Intermittent fasting (IF), a dietary pattern alternating between eating and voluntary fasting periods, has gained immense popularity for its purported benefits in weight loss and metabolic health. However, what is often overlooked in mainstream media is that this approach is not suitable for everyone. For certain individuals, IF can pose significant and even dangerous health risks. Consulting a healthcare provider is the first and most crucial step before attempting any form of fasting.
Individuals with a History of Eating Disorders
Experts universally caution against intermittent fasting for anyone with a history of or active eating disorder, such as anorexia nervosa or bulimia. Restrictive dieting is a major predictor for the development or relapse of disordered eating patterns. For these individuals, IF can trigger a cycle of restriction and binge eating, intensifying feelings of anxiety and shame around food. Recovery from an eating disorder emphasizes consistent eating patterns and listening to the body’s natural hunger and fullness cues—principles directly contradicted by IF. A health-promoting approach focuses on building a healthy relationship with food, which is undermined by fasting protocols.
People with Diabetes or Blood Sugar Issues
While some studies have shown IF can improve insulin sensitivity in people with prediabetes, the practice is particularly risky for individuals with existing diabetes, especially those on medications. The danger lies in significant blood sugar fluctuations:
- Hypoglycemia: People with type 1 diabetes on insulin, or those with type 2 diabetes taking insulin or other medications (like sulfonylureas), risk dangerously low blood sugar levels (hypoglycemia) during prolonged fasting periods. This can cause dizziness, confusion, or fainting.
- Hyperglycemia: Conversely, binge eating during the feeding window can cause high blood sugar (hyperglycemia), leading to poor long-term glucose control and an increased risk of diabetic complications. Medical supervision is essential, and many experts advise against fasting for individuals with poorly controlled or 'labile' diabetes.
Pregnant and Breastfeeding Women
Pregnancy and breastfeeding are periods of high nutritional and energy demands, and intermittent fasting is strongly discouraged. Fasting can lead to:
- Nutrient Deficiencies: Meeting the increased calorie and nutrient needs for a developing baby is difficult within a restricted eating window, which could increase the risk of deficiencies.
- Impact on Fetal Development: Animal studies have shown maternal IF during pregnancy can cause fetal growth restriction. Human studies on Ramadan fasting, while showing mixed results, suggest potential impacts that warrant caution.
- Compromised Milk Supply: For breastfeeding mothers, inadequate caloric intake can negatively impact milk supply and composition, affecting infant nutrition.
- Increased Stress Hormones: Fasting increases stress hormones like cortisol, which has been linked to a higher risk of premature birth.
Older Adults
While IF can offer metabolic benefits for some, older adults face a unique set of risks that make the practice inadvisable, especially without medical oversight.
- Muscle Mass Loss: Age-related muscle loss, known as sarcopenia, is a major concern. During weight loss, older adults can lose a higher percentage of lean mass, and IF, particularly without adequate protein and strength training, can exacerbate this.
- Dehydration Risk: Older adults are more susceptible to dehydration, and longer fasting periods increase this risk, potentially leading to low blood pressure or disorientation.
- Higher Risk of Falls: The combination of dehydration, muscle loss, and potential dizziness makes older individuals more prone to falls and injury.
Individuals on Specific Medications
Many medications must be taken with food to ensure proper absorption and to prevent stomach irritation or nausea. An IF schedule can interfere with this critical timing. Medications to be especially cautious with include:
- Diabetes medications that lower blood sugar.
- NSAIDs like ibuprofen, which can irritate the stomach lining.
- Blood pressure medications or diuretics, which can be affected by changes in hydration and electrolyte balance during fasting.
- Thyroid medications that may need specific timing relative to meals. Any changes to medication timing or dosage should only be made under the strict guidance of a doctor.
Potential Dangers: Refeeding Syndrome
Though rare with typical IF protocols, individuals who are underweight, malnourished, or have undergone prolonged caloric restriction are at risk for refeeding syndrome. This potentially fatal condition occurs when food is reintroduced too quickly, causing dangerous shifts in fluids and electrolytes. Symptoms include muscle weakness, seizures, and heart failure. It is why medically supervised refeeding is critical for those recovering from severe malnutrition.
Comparison: Who Should & Shouldn't Consider IF
| Feature | Consider IF | Caution/Avoid IF | Recommended Approach |
|---|---|---|---|
| Current Health | Generally healthy adult, normal or overweight BMI. | Pregnant, breastfeeding, underweight, history of eating disorders, certain chronic diseases (like diabetes). | Consult a doctor first; focus on a balanced diet if in the 'caution' group. |
| Medication Use | Takes medications unaffected by food, or has a flexible schedule. | Takes medications that must be taken with food (e.g., NSAIDs, some diabetes meds). | Do not adjust medication schedule without a doctor's guidance. |
| Age | Young to middle-aged adults. | Children, adolescents, older adults (especially >70). | Prioritize consistent nutrition for growth and muscle maintenance. |
| Risk of Disordered Eating | No history or risk factors for disordered eating. | History of or risk for disordered eating; highly restrictive mindset. | Focus on intuitive eating and a positive relationship with food. |
| Nutritional Needs | Can meet nutritional needs within an eating window. | High nutrient demands (pregnancy, breastfeeding) or risk of deficiencies. | Prioritize consistent and adequate nutrient intake over timing. |
When to Stop Intermittent Fasting
For those who do try IF under a doctor's supervision, certain symptoms signal that it's time to stop and seek medical advice.
- Persistent dizziness or extreme fatigue.
- Changes to menstrual cycle or fertility concerns.
- Increased anxiety, irritability, or mood swings.
- Significant muscle loss or weakness.
- Digestive issues like bloating, constipation, or acid reflux.
Conclusion
While intermittent fasting can be a useful tool for some, it is not a universally safe approach to diet and health. The potential risks for specific groups, including pregnant women, older adults, and those with diabetes or a history of eating disorders, are significant and should not be overlooked. Always prioritize safety over trend when it comes to your health. A conversation with a healthcare professional before starting any restrictive dietary regimen is the most responsible and vital step to ensure it aligns with your unique health profile. Focus on nourishing your body consistently rather than adhering to rigid eating schedules that may cause more harm than good.
Helpful Resource
For comprehensive information on a range of health topics, visit Johns Hopkins Medicine.
