Episode 13 – Metabolic Adaptation

Key Topics Covered

What Is Metabolic Adaptation? What’s the Difference Between It and Metabolic Damage or Starvation Mode? 

  • Adaptive thermogenesis, is technically defined as the phenomenon of where your TDEE drops by more than you would predict based on body composition change.
  • Metabolic adaptation is another way of saying adaptive thermogenesis. But it as has effects in BOTH directions e.g. TDEE also increases while in a surplus.  
  • Metabolic damage is the proposed phenomenon where even years after chronic dieting, TDEE is still lower than expected. An example of this is The Biggest Loser Study where even 6 years after the show, participants had resting metabolic rates ~600kcal lower on average than what a formula would predict. But this study is a massive outlier. Most research shows that metabolic rate recovers when higher calories are re-introduced.
  • Starvation mode is the concept of where going so low calorie can prevent fat loss because the body “holds onto fat” as a survival mechanism. It is not a thing. But it comes from a grain of truth due to metabolic adaptation. 

What are the Components of TDEE? 

TDEE Components
Image via @aussiesportsnutritionist on Instagram
  • BMR – calories burned at rest. Influenced by body weight, composition, energy availability  
  • NEAT – daily physical activity such as work, house work, incidental movement e.g. fidgeting.
  • EAT – planned/structured exercise, influenced by duration, intensity, frequency and modality.  
  • TEF – Thermic Effect of Food.  

How Does Our Diet Impact our TDEE? 

  • When in a calorie deficit BMR can be reduced by compensations by the body to conserve energy. One example of this is the heart rate slowing down when on lower calories. Another example is disruptions to the menstrual cycle in females when on low calories for prolonged periods of time.
  • If we lose weight and become smaller, BMR reduces as well.
  • NEAT can be subconsciously reduced. People have less energy to do incidental movement. But the even things like fidgetting are reduced noticably.
  • Thermic effect of food is obviously reduced if we eat less food.
  • Exercise calories can be reduced if we do the same work but have less body mass. Obviously this is super variable though since the amount of work we can perform changes.

2020 Study Titled Metabolic Adaptation is Not a Major Barrier to Weight Loss

  • This study concluded that at the 2 year follow up mark post-weight loss that metabolic adaptation was not present. But obviously that lines up with how we think about it. This should not take 2 years to reverse. That would be more along the lines of metabolic damage.  
  • The study also looked at energy expenditure after 4 weeks post diet and found metabolic adaptation only explained ~50kcal difference in energy expenditure. This also makes sense considering this was 4 whole weeks post diet. It likely accounted for a larger difference during and immediately post-diet.  

Practical Relevance of Metabolic Adaptation 

  • Acknowledging that it exists could be helpful. But it likely isn’t the most significant reason someone isn’t losing weight. 
  • If you were in a 500kcal deficit for 12 weeks and you stopped losing weight, metabolic adaptation would not be accounting for that whole 500kcal. 
  • Practically, I would say that metabolic is an argument for using periodic diet breaks.  
Diet Breaks Matador
  • I prefer my clients to take 2 week diet breaks every 8-12 weeks. 
  • This likely helps reverse metabolic adaptation but also gives someone the psychological break from dieting AND can also reduce hunger before starting another round of dieting.  
Diet Breaks

Relevant Resources/Links

Studies Mentioned

Useful Blog Posts