What are the side effects of egg fasting?

November 30, 2025 •

4 min read

According to nutrition experts, a restrictive diet like the egg fast is not recommended for long-term health and is often linked to unpleasant side effects. This guide breaks down what are the side effects of egg fasting, from short-term issues like 'keto flu' to longer-term nutritional deficiencies.

Quick Summary

This article explores the common side effects associated with the short-term egg fast, including 'keto flu' symptoms, digestive problems, and the risk of nutritional gaps. It also addresses potential long-term health concerns and who should avoid this highly restrictive diet.

Key Points

Keto Flu Symptoms: Initial adaptation to the egg fast can cause headaches, fatigue, and nausea as your body adjusts to burning fat for energy.
Nutritional Deficiencies: The diet's lack of variety can lead to deficiencies in essential vitamins and minerals like fiber, vitamin C, and potassium.
Digestive Issues: The severe lack of dietary fiber often results in constipation, though some may experience diarrhea.
High Risk for Some Individuals: People with certain medical conditions, such as kidney disease, liver issues, or a history of eating disorders, should avoid the egg fast.
Unsustainable and Rebound Weight Gain: As a short-term solution, the egg fast is not sustainable and often leads to rebound weight gain after it is over.
Negative Impact on Gut Health: Restricting fiber from whole grains and vegetables can negatively affect the gut microbiome.
Consult a Healthcare Professional: It is highly recommended to consult a doctor before starting any restrictive diet like the egg fast, especially with pre-existing health concerns.

Understanding the Egg Fast: A Short-Term Ketogenic Approach

An egg fast is a highly restrictive, short-term diet, typically lasting three to five days, designed to help break through a weight-loss plateau in a ketogenic diet. The plan involves consuming mainly eggs, cheese, and healthy fats. By severely limiting carbohydrates, the body is forced into a state of ketosis, where it burns fat for energy instead of glucose. While some individuals seek the rapid results promised by this method, it is not scientifically studied and carries a number of significant side effects and health risks. The strict and monotonous nature of the diet is often difficult to sustain, and many of the associated side effects are related to the body's reaction to carbohydrate restriction and a lack of nutritional diversity.

The 'Keto Flu' and Other Short-Term Discomforts

One of the most immediate side effects of an egg fast, particularly for those new to a ketogenic diet, is a cluster of symptoms often referred to as the 'keto flu'. This occurs as the body transitions from relying on carbs to using fat for fuel, a process called fat adaptation.

Fatigue and Tiredness: A lack of carbohydrates, the body's primary energy source, can lead to a significant drop in energy levels, causing tiredness and lethargy.
Headaches and Brain Fog: The withdrawal from carbohydrates and the metabolic shift can cause severe headaches, mental fogginess, and difficulty concentrating.
Nausea and Upset Stomach: The sudden change in diet can upset the digestive system, leading to feelings of nausea and general stomach upset.
Dizziness: Electrolyte imbalances, particularly a drop in sodium, can cause lightheadedness or dizziness during the initial stages of the fast.
Irritability and Mood Changes: The strict nature of the diet and fluctuations in energy can negatively impact mood, leading to irritability.
Sleep Disturbances: Some individuals report having trouble sleeping or experiencing changes in their sleep patterns while on the fast.

The Impact on Digestive Health

The egg fast's extremely low fiber content is a major drawback that directly affects digestive health. Fiber is crucial for maintaining a healthy gut microbiome and ensuring regular bowel movements. Without it, the digestive system can become sluggish.

Common Digestive Issues:

Constipation: The most frequently reported digestive issue is constipation, caused by the severe lack of dietary fiber.
Diarrhea: For some, the high fat and low fiber content can have the opposite effect, leading to diarrhea.
Bloating: A stomach upset or reaction to the high volume of eggs can cause bloating and discomfort.

Risks of Nutritional Deficiencies

While eggs are a nutrient-dense food, an egg-only diet is far from a nutritionally complete one. The limited food intake means many essential vitamins and minerals are missing, which poses a serious health risk if the diet is followed for an extended period.

