What Can and Can't You Have While Fasting?

October 29, 2025 •

4 min read

According to a study cited by Johns Hopkins, intermittent fasting has been practiced for decades and is associated with various health benefits, including weight loss and improved metabolic function. To successfully leverage these advantages, it is critical to understand what can and can't you have while fasting, as consuming the wrong items can halt your progress and negate the fast's effects.

Quick Summary

This guide details the liquids and supplements permitted during a fast, identifies items that will break it, and offers strategies for maximizing health benefits during eating windows and refeeding periods.

Key Points

Zero-Calorie is Key: For a strict fast, only consume items with zero calories, such as plain water, black coffee, and unsweetened tea, to avoid breaking the fast.
Avoid Sugar and Processed Foods: During both fasting and eating windows, limit sugary drinks, refined carbs, and processed snacks that can spike insulin and negate fasting benefits.
Break Your Fast Gently: Reintroduce food with easily digestible, nutrient-dense options like bone broth or cooked vegetables, especially after longer fasts.
Stay Hydrated: Maintain proper hydration with water throughout your fasting period. Consider electrolytes for longer fasts to prevent side effects.
Fuel Your Eating Window Wisely: Focus on a balanced diet of lean proteins, healthy fats, and fiber-rich vegetables and fruits when it's time to eat.
Adjust for Your Fast Type: Recognize that acceptable intake varies by fasting method (e.g., intermittent fasting vs. water fasting). Never consume anything with calories during a water fast.

Navigating Different Fasting Approaches

Understanding which foods and drinks are allowed depends heavily on the specific type of fast you are undertaking. While the strictest definition of fasting means zero calories, methods like intermittent fasting (IF) offer more flexibility with certain non-caloric beverages.

Intermittent Fasting (IF)

This popular method involves alternating between periods of eating and fasting, most commonly the 16/8 approach, where you fast for 16 hours and eat within an 8-hour window. The primary goal is to lower insulin levels and encourage the body to burn stored fat for energy. During the fasting window, strict adherence to zero-calorie intake is key, though some variations, known as "dirty fasting," permit minimal calories from certain sources.

Water Fasting

This is a more restrictive approach, where only water is consumed for a set period, typically 24-72 hours and often under medical supervision. It’s used for detoxification or specific health reasons, but carries more risks, such as dehydration and nutrient deficiencies, if not managed carefully.

The Fasting Window: What to Consume

For most common fasting protocols, especially intermittent fasting, the key is to avoid anything that triggers an insulin response. Here’s what you can safely consume:

Water: Plain still or sparkling water is your best friend. It has zero calories, keeps you hydrated, and helps curb hunger.
Black Coffee: Unsweetened, black coffee contains negligible calories (around 5 per cup) and won't break a fast. The caffeine can also help suppress appetite.
Unsweetened Tea: Green tea, black tea, and most herbal teas are excellent choices. Just ensure they contain no added sugar, milk, or artificial sweeteners.
Bone Broth: While it contains calories, bone broth is often used during longer fasts or for "dirty fasting" to replenish electrolytes and nutrients. It typically won't significantly spike insulin, but it does technically break a fast.
Electrolytes: For longer fasts, plain electrolyte supplements (without sugar or calories) or adding a pinch of salt to your water can prevent fatigue and dehydration.

What Definitely Breaks Your Fast

Any food or drink that contains calories will disrupt the metabolic state of fasting. This includes obvious culprits and some less obvious ones:

Sugary Drinks: This category includes regular soda, fruit juices, and sweetened teas or coffees. The high sugar content causes a rapid spike in blood sugar and insulin.
Alcohol: All alcoholic beverages contain calories and interfere with ketosis and fasting benefits. They should be avoided entirely during the fasting window.
Milk, Cream, and Sugar: Adding these to your coffee or tea introduces calories and sugar, effectively breaking your fast. Even small amounts can have an impact.
Processed Foods: Packaged snacks, microwave meals, fried foods, and refined carbs are high in calories and offer little nutritional value. They are counterproductive to fasting goals.
Most Supplements: Gummy vitamins and protein powders contain calories and will break a fast. Check labels carefully. Some non-caloric supplements like creatine are fine, but fat-soluble vitamins (A, D, E, K) are best taken with food for optimal absorption.

