Metabolism refers to all the processes in your body that help you to function normally. The rate at which your body uses up kilojoules (or energy) to carry out these vital processes is known as your metabolic rate. You use 50–80 percent of your energy while you are at rest — this is your basal metabolic rate (BMR). The faster your BMR, the more efficiently your body burns up kilojoules.
Factors that can influence your BMR
- How much muscle you have. Muscle is active tissue that uses up more kilojoules even when you’re just sitting around. The more muscle you have, the more kilojoules you burn. This explains why men — whose bodies tend to have more muscle — generally lose weight more easily than women.
- Your age. Metabolic rate tends to slow down with age. This is now thought to be related to muscle loss rather than the ageing process itself.
- Your size. People who are larger tend to burn up more kilojoules.
- How warm or cold it is. The cooler the temperature, the more kilojoules your body burns to try and stay warm
- Weight loss. To understand why losing weight can slow down metabolism, it helps to understand that your body can’t distinguish between a diet and a famine. Humans didn’t evolve in an environment full of food outlets, but rather in an environment with uncertain food supply. We might live in the 21st century but as far as your body is concerned you’re still a hunter-gatherer. Dramatically reducing the amount of kilojoules you eat or dramatic weight loss sends a signal to your body that there’s a lack of food. Your BMR then slows down to conserve fat and ensure survival.
Tips for boosting your BMR
- Avoid crash diets, quick-weight-loss diets and fasting — they will slow down your BMR, making it harder to lose weight.
- Even steady weight loss can sometimes affect BMR. At some point, you may hit a ‘plateau’ — when weight loss slows down or stops. Increasing the amount of physical activity you do or changing your exercise program may help. Eating a little more may work too by tricking the body into thinking the ‘famine’ is over.
- Get regular exercise and include two sessions of strength training each week. Strength training exercises help you build muscle, and building more muscle should help boost your BMR.
- Eat breakfast — research from the Third National Health and Nutrition Examination Survey (NHANES III) suggests a relationship between eating breakfast and lowering your (BMI), which is an indication of whether you’re a healthy weight for your height. This relationship is believed to happen in part by kick-starting your metabolic rate.
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
Better Health Channel: Metabolism explained http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Metabolism_explained
Sources
Cho S Dietrich M Brown C et al. 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 & endurance training influence BMR in non-dieting individuals. Journal of Applied Physiology. 1998; 85: 695-700.
Hensrud D. Slow metabolism: Is it to blame for weight gain? [online] Mayo Foundation for Medical Education and Research. c1998-2010 [last updated 27 Aug 2009, accessed 17 Aug 2010] Available from: http://www.mayoclinic.com/health/slow-metabolism/AN00618
