nutrients in their daily diet. The dietary guidelines for Australians encourage the consumption of more whole grain products, fresh vegetables and fruits, and dry beans (legumes).

The Australian Guide To Healthy Eating acts as a tool to help individuals follow the Dietary Guidelines. In addition, health experts recommend a diet where kilojoules come from
  • 50 to 60% of carbohydrates
  • 30% of fat (with 10 % from saturated fat) for adults
The body's need for energy and fuel never stops. Each individual person requires a certain amount of kilojoules to fuel their body. The amount of kilojoules depends on many factors. These include:
  • weight
  • height
  • basal metabolic rate, or BMR, which is how many kilojoules the body burns at rest in 24 hours
  • age
  • body composition, or how much fat and muscle the body has
  • physical condition and activity level
Once adulthood is reached, energy needs or kilojoule needs drop 2% for each decade. Eating more than the required kilojoules usually results in weight gain. Eating less than the required kilojoules usually results in weight loss.

Active men and teenaged boys need approximately 9000 - 13,500 kilojoules to fuel their bodies properly. Again this is only an estimate. Kilojoule needs in the diet should be figured on an individual basis. Following the Australian Guide To Healthy Eating, for this group, 11,000 kilojoules would be about:
  • 6 servings from the bread group
  • 7 servings of vegetables
  • 3 servings of fruit
  • 3-5 servings from the milk group (teens should have 5 servings)
  • 1-2 servings (for a total up to 200 grams) from the meat group
Active women, teenaged girls, children, and most men need approximately 9200 kilojoules to fuel their bodies properly. Following the Australian Guide To Healthy Eating, for this group, 9200 kilojoules would be about:
  • 5 servings from the bread group
  • 6 servings of vegetables
  • 3 servings of fruit
  • 2-3 servings from the milk group (pregnant and breastfeeding women should get 2 servings, teenaged girls and young adults to age 18 should get 3-5 servings)
  • 1.5 servings (for a total of 100 - 150 grams) from the meat group.
Women and some older adults need approximately 6500 - 9300 kilojoules to fuel their bodies properly. Following the Australian Guide To Healthy Eating, for this group, 6500 kilojoules would be about:
  • 3 servings from the bread group
  • 4 servings of vegetables
  • 2 servings of fruit
  • 2-3 servings from the milk group
  • 1 - 1.5 servings (65 - 150 grams) from the meat group

Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne

Last Updated: 30/11/2004
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.

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