Can I Drink Zero Drinks While Fasting? Understanding the Metabolic Impact

December 20, 2025 •

4 min read

According to a 2017 review, approximately 41% of American adults and 25% of children consume low or zero-calorie sweeteners, highlighting their prevalence. This raises the critical question for those practicing intermittent fasting: can I drink zero drinks while fasting without compromising my health goals?

Quick Summary

The impact of zero-calorie drinks during fasting depends on the ingredients and your specific health goals. While they are calorie-free, artificial sweeteners can trigger an insulin response or affect the gut microbiome in some individuals, potentially disrupting the metabolic benefits of fasting. Safer options include water, black coffee, and unsweetened tea.

Key Points

Check Your Fasting Goals: For weight loss, zero-calorie drinks may be acceptable, but for maximizing metabolic benefits like autophagy, stick to water and unsweetened beverages.
Artificial Sweeteners are a Gray Area: The impact of artificial sweeteners on insulin and gut health is debated and varies by individual, so monitor your body's response carefully.
Water is the Safest Option: Plain water, both still and sparkling, is the gold standard for hydration during any fast.
Black Coffee and Unsweetened Tea are Generally Safe: These calorie-free options can help with energy and hunger, provided they have no additives.
Listen to Your Body: Pay attention to how zero-calorie beverages affect your hunger and cravings to determine what works for your unique metabolism.
Read Labels Carefully: Always check for hidden sugars, artificial sweeteners, and other additives that might interfere with your fasting state.

The Core Principle: Calories, Insulin, and Fasting Goals

To understand the relationship between zero-calorie drinks and fasting, it's essential to grasp the core metabolic principles at play. Fasting is the deliberate avoidance of caloric intake for a set period, which encourages the body to switch from burning sugar for energy to burning stored fat in a state known as metabolic switching. A primary goal is keeping insulin levels low and stable, which is crucial for promoting fat burning and activating cellular repair processes like autophagy.

The Debate Over Zero-Calorie Sweeteners

This is where the gray area for zero-calorie drinks emerges. While they contain no caloric energy, many depend on artificial sweeteners like aspartame, sucralose, or acesulfame potassium to provide a sweet taste. Scientific opinion is divided on how these substances affect the body during a fast.

Insulin Response: Some studies suggest that the sweet taste can trigger a cephalic phase insulin response, where the body, anticipating sugar, releases a small amount of insulin. While a negligible amount of insulin may not immediately 'break' a fast, it can slightly inhibit the body's fat-burning processes. Individual responses vary, and some people are more sensitive to this effect than others.
Gut Health: Research indicates that artificial sweeteners may negatively impact the gut microbiome, which plays a crucial role in overall metabolic health. Changes in gut bacteria could potentially alter glucose tolerance and influence hunger hormones, leading to cravings.
Cravings: For some, consuming a sweet-tasting, zero-calorie drink can intensify cravings for sugary foods, making it harder to stick to the fasting plan in the long run.

Making Informed Choices: Zero vs. Whole

Given the conflicting evidence and individual variability, the best approach is to align your drink choices with your specific fasting objectives. A 'clean fast' involves consuming only water to maximize the benefits of autophagy and metabolic reset, but for most people, a more lenient approach is fine.

Fasting-Friendly Beverage Options

Plain Water (Still or Sparkling): The undisputed champion of fasting hydration, containing zero calories and no additives. Sparkling water can also help reduce feelings of hunger.
Black Coffee: With minimal calories, black coffee is a popular choice that can enhance mental alertness and fat oxidation. Avoid sugar, milk, and creamers.
Unsweetened Tea (Green, Black, Herbal): Offers variety without compromising the fast. Green tea provides antioxidants, while herbal teas like chamomile can be soothing.
Diluted Apple Cider Vinegar: A small amount mixed with water can potentially help with cravings and has minimal caloric impact.

