Episode 107 – Why Your Calorie Intake Changes Your Calorie Expenditure

Key Topics Covered

Total Daily Energy Expenditure Model

Components of Energy Expenditure  

  • Resting Metabolic Rate (RMR) – Calories burnt at rest.
  • Thermic Effect of Food (TEF) – Calories burnt digesting, absorbing and metabolising food.
  • Non-Exercise Activity Thermogenesis (NEAT) – Calories burn through incidental movement e.g. fidgeting, talking, housework etc.
  • Exercise Activity Thermogenesis (EAT) – Calories burnt through planned exercise.

Individual Variation in a Calorie Surplus

  • 12 pairs of twins were overfed by 1000kcal per day, 6 days a week, for a total of 84 days during a 100-day period. 
  • On the seventh day of each week, they consumed the baseline number of calories. 
  • Physical activity was controlled by solely doing a 30-minute walk each day.
  • Weight gained varied from 4.3kg to as much as 13.3kg.
  • Theoretically, the person who gained 13.3kg had minimal change in energy expenditure while the person who gained 4.3kg had a considerable increase in energy expenditure. 
Empty plate with knife and fork

How Calorie Intake Affects RMR 

  • Changes in body size will change RMR – larger bodies require more calories even at rest.
    • Therefore, an increase in caloric intake that results in weight gain will increase RMR.
  • RMR is also directly affected by your calorie intake via the process of metabolic adaptation.
    • When you increase your caloric intake, your RMR will increase slightly and if you decrease your caloric intake your RMR will decrease slightly.
    • Some examples of your body downregulating functions to conserve energy in a calorie deficit are; 
    • Decreased heart rate.
      • Downregulation of functions such as digestion and immunity. 
      • Fewer calories being used in the process of muscle growth. 
      • Loss of a regular menstrual cycle in more severe cases.

How Calorie Intake Affects TEF 

  • TEF usually makes up ~10% of calorie intake.
    • If you 3000kcal, we’d expect around 300kcal in energy expenditure from TEF. Dropping to 2000kcal could drop it down to 200kcal. 
  • This is higher if you consume more fibre, protein and unprocessed foods and lower if you do the opposite. 

How Calorie Intake Affects NEAT 

1. Bodyweight

  • Your caloric intake will influence your body weight.
  • If all other variables remain equal, lower body weight will reduce calories burned through activities such as daily steps etc.
  • Alternatively, a higher body weight will result in an increase in calories burned through this type of movement.

2. Impact on Subconscious Movement

  • Increases in calories usually result in increases in incidental movements.
    • People often feel more energetic and want to do more movement when they are on higher calories. 
    • People also tend to fidget more when they are on higher calories.
  • For example, bodybuilders who are prepping for a competition tend to move significantly less.
  • Increased subconscious movement is also seen in those with Parkinson’s due to unintended shaking. As a result, these individuals tend to have increased calorie requirements.

How Calorie Intake Affects EAT 

  • Reductions in body weight will lead to fewer calories burned through exercise (if all other factors remained equal).
    • Although this falls apart if exercise changes due to weight changes.
  • There is an argument that exercise becomes “more efficient” when on lower calories – but I wouldn’t focus on this too much. If that’s true, it’s likely a smaller factor than all the other variables.  
Man looking at plans and thinking

How Relevant Is All This? 

  • There are so many ways in which our calorie intake can either directly or indirectly impact our calorie expenditure.
  • It affects us whether we notice it or not. 
  • Some people experience these changes more than others.  
  • These changes in response to calorie intake can vary in how long they take to show up.
    • Effects on incidental and subconscious movement may happen fairly quickly after reducing or increasing calorie intake.
    • Alternatively, metabolic adaption can slowly occur over weeks and months.
    • This may also help explain reverse dieting.
      • This is the concept of slowly adding calories back in after a dieting phase (or vice versa).
      • By the time you start noticing weight gain, you may have already been in surplus for a few weeks.
      • Also highlights that the idea of ‘building up your metabolism before a fat loss phase’, may only work for a short period as these compensatory mechanisms will soon take effect.

Relevant Links / Resources

Blog Posts

Studies Mentioned