Dirty fasting is a type of time-restricted eating. Here’s what you need to know about the trend and whether it’s an effective weight-loss technique.

Many people like to do intermittent fasting, which means taking breaks from eating regularly. There are different ways to do this. One way is alternate-day fasting, where you eat calories every other day. Another way is time-restricted eating, where you eat calories only during a specific time, usually 6 to 10 hours. Fasting is not a new concept. People have been doing it for a really long time. They used to do it for religious or cultural reasons, but now some people are using it to help with weight control. They say it also has other benefits like managing blood sugar, reducing inflammation, and keeping the brain healthy.

Dirty fasting is a specific type of time-restricted eating that allows you to consume about 100 calories during your daily fasting periods. Here is what you need to know about dirty fasting, how it works, and whether it is an effective weight-loss technique.

What Is Time-Restricted Eating?

Time-restricted eating is about controlling when you eat during the day, limiting it to a specific time frame, like 12, 10, or 8 hours. For example, there’s a method called 16:8, where you fast for 16 hours and eat during an 8-hour window. So, you might not eat from 8 p.m. to noon and then eat from noon to 8 p.m. During the fasting hours, you can only have drinks with no or very few calories, like water, black coffee, tea, or unsweetened herbal tea. This is often called “clean fasting.

According to a study from 2021, the idea behind time-restricted eating is connected to our body’s internal clock, known as the circadian clock. This clock is closely linked to our body’s metabolism, and when we eat plays a role in how our metabolism works. There are some evidence suggesting that clean fasting might have benefits such as improved heart health, lower blood pressure and blood sugar, and weight loss. Another study found that eating during an eight-hour window from 7 a.m. to 3 p.m. could be effective for losing weight and body fat.

What Is Dirty Fasting?

Dirty fasting is a variation of time-restricted fasting where people consume a limited number of calories or specific foods during the established fasting window. The primary objective is to maintain fasting principles while achieving outcomes comparable to those of a clean fast. Dirty fasting involves the intake of some calories within the fasting window. It is different from traditional fasting practices where all foods and calorie-containing beverages are restricted. People practicing dirty fasting typically consume up to 100 calories, often in the form of milk and sweetener in coffee or a cup of bone broth.

The term “dirty fasting” is not declare within the medical community, and a standardized definition is lacking. Variability exists in the number of calories consumed during a dirty fast, with advocates suggesting that a modest caloric intake does not negate the fasting benefits, potentially making adherence to a fasting regimen more feasible. Within the context of intermittent fasting (IF), dirty fasting is a modified approach. Intermittent fasting encompasses patterns of limited or no calorie intake alternating with periods of normal energy consumption. Traditional intermittent fasting methods involve complete abstinence from calories during fasting periods, typically lasting 12 to 24 hours. Dirty fasting deviates by allowing some calorie intake, representing a modified fasting practice.

How Does Dirty Fasting Work?

Fasting means not taking in calories. Some studies suggest that eating in specific time periods has changed what it means to be in a fasting state, not just in terms of calories. In simple terms, even if your cells don’t react the same way they do when you have eaten, it might still be considered a form of fasting, especially in “dirty fasting.” During fasting, your body has low calories and carbohydrates, leading to a drop in insulin levels. This, in turn, causes hormones like glucagon and epinephrine to increase. These hormones prompt the release of stored fat from fat cells.

Some of this released fat goes to the liver, where it turns into ketones and goes back into the bloodstream. These ketones become a source of energy for the brain instead of the usual glucose. Fasting at a physiological or molecular level continues if glucose and insulin stay low while ketone levels remain high. However, we can achieve this fasting state with limited calories allowed in a dirty fast.

What Are the Rules of Dirty Fasting?

Different people have different opinions on the rules of dirty fasting. Some websites supporting dirty fasting say it’s okay to have any food or drink during fasting, as long as it is under 100 calories. On the other hand, some sources only approve of high-fat foods because they don’t cause an immediate spike in insulin. Certain dirty fasting approaches allow the use of artificial sweeteners since they have zero calories. However, a study from 2017 found that these sweeteners might increase insulin levels, even if you just taste them and don’t swallow. Others who follow dirty fasting might include higher-protein foods like bone broth or collagen during the fasting period. But a study from 2021 suggested that lower protein intake might be more effective in avoiding the activation of metabolic pathways that sense nutrient availability.

Most suggestions for dirty fasting are based on theories and not on clinical research. As of November 2022, there are not any scientifically proven rules about what you can eat during the fasting hours, as more research is needed to understand how different foods, macronutrients, ingredients, and calorie intake affect the body during dirty fasting.

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Is Dirty Fasting Effective?