Fasting vs. Fast-Friendly Items


Item	Fasting Window (Strict Fast)	Fasting Window (Flexible IF)	Notes
Water	✅ Yes	✅ Yes	The most essential item.
Black Coffee	✅ Yes	✅ Yes	Small amounts of calories (~5) are generally tolerated.
Herbal Tea	✅ Yes	✅ Yes	Ensure no added sweeteners.
Bone Broth	❌ No	✅ Sometimes	Technically breaks a fast, used for electrolytes on longer fasts.
Diet Soda	❌ No	❌ Best to Avoid	Artificial sweeteners may trigger insulin or cravings.
Milk/Creamer	❌ No	❌ No	Contains calories that break a fast.
Fruit Juice	❌ No	❌ No	High in sugar; causes insulin spikes.
Protein Powder	❌ No	❌ No	High in calories and protein that stimulate insulin.
Sugar-Free Gum	❌ No	✅ Sometimes	May trigger a minor insulin response via cephalic phase.

What to Eat to Break Your Fast Gently

How you reintroduce food is as important as the fast itself, particularly for longer fasts. Starting with a large, heavy meal can cause digestive issues like bloating and nausea. Follow a gradual approach:

Start with Fluids: Rehydrate with water, bone broth, or diluted lemon water.
Ease in with Easily Digestible Foods: Begin with small portions of soft, nutrient-dense foods like vegetable soup, cooked vegetables, or fermented foods (e.g., plain yogurt or kefir).
Introduce Lean Proteins and Healthy Fats: After a light starter, incorporate lean protein sources like eggs, avocado, or fish.
Listen to Your Body: Pay attention to how your body reacts and don't rush back into a full meal. Gradually increase portion sizes and food variety.

Your Eating Window: Maximizing Nutrients

During your eating window, the goal isn't to overindulge but to refuel with healthy, nutrient-dense foods that support your goals. Prioritize whole foods over processed ones.

Lean Protein: Fill up on sources like chicken, fish, eggs, tofu, and legumes to maintain muscle mass and promote satiety.
Healthy Fats: Incorporate healthy fats from nuts, seeds, avocados, and olive oil, which can support cognitive function and energy.
Fiber-Rich Fruits and Vegetables: These provide essential vitamins, minerals, and antioxidants. Choose low-glycemic options like berries, leafy greens, and cruciferous vegetables.
Whole Grains: Opt for whole grains such as oats, brown rice, and quinoa for sustained energy rather than the rapid spikes from refined carbohydrates.

Conclusion

Navigating the rules of fasting can seem complex, but the core principle is straightforward: minimize calorie and insulin triggers during your fasting period and refuel mindfully during your eating window. Adhering to this practice, with zero-calorie beverages as your go-to during the fast, can help you achieve your health goals. Always consult a healthcare professional before starting any new dietary regimen, especially if you have underlying health conditions. Understanding what can and can't you have while fasting is the first and most important step toward success.

Visit Healthline for more detailed information on various fasting protocols.

Frequently Asked Questions

While zero-calorie, artificial sweeteners technically contain no calories, they can sometimes trigger an insulin response or increase cravings. It is best to avoid them during a strict fast.

Chewing gum, especially with sugar or artificial sweeteners, can stimulate digestive processes and potentially break a fast. It is generally recommended to avoid it to stay safe.

Dirty fasting is a less strict form of fasting where you consume a minimal amount of calories during the fasting window, often from sources like bone broth or healthy fats (e.g., MCT oil). This might help with satiety but technically breaks a true fast.

Supplements that contain calories, sugar, or protein, such as gummy vitamins and protein powder, will break a fast. Individual micronutrients or creatine are often acceptable, but fat-soluble vitamins should be taken with food for better absorption.

Staying well-hydrated with water, black coffee, or herbal tea can help. Keeping busy and distracting yourself is also an effective strategy. For some, a small amount of bone broth or healthy fats during a "dirty fast" can also help.

The best foods are hydrating, easily digestible, and nutrient-dense. Good options include bone broth, soft-cooked vegetables, fermented foods like yogurt, and lean proteins.

Yes, avoid heavy, fried, or sugary foods immediately after a fast. These can cause digestive distress, bloating, and blood sugar spikes. It's better to introduce foods gradually and mindfully.