You might hear people talk about good diets and bad diets, clean ones and dirty ones. But just like a diet, fasting can be dirty or clean, too! The difference is widely discussed online and while “clean” and “dirty” are not medical terms, they are used in the fasting community.
Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and fasting. It doesn’t dictate what you eat (no restrictions on what you eat i.e., no carbs, no sugar, etc.), but rather when you eat.
With clean fasting, everything is clear: when you fast, you fast. Clean fasting means you consume no calories during the fast and typically only drink zero-calories drinks like water, black coffee, plain tea with no milk or sweeteners. From the metabolic perspective, this is the most “pure” fast as it keeps insulin at baseline, maximizes fat oxidation and allows autophagy to occur more fully. Even small amounts of calories (especially carbs or protein) can spike insulin levels, reduce fat burning and suppress autophagy.
What is dirty fasting?
But how dirty is dirty fasting? Despite the name, it doesn’t imply you can have a burger and chips halfway through your fast. What it means is that you can consume small amounts of calories during a fasting window, for example, have cream or milk in your coffee, artificial sweeteners, sugar-free gum, bone broth, MCT oil or butter, zero-calorie drinks (they may still trigger insulin in some people). Usually, people who opt for dirty fasting consume up to 100 calories during their fast.
Yes, it affects autophagy and insulin, but it might help one to improve consistency and still be in an overall calorie deficit. This approach is more flexible than traditional fasting methods, making it easier to stick to for weight loss and overall health benefits. However, although 100 calories does not sound like much, it’s still important to understand what foods and drinks you can have during the fasting window, and what the science behind it is.
Insulin, calories, and taste
When we talk about fasting, three factors play a key role: insulin, calories, and taste. Knowing how these interact helps us understand why some foods “break” a fast more than others.
Insulin
Insulin is a hormone that helps glucose from the blood enter cells. When insulin levels are low, the body burns stored fat for energy more easily. This is why fasting is often associated with fat burning and improved blood sugar control. Carbohydrates and protein tend to cause a significant increase in insulin, while fats have a much weaker effect.
| While insulin is high: Fat is not really being burned The body uses food rather than its fat reserves | While insulin is low: The body begins to use fat reserves It’s easier to enter fat-burning mode |
Calories
Calories are important, but they are not the only factor. Biologically, any caloric intake formally ends the fast. However, in real life, it’s not just the caloric content itself that matters, but also the type and quantity. A small amount of fat, such as cream in coffee, can cause a much smaller hormonal response than sugar or milk. This is why some people use elements of dirty fasting to make fasting more comfortable and sustainable.
Taste
Taste also plays a role in dirty fasting, even when there are no calories. Sweet taste, including artificial sweeteners in sugary beverages, can trigger a cephalic response. The body anticipates the arrival of food, and for some, this can lead to a small insulin surge or increased hunger. The response to this varies greatly from person to person, which explains why some people tolerate sweeteners well while others don’t. Research on this shows that taste alone can trigger anticipatory hormonal and metabolic responses, including insulin release, before nutrients enter the bloodstream.
Fasting can be very challenging, not just physically but also mentally. So if you think that having a zero-calorie beverage during your fasting window is a good idea, paradoxically, it might make fasting harder. Diet sodas, flavored waters, artificially sweetened electrolyte mixes, and other “calorie-free” drinks keep the senses busy during the fast. Reviews of non-nutritive sweeteners suggest that sweet taste without calories may alter reward and satiety signalling in ways that actually prolong food-seeking behaviour, particularly in sensitive individuals.
This means that you might want to consider a psychological factor of dirty fasting. Sensory cues such as sweetness, flavour, and stimulation are closely tied to eating behaviour. Even when you are not actually consuming calories, exposure to tastes can reinforce food-seeking signals in the brain and keep the body in a “fed” state, making practicing dirty fasting even more effortful and hard, when all you can think about is food.
Some studies demonstrate that non-caloric sweeteners such as sucralose can increase activity in the hypothalamus, a key brain region involved in appetite regulation, blood sugar control, and energy balance, more than either sugar-sweetened drinks or water. In simple terms, it means that when sweetness is detected without the expected caloric intake, the brain continues to signal hunger rather than reducing appetite, making consuming zero-calorie beverages feel counterproductive for people trying to curb hunger, promote weight loss, or limit their calories consumed during clean or dirty fasting.
