Can Fasting Cause Long-Term Issues? Unpacking the Risks

November 18, 2025 •

4 min read

According to The Emily Program, the long-term safety of intermittent fasting is largely unconfirmed due to limited human studies, with restrictive eating potentially heightening the risk of disordered eating in susceptible individuals. This raises important questions about whether fasting can cause long-term issues, and for whom the risks might outweigh the benefits.

Quick Summary

This article examines the potential long-term risks associated with various forms of fasting, including impacts on metabolic health, hormonal balance, mental well-being, and the heightened risk of developing disordered eating behaviors. It emphasizes that medical supervision is crucial for those with pre-existing conditions and for prolonged fasts.

Key Points

Disordered Eating Risk: Fasting can be a trigger or amplifier for disordered eating patterns, especially in susceptible individuals, by promoting a restrictive mindset.
Metabolic Adjustments: The body adapts during fasting, but long-term effects can include metabolic slowdown and weight cycling if not managed carefully.
Hormonal Impacts: Fasting may cause hormonal disruptions, particularly affecting the menstrual cycle in women.
Kidney and Heart Health: Risks include dehydration and electrolyte imbalances, which can strain kidneys, and emerging, though debated, concerns exist regarding long-term heart health.
Nutrient and Muscle Concerns: Prolonged fasting without a balanced re-feeding strategy risks malnutrition and can contribute to muscle loss.
Medical Supervision is Key: Certain populations, such as diabetics, pregnant women, and those with a history of eating disorders, should avoid fasting or only do so under strict medical guidance.

Understanding Potential Long-Term Risks

Fasting has been practiced for centuries, but its recent surge in popularity for weight management has brought increased scrutiny to its potential long-term consequences. While short-term fasts are generally considered safe for most healthy individuals, the effects of prolonged or repeated fasting over months or years are less understood due to a lack of robust, long-term human studies.

Disordered Eating and Psychological Effects

One of the most significant and concerning long-term risks of fasting is its potential to trigger or exacerbate disordered eating. Fasting promotes a restrictive mindset, and for some, overriding natural hunger cues can create an unhealthy and obsessive relationship with food. This can manifest as anxiety around eating, a rigid adherence to fasting schedules, and, for some, the development of a binge-restrict cycle. This risk is particularly high for individuals with a history of eating disorders or those genetically predisposed to them. Psychologically, the deprivation experienced during fasting can lead to increased stress, irritability, mood swings, and a fixation on food.

Metabolic and Endocrine System Impacts

Fasting fundamentally alters the body's metabolism, but its long-term effects on metabolic and endocrine systems are still under investigation. Some potential consequences include:

The 'Yo-Yo' Effect: For many, the weight lost during fasting can be quickly regained once normal eating resumes, especially if sustainable lifestyle changes are not adopted. This can be mentally frustrating and contribute to unhealthy dieting cycles.
Hormonal Imbalances: Fasting can impact hormone levels, especially in women. Anecdotal and some early research reports suggest that intermittent fasting may disrupt female reproductive hormones, leading to issues like irregular menstrual cycles or amenorrhea. For women who are pregnant, breastfeeding, or trying to conceive, fasting is typically not recommended.
Blood Sugar Dysregulation: While fasting can improve insulin sensitivity for some, it poses a risk for individuals with pre-existing blood sugar issues, such as diabetics. Hypoglycemia is a serious risk for those taking medications that affect blood sugar, and prolonged fasting requires medical supervision.

Organ Health: Kidneys and Heart

Kidney Health Concerns

Dehydration and Electrolyte Imbalance: Extended periods without food and water can easily lead to dehydration and a dangerous imbalance of essential electrolytes like sodium and potassium. This is especially risky for those with existing kidney problems, as it increases the workload on the kidneys and raises the risk of kidney stones. Proper hydration and electrolyte supplementation are critical for longer fasts.

Heart Health Uncertainties

Recent, non-peer-reviewed research presented at a conference suggested a potential doubling of cardiovascular death risk for people practicing intermittent fasting, particularly time-restricted eating. However, these findings had significant limitations, such as not accounting for diet quality or other lifestyle factors, and require further peer-reviewed investigation. Other studies point to potential benefits for heart health markers under proper supervision. This highlights the need for a cautious, personalized approach guided by a doctor, especially for individuals with underlying heart conditions.

