What Is Dirty Fasting?

 

Dirty fasting is a different approach to intermittent fasting.

Intermittent fasting involves periods of little to no eating. One common way to practice intermittent fasting is through time-restricted eating.

Time-restricted eating requires limiting the hours you eat within a day to a 12-, 10-, or even eight-hour window.

The latter option, also known as the 16:8 intermittent fasting diet, involves a 16-hour fast followed by an eight-hour eating window.

Time-restricted eating helps prevent overeating, maintain a consistent eating schedule and eat more mindfully.

Traditionally, during fasting hours, you only consume beverages with zero or minimal calories—like water, black coffee or tea, and unsweetened herbal tea. This type of fasting is known as "clean fasting."

Clean fasting may offer benefits that include:

• Improved heart health
• Reduced blood pressure and blood sugar
• Weight loss

In a 2021 study published in Frontiers in Endocrinology, researchers explain that the science behind time-restricted eating relates to the circadian clock. Our body's circadian clock is tightly connected to our body's metabolism, and meal timing is an essential factor in metabolism.

Dirty fasting is a specific type of time-restricted eating that allows you to consume about 100 calories during the otherwise clean fasting periods. The goal is to disrupt the concept of fasting as little as possible while achieving similar benefits as a clean fasting. Here is the theory behind dirty fasting:

Fasting is known as the absence of calories. But if the body cells do not react as they likely do during a "fed" state, people can still possibly achieve that fasting state even with the limited caloric intake that a dirty fast allows.

The rules of dirty fasting differ depending on the sources.

In the 2021 Nutrients study, researchers assigned 105 adults either water, a traditional breakfast, or a commercially available bar called Fast Bar (made from nuts, seeds, vegetable fiber and honey, with about 200 calories) after a 15-hour overnight fast.

The researchers found that the Fast Bar group had glucose levels comparable to that of the water-only group throughout the hours after the meal. Also, their ketone levels were similar to the water-only group two or more hours after the meal.

In contrast, the breakfast meal spiked glucose and reduced ketones. The Fast Bar eaters also experienced high self-rated levels of fullness and a decreased desire to eat compared to the water-only group.

Thus one Fast Bar consumed during the fasting window does not interfere with physiological fasting.

But without more research on how various foods, macronutrients, ingredients, and caloric intake impacts the body during dirty fasting, there are no science-backed rules about what you can eat during fasting hours.

Some say that any food or beverage during the fasting hours is okay, as long as it is less than 100 calories. Others only sanction high-fat foods, which do not immediately spike insulin, or allow higher-protein foods, like bone broth or collagen, during the fasting window.

In contrast, one 2021 study in the journal Nutrients pointed out that a lower protein intake is more effective at not triggering metabolic pathways in the body that sense the availability of nutrients.

Also, some may allow artificial sweeteners because they are zero calories. Still, a 2017 study in Physiology and Behavior showed that those sweeteners might increase insulin levels during a fast, even when tasted and not swallowed.

Many people interested in dirty fasting seek the health benefits of time-restricted eating but the flexibility to eat or drink something with caloric value during the fasting window. Flexibility helps them stay on track with their fasting routine because they are not as limited or as hungry.

But much more research is needed to understand the best way to practice dirty fasting and its possible benefits.

Nevertheless, regardless of what research does or does not say about the physiological effects of dirty fasting, there can be psychological or behavioral benefits.

For example, being able to nibble on something in the morning prevents over-splurging later in the day. And knowing what you can eat or drink helps you get through the tail end of a fasting window, even if you do not need the food or drink. 

But experts point out that the quality of what you eat during non-fasted hours (or the small dirty fasting windows) matters.

Nutrition is still the key. Be sure to build in a variety of vegetables, fruits and other whole foods daily to optimize the intake of vitamins, minerals, fiber, antioxidants and macronutrients.