Exercise and metabolism

What is metabolism?

Put simply, metabolism is the sum of the chemical reactions that take place within each cell of your body that provide energy for vital processes in order to maintain life.

What is basal metabolic rate (BMR)?

The rate at which your body uses up kilojoules (or energy) to carry out these vital metabolism functions is called the metabolic rate:

• Around five to ten per cent of your energy is used to eat, digest and metabolise food.
• Another 20 per cent goes to burning kilojoules during physical activity (if you are a normally-active person).
• The remaining 50–80 per cent is the amount of energy used while you are at rest. This is known as your basal metabolic rate or BMR. The faster your BMR is, the more efficiently your body burns up kilojoules.

What influences your BMR?

Your BMR can be influenced by many factors including your body size, age, gender, genetic predisposition, hormones and what you eat. The amount of exercise you do can have an effect as well.

How does my gender affect my BMR?

It’s all to do with muscle. Compared to women, men’s bodies generally have more muscle and less fat which makes a difference to your BMR. While fat burns very few kilojoules, muscle is an active, ‘hungry’ tissue that uses up kilojoules even when you’re just sitting around.

How does exercise help increase your BMR?

Exercise increases the amount of muscle you have — and the more muscle you have, the faster your BMR will be. Exercise will generally help increase muscle. Studies show strength training (also known as resistance training or weight training) builds muscle more effectively and increases BMR.

What other factors can influence BMR?

• Genes - the way you use energy can be influenced by inherited characteristics.
• Your age - metabolic rate tends to slow down with age. This is now thought to be related to muscle loss rather than to the ageing process itself.
• Your size - people who are larger tend to burn up more kilojoules.
• Crash dieting or fasting - dramatically restricting kilojoules can trick the body into thinking there’s a famine. This encourages the body to slow down the BMR in order to conserve fat stored in the body.

Tips for boosting your BMR

• Avoid quick weight loss diets or detox diets that cut too many kilojoules – they can slow your BMR down and make it harder to lose weight.
• Even steady weight loss can affect your BMR. At some points, you may hit a ‘plateau’ – a point when weight loss slows down or stops. Increasing physical activity or changing your exercise program may help. Eating a little more may also work, by tricking the body into thinking the ‘famine’ is over.
• Exercise regularly and include two sessions of strength training each week. Building more muscle will boost your BMR.
• Eat breakfast – Some research suggests a relationship between eating breakfast and lowering your BMI, which may happen in part by kick-starting your metabolic rate. But be careful to eat a nutritional breakfast. You can adjust the remainder of your daily kilojoule intake, depending on your needs and goals.
• Some medical conditions such as hypothyroidism (underactive thyroid) can cause weight gain due to a slow metabolism – if you’re concerned, check with your doctor.

Further information

Nutrient Reference Values: Dietary Energy
http://www.nrv.gov.au/energy.htm

Sources

Bouchard C, Perusse L, Deriaz O, Despres JP, Tremblay A. Genetic influences on energy expenditure in humans. Critical reviews in food science and nutrition. 1993;33(4-5):345-50.

Cho S, Dietrich M, Brown CJ, Clark CA, Block G. The effect of breakfast type on total daily energy intake and body mass index: results from the Third National Health and Nutrition Examination Survey (NHANES III). Journal of the American College of Nutrition. 2003;22(4):296-302.

Dolezal BA, Potteiger JA. Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals. Journal of Applied Physiology. 1998;85(2):695-700.

Hensrud D. Slow metabolism: Is it to blame for weight gain? Rochester, MN: Mayo Foundation for Medical Education and Research (MFMER); [updated 2011 Aug 23; cited 2013 June 6]. Available from: http://www.mayoclinic.com.

Metabolism. Melbourne: Better Health Channel; [updated June 2011; cited 2013 June 6]. Available from: http://www.betterhealth.vic.gov.au.

What is metabolism? Tarzana, CA: Metabolic Institute of America (MIA); [cited 2013 June 6]. Available from: http://www.themetaboliccenter.com.

Last Updated: 6 June 2013

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