0-Calorie Foods for Fasting: Very Low-Calorie Options to Support Your Routine

True zero-calorie foods are essentially limited to water. Most other 0-calorie foods for fasting actually contain a few calories, but they’re so low that some people enjoy them during certain fasting routines. Whether an item fits your fast depends on the style you follow and your goals. Some modified routines allow up to around 100 calories, while stricter fasts keep things to water alone. Read on to learn what may work for you.

Now let’s dig into the details. 0-calorie foods for fasting are a popular search for anyone who is curious about what they can sip or nibble without feeling like they’ve broken their fast. The honest truth? Outside of plain water, almost nothing is truly calorie-free. But that doesn’t mean you’re stuck with hunger pangs and willpower alone.

This article is for busy people who are exploring fasting and want clear, practical answers without the hype. We’ll break down which drinks, foods, and snacks have ultra-low calories per serving, what “dirty” and “clean” fasting actually mean, and how to choose options that fit your goals.

You’ll find easy-to-scan lists with per-serving calorie details, a simple comparison table, and answers to common questions. Fasting looks different for everyone, so we’ll focus on options rather than rules. If you have health concerns or take medication, it’s always wise to check with a qualified provider before changing how you eat. Ready to separate myth from reality? Let’s go.

Can You Eat 0-Calorie Foods While Fasting?

There are no truly zero-calorie foods aside from water. However, some drinks and foods have so few calories that many people include them during certain fasts.

It depends on the style you follow. Some beverages contain a negligible number of calories and may fit almost any fast. Other low-calorie foods suit modified routines, such as alternate-day or 5:2 approaches, where people eat around 500 calories on fasting days (1).

Popular low-calorie picks include:

• Black coffee
• Unsweetened green tea
• Bone broth
• Raw vegetables
• Zucchini noodles
• Cauliflower rice
• Baked fish
• Oatmeal
• Air-popped popcorn
• Mixed berries
• Eggs

The takeaway here is simple. The phrase “zero-calorie” is more of a friendly shorthand than a literal label. Most of these foods carry a small calorie count, but they’re light enough that some fasting routines make room for them.

Before you feel let down, there’s good news ahead. Plenty of these options are filling, water-rich, and satisfying. So let’s look closer at what zero-calorie foods for fasting really means and where the idea comes from. 

Understanding the details can help you make choices that feel doable, sustainable, and tailored to your own routine rather than someone else’s rigid plan.

Are Zero-Calorie Foods for Fasting a Myth or Fact?

Zero-calorie foods for fasting are a myth. There are very few foods or beverages with literally zero calories. Many are effectively zero-calorie as they contain only trace amounts that can be rounded down on labels. Very low-calorie items can play a role in some fasting styles.

The idea of 0-calorie foods for fasting tends to come up alongside a routine called dirty fasting. Dirty fasting is a relaxed take on time-restricted eating.

With time-restricted eating, you fast for a set number of hours each day and eat within a defined window. A common example is a 16-hour fast with an 8-hour eating window (16:8) (2). Many people fast overnight and eat during the day.

Dirty fasting allows a small number of calories, usually around 100, during the fasting period. The thinking is that a tiny amount of food may help you stay comfortable without fully stepping away from the fasting mindset. If your main goal is overall calorie reduction, a small number of calories during the fasting window may still fit some modified approaches, depending on the total intake.

BetterMe can help you add more structure to your daily wellness routine with workouts, meal planning tools, and habit-building features. Explore the app and take a practical step toward a routine that feels more manageable for you.

What Does Research Say About Intermittent Fasting?

Researchers have reviewed many studies to understand whether intermittent fasting offers benefits. One idea often mentioned is the metabolic switch, where the liver may convert fat into ketones for energy instead of relying on glucose (3).

Intermittent fasting generally means alternating periods of normal eating with periods of minimal or no calories. The overall effect tends to be a reduced calorie intake across the day or week (4).

Some research has explored associations between intermittent fasting, body weight, and metabolic markers, but results vary (5). That being said, results are limited. Many trials have focused on middle-aged adults carrying extra weight, and long-term effects in humans aren’t well understood.

