Factor in the resting metabolic rate while trying to burn off energy
‘ IT must be my metabolism’’ is a phrase I often hear in practice as clients search for an explanation to the sometimes frustrating experience of aiming to change their weight and improve their health.
But to what extent can a person’s metabolic rate be to blame for their current weight status? After testing the resting metabolic rate of hundreds of clients over the past few years, experience shows it can make a huge difference.
Resting metabolic rate is the amount of energy a person burns up at rest just to keep their body alive, including the energy needed for functioning of vital organs, breathing, circulation and contractions of the gastrointestinal tract.
Resting metabolic rate accounts for 60-70 per cent of a person’s total daily energy needs, and as a result, a change to this can mean a significant change in weight over time.
For example, research in the Journal of Clinical Endocrinology and Metabolism (1997;82(10):3208-3212) shows that resting metabolic rate decreases by about 10 per cent in post-menopausal versus pre-menopausal sedentary women.
If a woman in this age group ate the same amount of kilojoules over the next 10 years without adjusting for a lower resting metabolic rate, they would gain around 10kg a year.
Resting metabolic rate combined with an estimate of how many kilojoules a person burns daily through activity and exercise, enables a reasonably precise measure of total daily kilojoule requirements to be made.
This in turn assists with how much a person needs to eat in a day for weight maintenance, weight loss or weight gain.
While it’s commonly believed that overweight people have a ‘‘ slow metabolism’’ and thin people who can eat the side of a house and still not put on weight have a fast metabolism, the opposite is more often the case.
The lighter you are, the less energy your body needs daily in order to keep it functioning, while the heavier you are, the harder your body has to work and the higher the number of kilojoules you will need in a day.
However, resting metabolic rate is just one component of a person’s total daily energy needs — the remainder being made up of the thermic effect of food (energy used during digestion to absorb, transport and metabolise food) plus physical activity. Generally, around 10 per cent of daily energy requirements are used up during digestion.
The third component of total energy expenditure, physical activity, is the most variable and the resulting influence on total energy needs for the day can range from quite small (sedentary people) to significant (athletes).
Resting metabolic rate can be affected by a number of factors, and those that increase metabolism include a higher body weight, a higher amount of muscle in the body, younger age, male gender, nicotine, caffeine, illness and stress.
Factors that decrease resting metabolic rate include lower body weight, female gender, higher percentage body fat, older age, weight loss and kilojoule restriction. Certain medications can also increase or decrease resting metabolic rate.
Most people would like a higher resting metabolic rate as this means you can eat more and not gain weight.
So to keep your metabolism ticking along, the best advice is to exercise regularly, particularly including activities that assist with the gaining of lean muscle tissue, and to avoid very low kilojoule diets.
If you’re aiming to lose weight, do so gradually and ensure you include regular exercise to assist with retention of muscle tissue.
To burn more kilojoules overall, it’s also important to eat regularly so you keep your digestion system working for you in more ways than one.
Sharon Natoli is an accredited dietitian and director of Food & Nutrition Australia.