Black coffee
Even those who prefer clean fasting drink black coffee, but, interestingly, when consumed on an empty stomach, it can produce a similar effect in some people practising intermittent fasting. Caffeine increases gastric acid secretion and stimulates cortisol, a stress hormone that can amplify hunger signals and influence insulin levels, leading to stomach discomfort and cravings.
Herbal tea
Herbal tea is another great example of this. Unlike traditional black or green tea, herbal teas are made from flowers, fruits, or aromatic plants that give them their sweet aromas that can stimulate digestive activity and insulin response, even though they contain zero calories. For some individuals, this sensory stimulation may increase gastric secretion and trigger stomach rumbling or cravings, making it harder to sustain prolonged fasting or to avoid consuming calories, particularly during time-restricted eating.
Electrolytes
Electrolytes are a special case. Hydration and mineral balance are obviously very important during fasting periods (we aren’t trying to do a dry fast!), especially with prolonged fasting, alternate-day fasting, or increased physical activity. Electrolytes themselves do not contain sugar. It’s all about sweetened electrolyte drinks that add carbohydrates into the mix, hence raising insulin levels, affecting blood sugar, and clearly breaking a fast, even a dirty one, by increasing overall caloric intake. Hydration matters, but plain water, mineral water, or unsweetened electrolyte formulations support hydration just fine without messing with insulin sensitivity and without affecting fat loss and other fasting benefits.
This is something that people often overlook. Both clean and dirty fasting are shaped not only by calories and insulin, but also by perception. Limiting sweet or highly stimulating zero-calorie beverages during a fasting window mayactually help reduce hunger and make intermittent fasting more sustainable for weight management, fat loss, and metabolic health.
Autophagy: What We Know and What We Don’t Know
When our cells grow old and start to accumulate damage, it contributes to oxidative stress, a state linked to progressive inflammation, ageing, and disease. Autophagy is a natural cellular cleansing process in which cells break down and recycle damaged or unnecessary components. This mechanism is important for maintaining cellular health and is often cited as one of the benefits of fasting.
What we know so far:
Autophagy is closely linked to nutrient availability. When food is not availble, and insulin levels drop, the body shifts its focus from growth to maintenance and repair. Animal studies show that fasting significantly enhances autophagy. Humans also show changes in biomarkers indicating their activation during prolonged calorie restriction or fasting.
What we don’t know yet:
Currently, there is no definitive answer to the question of how many hours of fasting it takes for autophagy to “turn on” in humans. This process is influenced by age, physical activity level, overall metabolic health, and diet. It is also unknown what specific amount of calories or what foods can significantly affect autophagy. Assessing this process in humans is difficult, so data remains limited
While a precise number of fasting hours for autophagy has not been identified yet, some experts suggest it can begin to increase after 14–18 hours without food, with more noticeable effects potentially occurring around 24-48 hours, because when we look at animal studies, they show that autophagy begins after at least 24 hours of fasting.
So why follow strict rules if we don’t fully understand the science behind it (yet!)? Clean fasting likely creates a stronger signal for autophagy, but this doesn’t mean dirty fasting is ineffective. For most people, long-term benefits depend primarily on overall health and how committed you are to losing weight.
Autophagy is a very interesting process that can be compared to cleaning your house. If you want to learn more about it in the context of intermittent fasting, check an article written by our in-house medical professional.
How to Practice Dirty Fasting
To practice dirty intermittent fasting, first, you need to determine your fasting and eating windows. During the fasting period, minimal caloric intake is allowed if it helps you tolerate hunger and maintain your regimen.
Non-caloric beverages, a small amount of bone broth, or fats such as coconut oil are quite commonly used. Just be careful with portion sizes. Consuming too many calories during a fast can reduce fat burning and actually break a fast. Many fasting experts suggest not exceeding 100 calories during your fasting window, which means you may need to measure portions carefully rather than estimating.
It’s equally important to listen to your body. Symptoms such as dizziness, fatigue, or persistent hunger may indicate the need to adjust your approach.
Is Dirty Fasting Right for You?
