Intermittent fasting is a popular practice that involves regularly engaging in periods of fasting, or not consuming calories, and a few types exist.

Alternate-day fasting refers to when you consume calories every other day. Also, time-restricted feeding — when you consume calories within a specific period or “feeding window,” typically lasts 6–10 hours and has grown in popularity in the last decade (1, 2).

Dirty fasting is a new practice being used by some people who engage in intermittent fasting.

This article explains what dirty fasting is, how it works, and whether it’s effective.

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Before diving into what dirty fasting is, it’s important to note that the term isn’t used in the medical community. There’s no research on this practice or how it compares with “clean” fasting.

Dirty fasting is a term used to describe consuming some calories during a fasting window.

This differs from traditional fasting or “clean” fasting, which restricts all foods and calorie-containing beverages.

People who practice dirty fasting will typically consume up to 100 calories during their fasting window. This may include some milk and sweetener in their coffee or a cup of bone broth.

Again, there’s no set definition of dirty fasting, so some people may consume many more calories during a dirty fast, while others may consume fewer.

On the other hand, people who practice traditional methods of fasting, or “clean” fasting, don’t consume any calories during fasting windows.

An exception to this is modified alternate-day fasting, in which you consume a small number of calories, typically 500 or so, on “fasting” days (3).

Advocates of dirty fasting suggest that having a small number of calories doesn’t technically “break” a fast and that this method of fasting makes it easier to maintain a fasting regimen.

Summary

Dirty fasting is a term for consuming a small number of calories during a fasting window. This differs from traditional or “clean” fasting, a method in which you don’t consume any calories during fasting windows.

Dirty fasting is technically modified fasting, meaning that you consume a small number of calories during fasting windows.

Although you’re still consuming some calories, any sort of calorie restriction will result in health benefits.

For example, if weight loss is your goal, dirty fasting can promote fat loss. This is simply because you’re likely consuming far fewer calories when dirty fasting than you would during a typical day of eating without time restrictions.

However, some people use intermittent fasting for the other benefits that fasting offers, including promoting autophagy, reducing insulin resistance and blood sugar levels, and more (4, 5).

Autophagy is a process that involves the programmed “cleaning” of cells. It’s an important process that’s necessary for maintaining healthy cellular function and preventing disease.

There’s no evidence that dirty fasting is as effective as traditional fasting methods — which involve complete calorie restriction during fasting periods — for promoting these potential benefits.

While consuming a splash of milk in coffee or a cup of bone broth isn’t the same as having a full meal, technically, you’re not fasting if you’re taking in calories, no matter whether it’s a small number.

Most experts agree that although taking in zero calories is the only way a person can be sure they’re truly in a fasted state, zero-calorie beverages like black coffee aren’t likely to break a fast.

However, drinking coffee with cream, milk, sweetener, or other calorie-containing beverages may break a fast.

Modified alternate-day fasting, which involves calorie intake during fasting windows, has been linked to some health benefits, including weight loss and reduced inflammatory markers, blood pressure, and cholesterol.

However, this practice is different than other types of intermittent fasting, which include complete calorie restriction during fasting periods (6).

This means that it may not have the same effects as traditional fasting methods that involve zero calorie intake during fasting periods. Similarly, dirty fasting should be considered a modified type of fasting.

Again, there’s no research specifically on dirty fasting. It’s likely that people who practice dirty fasting may not technically be in a fasted state during fasting windows, especially if they’re consuming more calories than they realize.

Summary

Dirty fasting is technically a modified type of fasting. The only way to ensure you’re in a fasted state is to abstain from all calories during a fasting window. For this reason, dirty fasting may not have the same effects as “clean” fasting.

If you’re interested in intermittent fasting, it’s best to choose a method that has research backing its effectiveness over dirty fasting, such as time-restricted eating — where you consume all of your calories within a specific timeframe (7).

For example, some people may choose to eat within a 6- or 8-hour window and fast for the remaining 16–18 hours.

The only way to ensure that you’re in a fasted state is to take in zero calories during your fasting window. However, most experts agree that the negligible number of calories in drinks like black coffee and herbal teas won’t break your fast (8).

Although intermittent fasting has been linked to a number of health benefits, it’s important to know that intermittent fasting is unnecessary to improve health.

Whether you want to lose body fat, reduce your disease risk, or increase your longevity, there are many other ways to achieve these goals without using fasting protocols.

If you’re interested in trying out intermittent fasting, check out this comprehensive guide.

Working with a registered dietitian can also help you decide whether intermittent fasting is the right choice for your specific needs and health goals.

Summary

If you’re interested in trying intermittent fasting, stick with a method that has research to back its potential benefits, such as time-restricted feeding, and speak with a medical professional or registered dietitian first.

Dirty fasting involves consuming a small number of calories during fasting windows.

Proponents of dirty fasting suggest that this method makes sticking to fasting regimens easier, but dirty fasting is not technically fasting. If you’re taking in calories — no matter whether it’s a small number — you may break your fast.

The only way to ensure you’re in a fasted state is to forgo all calories during your fasting window.