It’s also worth noting that most studies don’t separate “clean” from “dirty” fasting. These are casual, everyday terms rather than formal categories used in research.

Are There Real Differences Between Clean and Dirty Fasting?

Yes, the main difference is calories. So-called clean fasting keeps you to water and other essentially calorie-free options, while dirty fasting allows a small amount, often up to around 100 calories.

Some research on alternate-day fasting, which usually involves around 500 calories on fasting days, has pointed to possible improvements in certain metabolic markers (6). Other reviews have compared alternate-day routines, time-restricted eating, and religious fasting styles, but findings vary by study design and population (7). One important consideration is that changes in overall calorie intake and body weight can influence some metabolic markers, so fasting strictness isn’t the only factor researchers consider.

For dirty fasting specifically, one small randomized trial found that a specially formulated 200-calorie energy bar didn’t appear to halt the metabolic switch for participants (8). Keep in mind that this study was funded by the bar’s manufacturer, which is worth considering when weighing the findings.

The honest summary? The clean versus dirty debate hasn’t been studied in depth—both are flexible interpretations of fasting rather than strict science. What matters most is finding an approach you can stick with comfortably. Let’s keep going and look at whether any food truly comes in at zero calories.

Understanding Very Low-Calorie Foods

No food is truly zero calories except water, but several foods are low enough that some people treat them as “free” during a fast.

Most foods prompt an insulin response (9), which is often what people mean when they say a fast has been “broken.” Insulin tends to be released when glucose enters the blood and needs to move into cells for energy (10).

Some people add zero- or low-calorie sweeteners to coffee or tea during the fasting window. Interestingly, research has suggested that artificial sweeteners may sometimes trigger an insulin response, but findings are mixed (11).

One small study of adults carrying extra weight found that insulin was released after sucralose was consumed in both liquids and solids, with a larger response from solid foods (12). This was a cephalic phase insulin response, which means that a small amount of insulin was released because the brain perceived the sweet taste, not because any actual glucose was detected in the bloodstream. 

Generally, the evidence is inconsistent on whether and when these sweeteners affect insulin. Because responses can vary, certain sweeteners may affect blood sugar levels for some people, so it’s a good idea to consult a healthcare provider if you have concerns.

On the other hand, a small study found that plain, unsweetened black coffee didn’t appear to change fasting blood work values for participants (13). So some items may not noticeably affect your fasting state, even when they carry a few calories.

The big picture is this: individual responses vary. What feels like a clean fast for one person may differ for another, and that’s completely normal. Consider your personal reasons for fasting and what you are actually trying to achieve when determining if a certain food or beverage fits within your fasting window.

Read more: Green Tea Intermittent Fasting: Benefits and Side Effects

Is There a Snack with Zero Calories?

Not really, but low-calorie snacks can fit a dirty fasting routine that caps calories at around 100. Most foods simply don’t arrive at a true zero.

Popcorn is a popular example. Air-popped popcorn without oil is light, crunchy, and satisfying for very few calories. A cup of it lands at roughly 31 calories (14), which makes it an easy nibble for some modified fasts.

The key is portion awareness. A small handful keeps you well within a dirty fasting range, while a giant bowl adds up quickly. Measuring out a single serving can help you stay on track.

What Food Fills You up Without Many Calories?

Fiber-rich, water-heavy fruits and vegetables tend to fill you up for very few calories (15). Remember, no food is realistically calorie-free, but some make portions feel more satisfying.

Low-energy-density produce packed with fiber and water can help you feel full on minimal calories. Fiber digests slowly, which may help you feel satisfied for longer (15). A grapefruit, for example, is about 90% water with very few calories (16).

Fat is high in energy density, but a small amount may help some people feel full during a fast (17). A 5-gram pat of unsalted butter has around 35.8 calories (18), which is why butter or “bulletproof” coffee is a popular choice in some fasting circles.

That being said, a cup of bulletproof coffee can top 300 calories. Because of this calorie load, it doesn’t really fit even a dirty fast, so it’s worth approaching with caution (19).

