What Are 0 Calorie Foods for Fasting? Fact vs. Fiction

October 5, 2025 •

5 min read

While the idea of "zero-calorie foods" for fasting is popular, the scientific fact is that, besides water, no food is truly calorie-free. This article clarifies what you can consume during a fast without breaking it and explores high-volume, low-calorie options for specific fasting methods.

Quick Summary

Explores the myth of zero-calorie foods and identifies genuinely minimal-calorie and non-caloric beverages permissible during a fast. It differentiates between clean and dirty fasting methods and discusses low-calorie options that support weight management.

Key Points

The Myth of 'Zero-Calorie' Foods: With the exception of water, no food is truly zero-calorie; most are simply very low in calories due to high water and fiber content.
Permissible Clean Fast Beverages: For a strict clean fast, plain water, unsweetened black coffee, and unsweetened tea are the only truly non-caloric options that won't break your fast.
Low-Calorie Options for 'Dirty Fasting': For less strict methods, low-calorie vegetables like celery, cucumber, and leafy greens can be consumed in moderation without a significant impact on your fasting state.
Understanding Fasting Protocols: The primary difference between clean and dirty fasting lies in the allowance of a small number of calories during the fasting window.
Focus on Hydration: Staying well-hydrated with water and other non-caloric beverages is the most effective way to manage hunger and maintain well-being during a fast.
Consult a Professional: Always seek advice from a healthcare provider before starting a fasting regimen, especially if you have existing health concerns.

The Myth of Truly Zero-Calorie Foods

The concept of "negative calorie foods"—where the body burns more energy digesting the food than the food contains—is a persistent myth. Scientific evidence does not support this claim. While certain foods, like celery and cucumber, are incredibly low in calories due to their high water and fiber content, your body still gains a small net amount of energy from them. The term "0 calorie foods" is a misnomer, and it's more accurate to think of them as ultra-low-calorie items. Understanding this distinction is crucial for anyone practicing intermittent fasting, especially those following a strict "clean fast" protocol where any caloric intake is prohibited.

Beverages That Won't Break a 'Clean' Fast

For a clean fast, the goal is to consume nothing that triggers an insulin response, as this would technically "break" the fasting state. Thankfully, several beverages fit this criterion and can help with hydration and curbing cravings.

Essential Fasting Beverages

Water: Plain water is the only truly zero-calorie and zero-macro beverage, making it the top choice for any fasting regimen. Staying hydrated is critical during a fast. You can opt for still or sparkling water.
Black Coffee: Unsweetened black coffee is widely accepted during a fast. It contains a negligible amount of calories and can help suppress appetite, while the caffeine provides an energy boost. Avoid adding milk, cream, or sugar.
Unsweetened Tea: Green tea, herbal tea (like chamomile or peppermint), and black tea are safe options as long as they are unsweetened. These can offer hydration and flavor variety without impacting your fast.
Diluted Apple Cider Vinegar (ACV): Some people mix a small amount of ACV with water, which may help with hydration and appetite control. A tablespoon of apple cider vinegar has a minimal calorie count, often considered negligible in most fasting circles.

Navigating 'Dirty Fasting' and Low-Calorie Options

Some fasting methods, often called "dirty fasting," allow for a minimal intake of calories (e.g., up to 50 calories) during the fasting window. This approach is less strict and can be more sustainable for some individuals. For this method, very low-calorie foods and beverages are considered acceptable.

Low-Calorie Vegetables for Fasting Days

These options are high in water and fiber, helping you feel full with very few calories.

Celery: A classic low-calorie snack, a medium stalk contains only about 5.6 calories.
Cucumber: Made of over 95% water, cucumbers are extremely low-calorie and very hydrating.
Lettuce: Iceberg or green leaf lettuce provides volume and crunch with minimal caloric impact.
Radishes: These peppery root vegetables offer flavor and crunch for a low-calorie snack.
Spinach: This leafy green is nutrient-dense and very low in calories, making it a great addition to salads during an eating window or a very small portion for dirty fasting.
Mushrooms: White mushrooms have an earthy flavor and only around 21 calories per cup.

Low-Calorie Fruits for Fasting Days

For those on a dirty fast, small portions of certain fruits can satisfy a sweet craving.

