Written by Master Coach, Kimberley Leggett
Does losing weight slow down metabolism? Absolutely. Does metabolism decrease more than expected? It depends!
Metabolic adaptation is the process by which the body alters how efficient it is at turning the food you eat into energy1. It is an evolutionary biological process in response to starvation which when we look at it through the prism of our prehistoric ancestors, makes a lot of sense! If food was abundant this meant starvation was unlikely and therefore there was no need for the body to store calories as fat for later use. In times of famine, it was essential for one’s metabolism to be extremely efficient and only use a minimal amount of calories to maintain biological homeostasis as the rest must be stored as fat for later use to prevent starvation.
From this understanding of metabolic adaptation in terms of starvation – we can apply this to dieting!
To understand metabolic adaptation, we must first understand the elements that effect it including TDEE (Total Daily Energy Expenditure) and its components.
TDEE (Total Daily Energy Expenditure), which is the total amount of calories burned in a day, is compromised of exercise activity thermogenesis (EAT), non-exercise activity thermogenesis (NEAT), thermic effect of food (TEF) and your resting metabolic rate (RMR). During phases of dieting, your TDEE changes. This is your body’s way of manipulating its role in energy conservation so if you have less calories available you will burn less and your body will prioritise its highest needs first – metabolic functions etc.
Remember that metabolic adaptation is a response to starvation, but in modern times, dieting is the closet we’ll ever get to famine. This is therefore why your body recognises this net decrease in calories from dieting and perceives it as starvation. When this occurs, your TDEE, BMR, NEAT and EAT decrease as your body becomes more calorically efficient. This is why an individual can maintain a caloric deficit for a week weeks, lose weight then plateau while eating the same amount of calories.
In the fitness industry, this type of phenomena has often been associated with the term ‘metabolic damage’ but the main difference between metabolic damage and adaptation is that “damage” suggests that there is an irreversible issue whereas adaptation indicates the body is making an adjustment. Despite what you may have heard – no, losing weight does not “damage” your metabolism!
The physiology of weight loss is complicated, but the best strategies for losing fat and keeping it off don’t have to be! Understanding what metabolic adaptation is can help us better understand how we can achieve better body composition results in the long-term whilst highlighting the importance of strategies such as diet-breaks, refeeds and the reverse dieting can help keep energy expenditure higher and thus make the dieting process easier!
Want to learn simple, evidence based systems and in-depth knowledge you can implement with clients to help them maximize their fat loss, hypertrophy, body recomposition, performance or competition prep goals? Enrol into the Ultimate Physique Science Bundle by Dr Layne Norton (includes the Science of Nutrition & Training the Physique Athlete online courses!).
- Hall, K.D. (2018). Metabolic adaptations to weight loss. Obesity (Silver Spring), 26 (5), 790-791. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6086582/
- Norton, L. (PhD). (2019). The Science Of Nutrition. Clean Health Fitness Institute. 3. Woodburn, B. (2019). What is metabolic adaptation? Retrieved from: https://www.mindpumpmedia.com/blog/what-is-metabolic-adaptation