Protein is another option that supports fullness. While fiber helps you feel full, a little protein may help you stay full longer (20). Just keep in mind the body can convert excess protein into glucose (21), which may not fit stricter fasting approaches in larger amounts.

Is Dirty or Clean Fasting Better for You?

Neither is clearly “better”, as this distinction hasn’t been well-studied, and the right fit depends on your goals, preferences, and health context. Dirty fasting is a trendy spin on time-restricted eating rather than a proven method.

Some newer research has raised questions about possible long-term effects of time-restricted eating. One large study following thousands of people over many years gained attention for suggesting a possible link between prolonged 16:8 routines and higher cardiovascular risk (22).

However, that study had clear limitations, such as relying on self-reported dietary information and not accounting for other factors that influence health. So it’s far from a final word.

Other research points the other way. Some reviews have suggested that intermittent fasting, particularly alternate-day fasting, may support blood pressure and other markers for certain people (23). A separate review found that calorie restriction may support certain cardiovascular factors too (24). Baseline health, body weight, and overall calorie intake may influence these findings, so the results shouldn’t be reduced to fasting alone.

The bottom line is that the research doesn’t fully agree, particularly on long-term effects. If you have heart concerns, elevated blood pressure, or other risk factors, talk with your healthcare provider before starting a fast.

Read more: Intermittent Fasting and Running: What to Know Before You Start

Clean vs. Dirty Fasting: A Quick Comparison

Here’s a simple side-by-side to help you see how the two approaches differ at a glance.

Use this table as a starting point, not a rulebook. Many people experiment with both styles before landing on a routine that feels manageable. There’s no single informal approach that works for everyone, and your health context matters. If you try fasting, consider starting with a less restrictive approach and adjusting based on comfort and professional guidance when needed.

What Low-Calorie Foods Can You Eat in Larger Amounts?

No food gives you a truly unlimited pass, but very low-calorie options let you eat more generously while staying mindful. Some informal dirty fasting approaches use a limit of around 100 calories.

Below, you’ll find practical lists of drinks, foods, and snacks with per-serving calorie details. Pay attention to cooking methods, serving sizes, and ingredients, as these can change the numbers quickly.

6 Very Low-Calorie Drinks That Are Commonly Discussed for Fasting

Some drinks come close to zero calories, while others carry a small amount. Here are six light options to consider:

• Water: Tap or well water is the truest zero-calorie choice for fasting. Any amount has no calories (25).
• Lemon water: A large glass made by squeezing one lemon wedge in 16 fl oz of water has roughly 1.3 calories (26).
• Apple cider vinegar water: One tablespoon of apple cider vinegar has about 3.13 calories (27). Stir it into a glass of water for a tangy fasting drink.
• Instant black coffee: A teaspoon of instant coffee powder has around 3.53 calories (28). Skip the sweeteners for a near-zero cup.
• Green tea: A 12 fl oz cup of unsweetened green tea has only about 4 calories (29).
• Brewed black coffee: A 6 fl oz cup of brewed coffee comes in just under 2 calories (30).

These drinks are low in calories and are commonly discussed in fasting routines.

12 Very Low-Calorie Foods That Are Sometimes Used in Modified Fasting

This list features edible items with ultra-low calories per serving. Note the cooking methods and portions if you plan to enjoy them during a fast:

