Is it unhealthy to go 24 hours without food? The benefits, risks, and expert consensus

November 1, 2025 •

3 min read

According to extensive research, the human body is physiologically capable of withstanding periods without food, a trait inherited from our hunter-gatherer ancestors. However, whether it is unhealthy to go 24 hours without food depends heavily on an individual's health, preparation, and refeeding strategy. This practice, a form of intermittent fasting, triggers metabolic changes but requires careful consideration to ensure safety and effectiveness.

Quick Summary

A 24-hour fast is a popular intermittent fasting method with potential benefits like weight loss and improved metabolic health, but it also carries risks. The body shifts from burning glucose to fat for energy, a process known as ketosis, which can enhance cellular repair. However, careful preparation, hydration, and a mindful refeeding process are essential to minimize side effects and ensure safety. This practice is not recommended for everyone, particularly those with underlying health conditions or a history of disordered eating.

Key Points

Generally Safe for Healthy Adults: An occasional 24-hour fast is typically safe for healthy individuals and can lead to weight loss and metabolic improvements.
Not for Everyone: People with diabetes, pregnant or breastfeeding women, and those with a history of eating disorders should avoid 24-hour fasting unless under medical supervision.
Metabolic Shift: During a 24-hour fast, the body transitions from using glucose for energy to burning stored fat and producing ketones.
Cellular Repair: Fasting can trigger autophagy, a process where cells cleanse and repair themselves, potentially supporting longevity.
Stay Hydrated: It is critical to drink plenty of calorie-free liquids, such as water and herbal teas, throughout the 24-hour period to prevent dehydration.
Break the Fast Gently: The reintroduction of food should be gradual, starting with small, easily digestible meals to avoid overwhelming the digestive system.

The Physiological Journey: What Happens During a 24-Hour Fast?

A 24-hour fast, or "eat-stop-eat" method, leads to metabolic changes as the body adapts to a lack of food.

Metabolic Stages During a 24-Hour Fast

During the first 0–4 hours after eating (the fed state), the body uses glucose for energy and stores excess as glycogen. From 4–16 hours (early fasting), insulin levels drop, and the body starts using stored glycogen. Hunger may increase during this time. Between 16–24 hours, glycogen stores deplete, and the body enters ketosis, burning stored fat for energy and producing ketones. Approaching the 24-hour mark, cellular repair processes like autophagy may increase, along with potential increases in growth hormone.

Potential Benefits and Significant Risks

Engaging in a 24-hour fast can offer several health benefits, but it also comes with notable risks.

Potential Benefits of a 24-Hour Fast

Benefits may include weight loss by reducing calorie intake and promoting fat burning. It can also improve metabolic health by enhancing insulin sensitivity and blood sugar regulation, potentially lowering the risk of type 2 diabetes and improving cardiovascular health by affecting blood lipid profiles. Additionally, fasting is thought to stimulate autophagy, a cellular repair process.

Significant Risks and Side Effects

Key risks and side effects include dehydration if insufficient calorie-free fluids are consumed. Common discomforts like hunger, fatigue, and irritability are also possible. Fasting can be particularly risky for individuals with diabetes due to the potential for hypoglycemia. It's also not advised for those with a history of eating disorders, as it can exacerbate unhealthy patterns. Breaking a fast improperly by overeating can cause digestive issues.

Comparison of 24-Hour Fasting vs. Other Methods


Feature	24-Hour Fast (Eat-Stop-Eat)	16:8 Fast (Time-Restricted Eating)	5:2 Fast (Modified Fasting)
Fasting Frequency	1–2 times per week	Every day	2 days per week
Caloric Intake	Zero calories for 24 hours	Eat within an 8-hour window	500–600 calories on fasting days
Intensity	High; can cause fatigue and irritability initially	Moderate; most fasting occurs during sleep	Moderate; still involves some caloric intake
Adaptability	Can be difficult to sustain long-term for some people	Easier for beginners and highly sustainable	Can be easier than a complete 24-hour fast
Ketosis Level	Promotes deeper ketosis than 16:8	Mild ketosis; benefits depend on food choices	Moderate ketosis on fasting days

Practical Steps for a Safe 24-Hour Fast

Following practical steps is essential for a safe and effective 24-hour fast.

Prepare: Eat a balanced meal before fasting with protein, fiber, and healthy fats to prolong satiety.
Hydrate: Drink plenty of calorie-free fluids throughout the fast to prevent dehydration.
Stay Busy: Engage in activities to help manage hunger and focus during the fasting period.
Listen to Your Body: If you experience severe symptoms like dizziness or weakness, break the fast and seek medical advice.
Break Gently: Consume a small, easily digestible meal first, avoiding heavy or processed foods to prevent digestive issues. Examples include bone broth or cooked vegetables.

Is it unhealthy to go 24 hours without food? Conclusion

For healthy individuals, occasional 24-hour fasting is generally safe and may offer benefits like weight loss and improved metabolic health. However, it is not suitable for everyone, particularly those pregnant or breastfeeding, children, those with eating disorders, or certain medical conditions like diabetes. Safe fasting requires proper preparation, adequate hydration, and a careful approach to reintroducing food. Consulting a healthcare professional before starting any fasting regimen is recommended to ensure it aligns with your health needs. A balanced lifestyle combining healthy eating and exercise is often the most sustainable path to well-being.

Authoritative Link

For more information on the stages of fasting and metabolic changes, visit the National Institutes of Health.

Frequently Asked Questions

Common side effects include hunger pangs, fatigue, irritability, and headaches, especially for those new to fasting. These symptoms often subside as the body adapts over time.

Yes, you can consume calorie-free beverages such as plain water, black coffee, and unsweetened herbal tea. It is vital to stay hydrated, as your body gets less water from food.

Research suggests that intermittent fasting can be as effective for weight loss as standard calorie restriction, but it is not necessarily superior. Its success often depends on individual adherence and avoiding overeating during feeding windows.

It's best to break your fast with a small, light, and easily digestible meal. Options like bone broth, a handful of nuts, or cooked vegetables are good choices before gradually reintroducing more substantial foods.

Certain individuals, including pregnant or breastfeeding women, children and adolescents, those with diabetes, and people with a history of eating disorders, should avoid fasting.

For healthy individuals, a 24-hour fast is not long enough to trigger 'starvation mode'. This state, characterized by a significant metabolic slowdown, typically occurs only after several consecutive days or weeks without food.

Most experts suggest practicing a 24-hour fast no more than once or twice a week to ensure safety and allow for adequate nutrient intake. It is not a sustainable long-term solution for daily calorie restriction.