Potential Deficiencies:

Fiber: Complete lack of fiber from fruits, vegetables, and grains.
Vitamins: Insufficient intake of Vitamin C, folate, and certain B vitamins.
Minerals: Low levels of magnesium, potassium, copper, and molybdenum.
Antioxidants: Lack of a variety of fruits and vegetables means missing out on beneficial antioxidants.

Long-Term Health Concerns and Weight Regain

Beyond the short-term issues, an egg fast is an unsustainable diet pattern that can lead to long-term problems. Fad diets like this can lead to yo-yo dieting, where rapid weight loss is followed by even quicker weight regain.


Comparison of Egg Fast vs. Balanced Keto Diet	Feature	Egg Fast	Balanced Ketogenic Diet
Food Variety	Highly restrictive; primarily eggs, cheese, fat.	Allows a wider variety of low-carb vegetables, meats, fish, and nuts.
Fiber Content	Extremely low to none.	Can be managed with fibrous low-carb vegetables and seeds.
Nutritional Balance	High risk of vitamin and mineral deficiencies.	Better balanced with careful planning to include all essential nutrients.
Sustainability	Not intended for long-term use; adherence is challenging.	Sustainable as a long-term lifestyle with proper planning.
Weight Regain Risk	High risk of rebound weight gain due to unsustainability.	Lower risk of weight regain when transitioned to a maintenance plan.

Who Should Avoid an Egg Fast?

The highly restrictive nature of an egg fast makes it unsuitable and potentially dangerous for several groups of people. Individuals with pre-existing medical conditions should never attempt this diet without medical supervision.

Groups at High Risk:

Kidney, liver, or gallbladder issues: The high fat and protein load can exacerbate pre-existing conditions affecting these organs.
High cholesterol: Though research is mixed on eggs and cholesterol, individuals with familial hypercholesterolemia should exercise caution and consult a doctor.
Diabetes: The diet is not suitable for people with diabetes.
Eating disorders: The restrictive approach can be a trigger for those with a history of eating disorders.
Pregnant or breastfeeding women: Nutrient needs are much higher during these periods, and the diet is nutritionally incomplete.
Individuals with an egg allergy or intolerance: Obvious and severe reactions are possible.

Conclusion: A Risky Approach to Short-Term Goals

While the appeal of quick weight loss can be strong, the side effects of egg fasting, from the uncomfortable 'keto flu' to significant nutritional deficiencies, make it a risky and unsustainable strategy. The diet's short duration and lack of nutritional balance mean that any weight loss achieved is likely to be water weight or temporary, often leading to rapid weight regain. For safe and lasting results, health professionals recommend a balanced and varied approach to diet and exercise. If you are considering the egg fast, it is crucial to consult with a doctor or registered dietitian beforehand to assess the potential risks for your specific health profile. A more moderate, evidence-based approach is almost always the healthier and more effective path to achieving your health goals.

Frequently Asked Questions

The 'keto flu' is a term for a collection of symptoms, including headaches, fatigue, and irritability, that can occur as your body transitions from burning carbohydrates to fat for energy.

Yes, an egg fast often causes constipation due to the severe lack of dietary fiber, which is crucial for healthy bowel movements and is not present in eggs.

No, the egg fast is not nutritionally complete. While eggs provide many nutrients, the diet is highly restrictive and lacks sufficient fiber, vitamin C, and several important minerals.

Individuals with pre-existing conditions like kidney, liver, or gallbladder disease, as well as pregnant or breastfeeding women, people with diabetes, or those with a history of eating disorders should not attempt an egg fast.

There is a high risk of regaining the weight lost during an egg fast. The diet is not a long-term solution and often leads to rebound weight gain once normal eating habits resume.

While the link between dietary and blood cholesterol is complex, individuals with a predisposition to high cholesterol or heart issues should be cautious, as eggs are high in cholesterol.

An egg fast is typically only recommended for a very short duration, usually three to five days. It is not advised to follow it for longer than this due to the risk of nutrient deficiencies.