Kilojoules and metabolism

Kilojoules, metabolism and losing weight

Kilojoules are a way to measure energy, just as kilometres measure distance. Understanding the energy content of food and how that affects metabolic rates is the cornerstone of understanding weight loss.

The common term for kilojoule used to be 'calorie'. By definition, a calorie (technically called a kilocalorie or kcal) is the amount of heat required to raise 1 gram of water 1 degree Centigrade. One calorie has the same energy value as 4.186 kilojoules which is now the term accepted internationally. Kilojoules quantify the fuel energy that is available from food and measure the heat output that comes from metabolism, which is the number of kilojoules the body burns.

Metabolism has three major components:

1. resting metabolic rate;

2. physical activity; and

3. kilojoules used to digest and absorb food.

Resting metabolism is the kilojoules used to keep all systems going day in and day out; it is the kilojoules burned by the brain, heart, kidneys and all organs and cells in the body. About two-thirds to three-quarters of the kilojoules we burn every day are accounted for in resting metabolism.

The second component of metabolism is the kilojoules burned in activities such as walking, stair climbing, picking up children and planned exercise. Kilojoules burned in physical activity are the most variable part of metabolism and also the component over which you have the most control.

Finally, a relatively small percentage of kilojoules (about 10%) are burned to digest and absorb food.

The law of thermodynamics

The only scientifically proven method for losing weight involves burning more kilojoules than are taken in. This fact, often called the "law of thermodynamics," has been shown time and time again in decades of rigorous scientific studies. One example of the hundreds of studies that exist was done in Switzerland. Fifty-four obese people had their calories restricted to 1,100 per day. Different combinations of foods and meal timing were tested. There was no difference in weight losses; it came down to the number of calories, not how they were provided, that accounted for the weight loss that the participants experienced.

At the end of the day, the only true way to lose weight is to eat fewer kilojoules in food and/or burn more kilojoules.

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Last revised: Monday, 10 January 2011


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