Fasting Isn’t for Everyone: When Intermittent Fasting Can Do More Harm Than Good

By Dr D Michael Elliott MSc D.C. CFMP Lifestyle Medicine Practitioner & Chiropractor

The Fasting Phenomenon

Intermittent fasting (IF) has become one of the most talked-about health trends of the decade.   It’s praised for its potential to improve metabolic health, reduce inflammation, support weight balance, and promote cellular repair through autophagy.

But while fasting has its place, it’s not a one-size-fits-all solution. What’s missing from most conversations is the context — our genetic individuality, hormonal state, stress resilience, and nutritional history all determine whether fasting heals or harms.

 When Fasting Becomes a Stressor, Not a Healer

For some, fasting is a gentle metabolic reset. For others, it can create energy and hormone imbalances that stress the body rather than strengthen it.

• Cortisol & Adrenal Stress: Prolonged fasting triggers cortisol release to maintain blood sugar. In genetically stress-sensitive individuals or those already dealing with adrenal fatigue, this can worsen anxiety, disrupt sleep, and flatten energy.

• Thyroid Down-Regulation: People with variations in thyroid-related genes (like DIO2 or MCT8) may have difficulty maintaining active thyroid hormone (T3) levels when fasting too long, leading to fatigue, weight gain, and cold intolerance.

• Poor Detox or Methylation Genes: Those with sluggish COMT, MTHFR, or GST pathways may accumulate more oxidative stress during prolonged fasting due to reduced capacity for antioxidant and estrogen metabolism.

• Female Hormone Sensitivity: Women with lower leptin or estrogen levels, or with polymorphisms in estrogen or progesterone receptors, can experience menstrual irregularities or mood changes when fasting excessively.

What starts as a metabolic experiment can become a hormonal stress test if not matched to individual biochemistry.

Cultural Wisdom: More Than One Path to Longevity

While fasting practices appear in some long-lived cultures, it’s important to recognize that longevity has never relied on one universal eating pattern.

In many traditional societies — from rural Mediterranean communities to Japanese and Scandinavian populations — people thrived on three balanced meals a day, often with a morning or afternoon tea. Their diets emphasized:

• Whole, minimally processed foods

• Abundant vegetables and fibre

• Moderate natural fats and proteins

• Communal eating, sunlight exposure, and daily movement

These populations have enjoyed comparable life expectancy to cultures that practiced periodic fasting, proving that how and what we eat matters as much as when we eat.

The Genetic Layer: Personalized Nutrition Matters

Modern nutritional genomics has revealed why some people thrive on fasting and others struggle. Variants in genes governing:

• Insulin sensitivity (IRS1, PPARγ)

• Caffeine metabolism (CYP1A2)

• Stress response (NR3C1, COMT)

• Methylation and detox (MTHFR, COMT, GSTT1)

  
  

  influence how our bodies respond to long fasting intervals.

Fasting may optimize metabolism in some while elevating inflammation or impairing hormone balance in others.  This is why personalized nutrition testing — including genetic and hormonal profiling — should precede any strict fasting regimen.

Finding Your Balance

For many people, a more moderate rhythm — three balanced meals daily, occasional light fasting, and consistent nutrient-dense whole foods — provides the same benefits without the physiological strain .What truly matters is metabolic flexibility — the ability to move smoothly between fed and fasted states without triggering stress chemistry.

If fasting leaves you anxious, fatigued, or sleepless, it’s not working for you. Listening to your body is the most valuable biofeedback tool you have.

The Takeaway

Fasting can be a powerful metabolic tool — but only when applied thoughtfully and individually.  Genetics, stress physiology, and nutritional status all shape your response. Just as some cultures thrived on fasting, others flourished on regular meals — proof that health has many pathways.

Before committing to an intermittent fasting routine, consider functional testing and personalized guidance. The goal isn’t to follow the latest trend; it’s to find your body’s unique rhythm for energy, hormone balance, and longevity.