Metabolism and weight loss

Metabolism is the process of your body converting the food you eat to the energy you need for every day activities and exercise.

The metabolic process takes the calories from the carbohydrates, fats and proteins that you eat, combines them with oxygen to release energy.  This energy allows your body to function.

Daily energy expenditure falls into three categories, namely:

  1. basic needs (breathing, walking, talking etc)
  2. food processing (digestion)
  3. physical activity

 1 Basic Needs

Even when your body is at rest, there are still biochemical processes occurring that require energy to drive them.  Think of an idling car – it’s not going anywhere but still needs fuel to keep running.  Your body is the same – while you are sleeping, your body is still breathing, pumping blood and repairing.

The energy expenditure for this basic functioning is the basal metabolic rate (BMR).  It can account for as much as 70% of your daily energy expenditure.

There are numerous BMR calculators online – you will need your weight (kg), height (cm) and age to work out your BMR.

Once you have calculated your BMR, you can multiply it by a factor of 1.2 – 1.7 depending on your level of activity to get your daily calorie allowance.

Example 1:

For an inactive office worker, use a factor of 1.2

BMR = 1500 cal x 1.2 = 1800 cal per day to maintain weight

Example 2:

For an active person (5-6 1 hour gym sessions per week; mothers; manual labourers), use a factor of 1.7

BMR = 1500 x 1.7 = 2550 cal per day to maintain weight

2 Digestion

Digesting the food you consume is a labour intensive process for your body – almost ten percent of the calories you eat each day are spent maintaining digestive processes.

3 Exercise and physical activity

Finally, all physical activity, such as running, swimming or walking, also requires calories.

So, how can this help me?

You can’t control the basic and digestive needs of your body, but you can control how much physical activity you do.

So, if you want to lose weight (i.e. burn extra calories) – get out there and exercise!

The amount of calories you burn when exercising depends on a number of factors including:

  • Genetics – some people have a naturally higher metabolic rate
  • Diet – starvation or a period of deprivation can slow your BMR by as much as 30%
  • Age – older people have a slower metabolic rate and tend to have less muscle which is the active calorie burning tissue.
  • Gender – sorry ladies, but the fact is we burn less calories than men when performing equivalent exercise.  The reason for this is that men tend to have more muscle mass.
  • Body composition – larger people burn calories at a higher rate than smaller people, because more energy is required to move their bodies.
  • Exercise intensity also influences the number of calories you burn – generally speaking the harder the exercise, the more calories burnt.  High impact exercise also burns more calories than a lower impact workout.

To loose weight, you try aiming to burn 500 – 600 cal per workout.

Get out there, get fit and have fun!  Your body will thank you for it.

Remember, always talk to a GP before undertaking a new exercise


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