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Exploring the mystery of intermittent fasting and headaches

Magdalena Marvell, our resident nutritionist, looks at the potential health benefits of this popular dietary regime.

Magdalena Marvell is a Nutritional Practitioner and Founder of the Persea Clinic which helps support clients who want to optimise their health in areas such as gut health, hormonal balance, skin conditions, weight management, family nutrition. To find out more about her work please visit
Intermittent fasting, a popular dietary regimen, has garnered attention for its potential health benefits. Yet, for some individuals, navigating this fasting protocol may come with an unexpected challenge: headaches. Recent research from a 2023 study suggests that approximately 61% of intermittent fasters experience headaches during their fasting periods.
Understanding the science behind the pain
These headaches, categorised as secondary headaches, can often be attributed to disruptions in homeostasis – the body’s internal balance that regulates various functions in the body. 
Typically, fasting-induced headaches manifest as frontal discomfort or diffuse pain, often of mild to moderate intensity and non-pulsating nature. 
Moreover, individuals who frequently experience headaches are more prone to experiencing them during fasting compared to those who do not typically suffer from headaches.
Additionally, individuals may experience accompanying sensations of dizziness and weakness.
Several factors contribute to these headaches:
• Hypoglycaemia: Fasting can lead to low blood sugar levels, resulting in headaches for some individuals.
• Caffeine Withdrawal: Reduced or eliminated caffeine consumption during fasting may trigger withdrawal symptoms, including headaches.
• Dehydration: Insufficient fluid intake during fasting can lead to dehydration, a common headache trigger.
• Stress and Anxiety: Fasting-induced cortisol spikes may exacerbate stress levels, potentially leading to headaches.
For those embarking on intermittent fasting, adopting proactive measures can mitigate the likelihood of experiencing headaches:
• Gradual Transition: Start with shorter fasting durations and gradually increase them to allow the body to adapt gradually.
• Hydration: Ensure adequate fluid intake with water, herbal teas, or electrolyte supplements.
• Blood Sugar Monitoring: Watch for hypoglycaemic symptoms and address them promptly with small snacks or liquids such as bone broth.
• Stress Management: Incorporate stress-reduction techniques such as meditation or yoga to maintain emotional balance during fasting.
• Caffeine Moderation: Gradually reduce caffeine intake to minimise withdrawal symptoms.
Consulting a healthcare professional is recommended for severe or persistent headaches during fasting to rule out underlying health concerns.
Beyond headaches, intermittent fasting may entail other side effects:
• Cravings: Short-term food deprivation may intensify hunger and cravings for certain foods1.
• Digestive Changes: Some individuals may experience digestive discomfort or exacerbation of pre-existing conditions2.
• Irritability and Fatigue: Short-term fasting may lead to mood fluctuations and fatigue. In a study conducted in 2016 with 52 women, researchers discovered that participants exhibited significantly higher levels of irritability during an 18-hour fasting period compared to a non-fasting period3.
• Bad Breath: Fasting can cause halitosis; maintaining oral hygiene helps alleviate this issue. The underlying cause is a reduction in salivary flow combined with an increase in acetone levels in exhaled breath. When fasting, your body shifts to burning fat for energy, resulting in heightened acetone production in both your bloodstream and breath. Furthermore, dehydration, a common occurrence during intermittent fasting, can lead to dry mouth, exacerbating the potential for unpleasant breath odour4. Dental probiotic supplements could aid in combatting persistent bad breath. These supplements are accessible in various forms such as chewable tablets, probiotic drinks, and certain types of toothpaste even incorporate oral probiotics.
• Sleep Disruption: While inconclusive, some individuals may experience sleep disturbances during fasting. The rise in noradrenaline and cortisol levels can disrupt sleep patterns. Practicing good sleep hygiene and incorporating magnesium supplements can be beneficial in addressing this issue5.
• Malnutrition: Prolonged and unbalanced fasting may result in nutrient deficiencies. Improper intermittent fasting can result in malnutrition. Extended fasting periods without adequate nutrient replenishment, as well as mismanagement of calorie-restricted diets, can lead to malnourishment and other health issues. While many intermittent fasting methods allow for meeting calorie and nutrient needs, prolonged or extreme calorie restriction without careful planning can pose risks6.
While intermittent fasting might be suitable for some, it’s essential to understand that it may not be suitable or safe for everyone.
Certain individuals may be at a higher risk of experiencing adverse effects if they participate in intermittent fasting.
Healthcare professionals typically recommend that the following groups refrain from intermittent fasting:
• Expectant or breastfeeding mothers
• Children and adolescents
• Elderly individuals experiencing weakness
• Those with compromised immune systems
• Individuals with a history of eating disorders
• People diagnosed with dementia
• Individuals with a history of traumatic brain injury or post-concussive syndrome
It’s important to recognise that this list may not encompass all circumstances. For instance, healthcare practitioners have occasionally employed fasting as a therapeutic approach for managing epilepsy in children.
Intermittent fasting offers promising health benefits but can trigger headaches and other side effects. Prioritising hydration, blood sugar management, and stress reduction can enhance fasting comfort. Customising fasting routines and seeking medical guidance ensure a safe and effective fasting experience, especially for individuals with pre-existing health conditions. Remember, intermittent fasting isn’t one-size-fits-all – listen to your body and adjust accordingly to optimise your fasting journey.


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