Effects of Prolonged Dieting

What happens when you have been on a diet for too long? Do diets stop working?

Metabolic damage does not exist. However, metabolic adaptation does exist after a prolonged energy deficit.  This is the process of adaptation your body goes through when dieting, this is why after so long the diet stops working!

Metabolic Adaptation, what does it do?


Hormones – Leptin

  • Released From Adipose Tissue
  • Regulates Hunger (Reduces)
  • Prolonged Dieting Lowers Leptin
  • Long-Term
  • Leptin Falls Not Only with Long-Term Reductions in Body Weight (and Body Fat) but also in Response to Short-Term Decrease in Energy Intake

Hormones – Ghrelin

  • Regulates Hunger (Increases)
  • Meal to Meal
  • Ghrelin Increased with Caloric Restriction


  • Energy Cost of Sitting, Fidgeting, Maintaining Posture, Muscle Tone and Leisure Activities
  • Decreases with Energy Restriction (due to Decreased Physical Activity, Improved Efficiency or both)
  • NEAT is Affected by Metabolic Adaptation
  • NEAT Reduces During Periods of Prolonged Dieting
  • This Reduces Overall Calorie Expenditure

How does this effect Fat Loss?

  • Caloric Restriction (CR) for 3 & 6 Months
  • Instructed to Maintain Activity Levels
  • Significant Reduction in TDEE (Total Daily Energy Expenditure) After 3 & 6 Months
  • M3 -431±51 Kcal/D
  • M6 -240±83 Kcal/D
  • Energy Expenditure was related to Decreased Physical Activity Despite Being Instructed to Maintain Activity Levels

Results of the Study Suggest;

  • Reduction in NEAT is Often Subconscious
  • Refeeds can be an effective way of overcoming these adaptations to dieting
  • A one day refeed is insufficient time to minimise these effects
  • Refeeds should be 2-3 days long with a high % of the additional calories coming from carbohydrates

What about Diet Fatigue?

Can Occur Due to:

  • Reduced Adherence
  • Food Boredom
  • Increased Mindless Eating
  • Reduced Accuracy in Portion Sizes


  • All Successful Diets are Due to a Caloric Deficit & Not The Diet Per Se
  • Diets Should be Used as a Tool for Weight Loss
  • Different Diets Suit Different People
  • Metabolic Adaptation is a Consequence of prolonged Dieting but Metabolic Damage Does NOT Exist