Watermelon: Extremely high in water, watermelon is a refreshing and hydrating choice.
Berries: Strawberries and mixed berries are packed with antioxidants and fiber for their low calorie count.
Grapefruit: This fruit has a tart flavor and a good dose of vitamin C with a relatively low-calorie density.

Clean vs. Dirty Fasting: A Comparison

Understanding the differences between these two fasting styles is key to choosing the right approach for your goals. The table below summarizes the core differences.


Feature	Clean Fasting	Dirty Fasting
Caloric Intake	Absolutely zero calories are consumed during the fasting window.	A small, controlled number of calories (e.g., <50) is consumed during the fast.
Permitted Items	Water, black coffee, unsweetened tea, diluted apple cider vinegar.	Allows for the same as clean fasting, plus very low-calorie foods and some artificial sweeteners.
Purpose	Maximizes metabolic state changes, such as autophagy and ketosis.	A more flexible and potentially sustainable option for those who struggle with strict zero-calorie fasting.
Effectiveness for Weight Loss	Highly effective by forcing the body to burn stored fat for energy.	Can still be effective for weight loss, as total calorie intake is significantly reduced.
Risks/Considerations	Can be challenging due to hunger; requires strict discipline.	Risk of spiking insulin, which could slightly reduce some fasting benefits; less clear physiological outcomes.

How to Stay Satisfied While Fasting

Whether you practice a clean or dirty fast, managing hunger is often the biggest hurdle. Incorporating these strategies can help you stay on track:

Hydration is Key: Drinking plenty of water and other allowed beverages helps you feel full. Often, thirst is mistaken for hunger.
Electrolytes: Bone broth is a popular and nutrient-rich option for replenishing electrolytes, especially during longer fasts.
Volume Eating (on dirty fast): Choosing high-volume, low-calorie foods like watery vegetables can fill up your stomach with minimal caloric intake, providing a sense of satiety.
Timing: For intermittent fasting, many people find it helpful to drink coffee or tea near the end of their fasting window to suppress appetite until their eating period begins.

Potential Risks and Considerations

While consuming low-calorie foods can aid in fasting, it's crucial to approach it with caution. Relying solely on low-calorie items can lead to nutrient deficiencies if not paired with a balanced diet during your eating windows. The ultimate goal is to maintain overall nutritional health. Crash dieting by only eating extremely low-calorie foods can be detrimental in the long run. Always consult a healthcare provider or a registered dietitian before beginning any new diet or fasting protocol, especially if you have pre-existing health conditions. The potential effects of artificial sweeteners on insulin response during a fast are not fully understood, so unsweetened, natural options are generally safest.

Juniper offers further resources and information on incorporating nutrient-rich, low-calorie foods into a balanced diet to support weight loss goals.

Conclusion

Ultimately, while the term "0 calorie foods for fasting" is largely a myth, several ultra-low-calorie vegetables and non-caloric beverages can support different fasting methods. For a strict clean fast, water, black coffee, and unsweetened tea are your best bets. For a more flexible dirty fast, small portions of high-water, high-fiber vegetables can help curb hunger without significantly impacting your fast. Prioritizing hydration and overall nutritional balance during your eating windows is essential for a safe and effective fasting regimen.

Frequently Asked Questions

No, unsweetened black coffee contains a negligible amount of calories and is widely considered acceptable during a fast. However, adding sugar, milk, or cream will break the fast.

Depending on the fasting protocol, some people on a "dirty fast" consume diet soda with zero-calorie sweeteners. However, since the impact of artificial sweeteners on insulin response is not fully understood, it's safest to stick to water, black coffee, or tea for a strict clean fast.

High-water, high-fiber vegetables like watercress, lettuce, and cucumber are among the lowest-calorie food options, often containing less than 10 calories per serving.

No, celery is not truly zero-calorie, but it is extremely low in calories, with a high water content. It's often referred to as a "negative calorie food," though this is a myth, as you still gain a small net caloric intake from it.

Bone broth contains calories and can break a strict clean fast, but it may be allowed during a dirty fast or a modified fasting protocol. Some people use it during longer fasts to replenish electrolytes.

Many low-calorie vegetables and fruits, like leafy greens, are packed with essential vitamins, minerals, and fiber, making them nutritious additions to your diet, especially during your eating window.

No, relying solely on ultra-low-calorie foods is not sustainable or healthy, as it can lead to nutrient deficiencies and unsatisfied hunger. These foods should be part of a balanced diet, not the only focus.