Nutritional Deficiencies and Muscle Loss

Malnutrition: Without a properly planned, nutrient-dense diet during eating windows, individuals who fast regularly risk developing nutritional deficiencies. Vitamins, minerals, and other essential nutrients may be missed, leading to fatigue, weakness, and other health issues. Supplementation may be necessary, but whole foods are always preferred.
Muscle Loss: While the body prioritizes fat for fuel during fasting, there is still a risk of muscle loss, especially with prolonged or poorly executed fasts. Some studies suggest muscle function can be preserved, but relying solely on fat stores without adequate protein intake can be detrimental to body composition over the long term.

Fasting Protocols: Risks and Considerations


Feature	Intermittent Fasting (e.g., 16:8)	Prolonged Fasting (24+ hours)
Primary Risks	Less severe, but still includes potential for disordered eating, short-term side effects (headaches, mood swings), and hormonal impacts.	Higher risk of dehydration, electrolyte imbalances, nutrient deficiencies, and severe fatigue. Increased potential for serious complications like refeeding syndrome if not managed correctly.
Side Effects	Typically milder side effects that often diminish over time as the body adapts.	More intense side effects like extreme hunger, dizziness, and heightened fatigue are common.
Medical Supervision	Generally recommended for individuals with underlying health conditions or a history of eating disorders.	Strongly recommended or required for any fast lasting longer than 72 hours due to increased risk of complications.
Sustainability	Often considered more sustainable long-term due to shorter fasting windows.	Difficult to maintain regularly due to significant physiological stress and potential for side effects.

Populations Who Should Avoid or Be Cautious with Fasting

Fasting is not suitable for everyone. Certain individuals should avoid fasting or only do so under strict medical supervision:

People with a history of eating disorders.
Pregnant or breastfeeding women.
Children and teenagers who require sufficient calories for growth.
Individuals with diabetes or other blood sugar regulation issues.
Those who are underweight or have a history of amenorrhea.
Individuals with heart disease or low blood pressure.
Anyone taking prescription medications, as timing of doses may need adjustment.

Conclusion: The Importance of Personal Assessment

While fasting offers potential health benefits, it is crucial to recognize that its long-term effects are not yet fully understood and vary significantly between individuals. For some, the practice can pose serious risks, including the development of disordered eating, hormonal imbalances, and potential strain on vital organs like the kidneys and heart. Instead of viewing fasting as a guaranteed solution, it should be approached with caution and awareness of personal health status. A healthy lifestyle incorporating a balanced diet, adequate hydration, exercise, and sufficient sleep is paramount. Consult a healthcare professional before starting any fasting regimen to ensure it is appropriate for your individual needs and health history.

For more detailed information on practicing fasting safely, you can refer to resources like this guide from Healthline.

Frequently Asked Questions

Yes, research indicates that fasting can be a risk factor for developing or worsening disordered eating behaviors. The restrictive mindset and ignoring of natural hunger cues can lead to obsessive thoughts about food and a binge-restrict cycle in some individuals.

Long-term effects are not yet fully confirmed due to limited research, but potential risks include impacts on metabolic health, hormonal balance (especially in women), and a heightened risk for disordered eating. For most healthy people, short-term mild side effects typically lessen with adaptation.

While healthy kidneys are not typically harmed by careful, short-term fasting, prolonged fasting increases the risk of dehydration and electrolyte imbalances. This can be dangerous for individuals with pre-existing kidney conditions and may increase the risk of kidney stone formation.

Yes, some anecdotal and research findings suggest that fasting can disrupt female hormones, which may lead to menstrual cycle irregularities. This is particularly a concern for women who are underweight, athletes, or attempting to conceive.

Fasting generally spares muscle by prioritizing fat for energy, but prolonged or improperly managed fasts can contribute to muscle loss. To minimize this risk, consuming adequate protein during eating windows and incorporating resistance exercise is important.

Fasting should be avoided by pregnant or breastfeeding women, children, teenagers, individuals with a history of eating disorders, those with diabetes, and anyone underweight. It is also recommended to consult a doctor if you have a chronic illness or take prescription medication.

To mitigate risks, it is essential to stay well-hydrated, supplement with electrolytes during longer fasts, eat a nutrient-dense diet during eating periods, and listen to your body. Adopting a balanced lifestyle with regular exercise is also key.