Metabolism and Weight Loss: The Facts

What is my Metabolism?

Your metabolism is the sum of all biochemical processes that happen in the body. It is the energy required to keep you functioning each day. Examples include breathing, moving, digestion etc. Your metabolic rate is dynamic in nature meaning that no two people are the same. Some individuals will burn a lot of energy (calories) in 24 hours whereas others will burn very little.

What is it made up of?

  1. BMR: Basal Metabolic rate

This is the energy used for essential activities performed by the body at rest. Example:  Energy used by the organs, tissues, brain. This makes up 60-70% of energy needed daily. Age weight, height and gender can all influence BMR.

  1. NEAT: Non-Exercise Activates Thermogenesis.

This is the energy used for daily activities but does not include planned exercise. Example: Energy used working.

  1. TEF: Thermic Effect of Food.

The body will use energy to break down food that is consumed. Energy is required for transport, breakdown and absorption. TEF can be influenced by the type of food consumed. For example, protein has the highest energy cost.

  1. EAT: Exercise Activity Thermogenesis.

This relates to planned daily exercise. Examples could be running or weight training. This component is the most variable and specific to an individual. Heart rate monitors such as the MyZone  MZ-3 can be used to track EAT.

Why does it matter?

When a person decides they want to lose weight, one of the main strategies used is a reduction of calorie intake. However, long-term underfeeding challenges the body and can cause a defence reaction. This reaction involves the slowing down of the metabolism to protect energy stores and preserve body mass. So, you may be eating less calories than you used to but you are also burning less throughout the day. The scientific name for this is Adaptive Thermogenesis. Unfortunately, this phenomenon is usually combined with an increase in appetite and food palatability. This process may explain why some people struggle to lose weight after a certain point and why weight regain is so common.

What can I do?

To avoid having your metabolism slow down while dieting you should slowly reduce calorie intake each week. In the fast paced world we live in, we often look for a quick fix and go to extreme lengths to lose weight fast buy adopting a dramatic reduction in calorie intake. A big drop in calories could cause a significant loss in calorie burning muscle mass and may cause the defence reaction mentioned above. To avoid rapid fat regain once your diet ends, again, slowly increase your calories. It may also be a good idea to put the diet on hold for a day or two during the week. This gives your body a chance to replenish its energy stores and it also gives you a psychological break.

Most people can experience significant weight loss in a short space of time but very few have the know how or will power to keep it off long term. Knowing how your metabolism works may be one strategy to help with this common issue.


  • Levine, J.A., 2005. Measurement of energy expenditure. Public health nutrition, 8(7a), pp.1123-1132.
  • Tremblay, A., Royer, M.M., Chaput, J.P. and Doucet, E., 2013. Adaptive thermogenesis can make a difference in the ability of obese individuals to lose body weight. International journal of obesity, 37(6), p.759.
  • Trexler, E.T., Smith-Ryan, A.E. and Norton, L.E., 2014. Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition, 11(1), p.7.