• Watercress: A 34-gram cup of chopped watercress has about 3.74 calories, 0.78g protein, 0.03g fat, and 0.17g fiber (31).
• Lettuce: A 36-gram cup of shredded lettuce has roughly 5.4 calories, 0.49g protein, 0.05g fat, and 0.47g fiber (32).
• Swiss chard: A 36-gram cup of chopped Swiss chard has about 6.84 calories, 0.65g protein, 0.07g fat, and 0.58g fiber (33).
• Cucumber: A ½ cup of raw cucumber slices has around 7.8 calories, 0.34g protein, 0.06g fat, and 0.26g fiber (34).
• Radishes: A ½ cup of sliced raw radishes has about 9.28 calories, 0.39g protein, 0.06g fat, and 0.93g fiber (35).
• Zucchini noodles: A cup has roughly 19 calories, 1.4g protein, 0.4g fat, and 1.1g fiber (36).
• Carrot: A small 50-gram raw carrot has about 20.5 calories, 0.47g protein, 0.12g fat, 1.4g fiber, and 44.2g water (37).
• Cauliflower rice: A 100-gram cup has around 25 calories, 1.9g protein, 0.3g fat, and 2g fiber (38).
• Baked fish: A 1 oz piece of boneless salmon when baked has about 54 calories, 5.10g protein, and 3.6g fat (39).
• Bone broth: A cup of beef bone broth has roughly 39 calories, 9g protein, and 1g fat (40).
• Shrimp: A 1 oz serving of plain cooked shrimp has about 28g calories, 6.5g protein, and 0.2g fat.
• Oatmeal: A 100-gram serving cooked in water without salt has around 76 calories, 2.5g protein, 1.5g fat, and 1.7g fiber (43).

5 Very Low-Calorie Snacks That Are Sometimes Used in Modified Fasting

These are low-calorie snacks you might enjoy on a dirty fast. Stick to the suggested portions and cooking methods to keep calories in check:

• Popcorn: An 8-gram cup of air-popped popcorn has about 31 calories, 1.03g protein, 0.36g fat, and 1.16g fiber (14).
• Mixed berries: A ½ cup has roughly 32.5 calories, 0.7g protein, 0.3g fat, and 2.8g fiber (44).
• Rice cakes: A single rice cake has about 11.9 calories, 0.7g protein, 0.3g fat, and 0.4g fiber (45).
• Oranges: A small 96-gram orange has around 45.1 calories, 0.9g protein, 0.12g fat, and 2.3g fiber, plus about 83.3g water (46). Water-dense, fiber-rich fruits may be suitable for some modified fasting routines.
• Boiled eggs: A large hard-boiled egg has about 77.5 calories, 6.3g protein, and 5.3g fat, making it a handy grab-and-go option  (47).

Workouts, weight management tools, and recipe ideas come together in the BetterMe: Health Coaching app, giving you practical support for building a more consistent wellness routine.

Frequently Asked Questions

• Can you eat 0-calorie foods while fasting?

You can include very low-calorie foods during certain modified fasts, such as dirty fasting. True zero-calorie foods don’t really exist outside of water, so most “free” options still carry a few calories. Strict fasts generally stick to water alone.

• What is dirty fasting?

Dirty fasting is an informal, relaxed version of time-restricted eating that often allows up to around 100 calories during the fasting window. Some people use it to manage hunger while still feeling close to a fasting routine. It hasn’t been studied in depth, but if your goal is overall calorie reduction, a small number of calories during the fasting window may still fit some modified routines, depending on total daily or weekly intake.

• What is the lowest-calorie snack for fasting?

Watercress and other leafy greens are among the lowest, with a cup landing under 5 calories. Air-popped popcorn and water-rich produce are also light, satisfying choices. Portion size matters, so measure your servings.

• Can you use sweeteners while fasting?

Some people use zero- or low-calorie sweeteners, but research on low-calorie sweeteners and insulin response is mixed. Responses vary widely, and research findings are mixed, so sweeteners may or may not influence your fasting state. Consider checking with a healthcare provider if you monitor glucose, take medication, or follow a medical nutrition plan.

• Does black coffee break a fast?

Plain, unsweetened black coffee is very low in calories, and one small study found that it didn’t noticeably change fasting blood values for participants (13). Many people include it during fasts. Just skip the sugar, cream, and flavored syrups.

The Bottom Line

Our top 0-calorie foods for fasting aren’t all truly calorie-free, but they’re light enough to keep you satisfied with very little. Outside of water, most options carry a few calories, so the “zero” label is really just friendly shorthand.

If hunger creeps in, some fasting styles make room for a small amount of food. The low-calorie drinks, foods, and snacks on this list may be useful reference points for understanding modified fasting options. If you try fasting, keep the approach conservative and consider professional guidance if you have health concerns.