If you are new to intermittent fasting, primarily focused on weight loss, or already tracking your calorie intake carefully, dirty fasting may be worth trying. For people who can stay within a small caloric range (for example, under 100 calories) without triggering overeating, this flexible approach can make fasting more sustainable.
However, dirty fasting may not be ideal if you struggle with portion control or find that small amounts of calories stimulate more hunger rather than help you suppress it. It may also not be for you if your goal is to experiment with prolonged fasting specifically for autophagy or other cellular adaptations, where stricter fasting protocols are typically recommended.
Breaking a Fast
If you went too far with dirty fasting and really broke your fast, you might want to think about doing it the “right way” because how you break your fast can have a big effect on your energy levels, blood sugar, and weight loss.
You should choose foods that are high in nutrients and don’t produce big increases in insulin. Stay away from sugary drinks, highly processed foods, and high-calorie snacks that make you gain weight. Instead, it’s better to eat full meals like grass-fed meats, vegetables, and healthy fats that help you lose weight.
Metabolic Health and Longevity
While fasting is often perceived as a uniform strategy, in practice, people use it for different purposes. Understanding primary motivation can help you choose the most appropriate format. In the US, intermittent fasting has become quite mainstream over the last few years, and a lot of people come to it for weight loss purposes.
When it comes to metabolic health, for example, improving insulin sensitivity or stabilizing blood sugar, the quality of the fast is more important. Minimizing foods that cause strong hormonal reactions during fasting can be particularly beneficial. Equally important is the type of food consumed during the meal period.
In the context of longevity, discussions often revolve around autophagy and reducing chronic inflammation. However, since data is still limited, extreme or prolonged fasts are not necessary for most of us. Moderation, regularity, and overall health play a much more significant role.
Weight Loss with Dirty Fasting
If your goal is weight loss, a sustainable calorie deficit remains key. Intermittent fasting can help reduce overall food intake by limiting the eating window. In this context, dirty fasting can be effective if it promotes adherence and prevents overeating, as this flexibility is often more realistic and sustainable for many people. However, it’s important to consider factors such as insulin resistance and blood sugar control. What promotes fat loss and metabolic improvements in one person may increase hunger or interfere with insulin regulation in another.
Dirty fasting can be effective for weight loss and reducing body fat because it helps with consuming fewer calories and prolonging fasting periods, allowing the body to more effectively utilize stored fat.
To promote weight loss, it’s essential to maintain a calorie deficit. Combining dirty fasting with a nutrient-dense diet, physical activity, and consistency significantly improves the sustainability of results.
Monitoring Progress
Monitoring your progress is key when practicing intermittent fasting, especially if you prefer a dirty fasting format. Tracking your weight, body fat percentage, energy levels, and other metrics like blood sugar and blood pressure can help you assess the effectiveness of the chosen approach.
Using a food diary or mobile app allows you to monitor your calorie intake, fasting hours, and eating patterns. For personalized recommendations, we also suggest consulting a registered dietitian or other healthcare professional.
Tips for Success
Start with a schedule that works for you and gradually increase fasting hours as your body adapts. During the eating window, prioritize whole, nutrient-dense foods, avoiding processed foods and sugary beverages.
Stay hydrated by drinking water, black coffee, or herbal tea but remember that the sweet tastes of certain teas can increase hunger. Consistency and patience are crucial, sustainable results will take time.
Frequently Asked Questions
How many calories can I consume during a dirty fast?
Typically, up to 100 calories, depending on your goals and individual body response.
What foods and drinks are allowed during dirty fasting?
The most common are coffee with a bit of creamer, bone broth, and sugar-free gum.
Can I practice dirty fasting if I have a medical condition?
If you have a medical condition, consult your doctor before beginning any fasting method.
How long does it take to see results with dirty fasting?
Results vary from person to person, but consistency, calorie control, and patience remain key.
Conclusion
Dirty fasting is a flexible, intermittent fasting option that can promote weight and fat loss and improved metabolic health when approached correctly. Monitoring calorie intake, choosing quality foods, and regularly monitoring your progress increase your chances of success.
As with any diet, the body’s response varies from person to person. Consulting with a specialist is especially important if you have chronic illnesses or concerns about your eating habits. With the right structure and consistency, dirty fasting can be an effective tool for long-term weight management.