Many people interested in dirty fasting want the health benefits of time-restricted eating but also the freedom to consume something with calories during the fasting period. Evidence of dirty fasting believe that this flexibility makes it easier to stick to the fasting routine because there are fewer restrictions and less hunger. For instance, some people find that time-restricted eating helps them avoid overeating, maintain a consistent eating schedule, and practice mindful eating. However, they may miss having a nut milk latte in the morning, which is typically not allowed in a traditional clean fasting approach. Dirty fasting allows for some flexibility in enjoying such treats.

There are some evidence supporting the effectiveness of dirty fasting. In a 2021 study, participants were given water, a traditional breakfast, or a Fast Bar after a 15-hour overnight fast. Fast Bars, made from nuts, seeds, vegetable fiber, and honey, provide around 200 calories, low protein content, a low glycemic index, around six grams of net carbohydrates, and 17 grams of fat. The study found that the group consuming the Fast Bar had glucose levels similar to the water-only group and maintained ketone levels comparable to the water-only group after two or more hours. In contrast, the group eating breakfast experienced a spike in glucose and reduced ketones. Fast Bar eaters also reported feeling full and had a decreased desire to eat compared to the water-only group.

Regardless of the physiological effects, there may be psychological or behavioral benefits to dirty fasting. For example, nibbling on something in the morning might prevent overeating later in the day, and knowing what you can consume helps you get through the end of a fasting window, even if you don’t necessarily need the food or drink.

Should you try dirty fasting?

If you are thinking about trying intermittent fasting, it is good to choose a method that has scientific support for its effectiveness, like time-restricted eating. In this approach, you consume all your calories within a specific time frame, such as a 6- or 8-hour window, and fast for the remaining 16–18 hours. To ensure you are in a true fasting state, avoid consuming any calories during your fasting window. However, most experts agree that minimal calories in beverages like black coffee and herbal teas usually don’t disrupt the fasting state.

While intermittent fasting has various health benefits. However, it is not necessary for improving health. Whether your goal is to lose body fat, reduce disease risk, or increase longevity, there are alternative ways to achieve these objectives without following fasting protocols. If you are considering intermittent fasting, it is advisable to refer to a comprehensive guide and, importantly, consult with a good dietitian or a medical professional. They can help you determine whether intermittent fasting is the right choice for your specific needs and health goals.

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Who Should Try Dirty Fasting?

Note that dirty fasting is not suitable for everyone. In general, children, pregnant and breastfeeding women, individuals taking specific medications, those with eating disorders, and people who are underweight should avoid fasting. Additionally, there is no evidence suggesting that dirty fasting is more effective for weight loss and metabolic health improvement than traditional methods such as reducing overall calorie intake during meals. However, if you are curious about trying intermittent fasting (IF), dirty fasting might provide a way to ease into IF without completely avoiding calories during the fasting period. Whether you choose traditional IF or dirty fasting, it’s advisable, especially for newcomers to intermittent fasting, to start with a shorter fasting window. This approach allows you to observe how your body responds to longer periods with limited calorie intake.


Many people following this method aim to consume about 100 calories during the fasting window, focusing on foods and drinks that are low in carbs and higher in fat. This preference for lower-carb options is because foods and drinks with higher carbs, like fruit, soda, juice, and grains, can have a more significant impact on blood sugar and certain hormones, such as insulin.

Here are some examples of foods and drinks that align with this approach:

  1. Coffee or tea with heavy cream
  2. Bone broth
  3. Nonstarchy vegetables like broccoli
  4. Low-calorie, low-carb soups like vegetable soup

It’s important to remember to stick to around 100 calories during the fasting window when using this method. Regardless of the foods and drinks you choose, it’s essential to be mindful of your portions to avoid consuming too many calories. This means keeping an eye on both healthy and less healthy high-calorie options to stay within the desired calorie range.


One of the attractions of time-restricted eating is that, in addition to weight loss, it may provide additional health benefits. However, experts emphasize that the quality of the food you eat during non-fasted hours (including the brief dirty fasting windows) is important. Nutrition remains a key factor. It is important to include a variety of vegetables, fruits, and other whole foods daily to ensure you are getting a good mix of vitamins, minerals, fiber, antioxidants, and macronutrients.

Whether your goal is weight management or overall health, the ultimate objective is to establish a sustainable long-term routine. Intermittent fasting or time-restricted eating is about finding a balance between restricting and nourishing, not just focusing on the former. If dirty fasting seems like a healthy compromise and fits well with your lifestyle and relationship with food, it might be the best approach for you. The key is to find a routine that is sustainable and promotes both your health and well-being.

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