The Gray Area and What to Avoid

Many pre-packaged zero-calorie options fall into a gray area. While calorie counts are minimal, the presence of artificial ingredients can complicate matters. Common examples that require caution include:

Diet Sodas (e.g., Coke Zero): Contains artificial sweeteners like aspartame and acesulfame potassium that may trigger an insulin response in some individuals.
Flavored Sparkling Waters with Sweeteners: Always check the label, as some contain sweeteners or a small amount of fruit juice concentrate.
Energy Drinks (Zero-Sugar): Often contain artificial sweeteners and high levels of caffeine, which can impact cortisol levels and sleep.

Comparison of Fasting Drinks


Drink	Caloric Impact	Potential Fast Disruption	Best For	Considerations
Plain Water	None	None	All fasting goals, especially clean fasting.	Optimal hydration and metabolic function.
Black Coffee	Minimal (<5 kcal)	Minimal	Boosting energy and focus during a fast.	Avoid additives; monitor caffeine intake.
Unsweetened Herbal Tea	None	None	Hydration and variety, especially in the evening.	Ensure no added sugars or flavors.
Diluted Apple Cider Vinegar	Minimal (<5 kcal)	Minimal	Curbing appetite and supporting digestion.	Must be diluted to protect tooth enamel.
Diet Sodas	Zero	Possible (variable)	Weight loss goals where minor metabolic effects are acceptable.	Individual response to artificial sweeteners varies; may trigger cravings.
Bone Broth	Low (some kcal)	Moderate	Extended fasts to replenish electrolytes.	Technically breaks a 'clean' fast; not suitable for autophagy focus.

Conclusion: Personal Goals Dictate the Rules

Ultimately, the question of whether you can drink zero drinks while fasting depends on your specific goals. For weight loss, where the primary driver is calorie reduction, the minimal impact of artificial sweeteners might be acceptable, especially if it helps you adhere to your fasting schedule. For those pursuing more advanced metabolic benefits, like maximizing autophagy or improving insulin sensitivity, a stricter approach—sticking to water, black coffee, and unsweetened tea—is the safest bet. Listen to your body and observe how different beverages affect your hunger levels and overall well-being. Consulting a healthcare professional for personalized guidance is always recommended.

Making the Best Choice for You

To navigate the options, start with the most conservative choices like water and unsweetened herbal teas. If you desire variety, introduce black coffee or pure sparkling water. If you experiment with diet sodas, pay close attention to your body's response, including any changes in cravings or hunger levels. Remember, fasting is a personal journey, and what works best is what you can consistently maintain while reaching your health objectives.

Frequently Asked Questions

Not necessarily, but it depends on your fasting goals. Strictly speaking, calorie-free drinks won't break a fast from a caloric perspective. However, some artificial sweeteners in diet sodas and flavored waters can trigger a minor metabolic response, potentially impacting the deeper benefits of fasting.

Coke Zero, like other diet sodas, contains artificial sweeteners that may trigger an insulin response in some people, potentially disrupting the metabolic state of your fast. While it won't add calories, purists aiming for maximum benefits often avoid it.

Plain sparkling water is a perfectly fine choice during a fast, as it contains zero calories and no additives that affect your metabolism. The carbonation can also help curb hunger pangs.

Most unsweetened flavored sparkling waters are acceptable for fasting, but it is critical to check the label. Ensure there are no artificial sweeteners, fruit juice concentrates, or other hidden caloric ingredients that could potentially affect your fast.

Research on this is mixed and individual responses vary. Some studies suggest that the sweet taste can lead to a small cephalic phase insulin release, even without calories. For those concerned with insulin control, it's best to avoid them during fasting.

For a 'clean fast,' where the goal is to maximize metabolic reset and autophagy, the best drinks are plain water, black coffee, and unsweetened tea. These options are free of calories and additives that might interfere with fasting processes.

While diet sodas won't kick you out of ketosis from a carb perspective, the artificial sweeteners can trigger cravings and potentially disrupt gut health, making it harder to stick to the diet long-term. For best results, it is often recommended to avoid them.