Among various popular diet trends nowadays, such as the ketogenic diet, Whole30 diet, and Mediterranean diet, intermittent fasting has drawn considerable attention. And dirty fasting is a dietary method different from intermittent fasting.

Intermittent fasting refers to almost not eating or completely fasting during a specific period. For example, some people choose to fast for 24 hours every other day. On non-fasting days, their calorie intake can reach 125% of the average intake.

Time-restricted feeding is a common way of intermittent fasting, which means limiting the eating time within a day. The well-known 16:8 intermittent fasting diet method involves fasting for 16 hours and then eating within the remaining 8 hours. For instance, starting to fast at 8 p.m. until noon, and then eating from noon to 8 p.m.

Traditional fasting has strict requirements. During fasting, only zero-calorie or extremely low-calorie beverages such as water, black coffee, regular tea, and unsweetened herbal tea can be consumed. This kind of fasting is called "clean fasting".

From a scientific perspective, a 2021 study published in Frontiers in Endocrinology shows that the principle behind time-restricted diets is closely related to circadian rhythms. Our body's circadian rhythms are closely linked to metabolism, and mealtime is an important factor affecting metabolism.

Moreover, there is relevant evidence indicating that "clean fasting" can bring many benefits, such as helping to improve heart health, reducing blood pressure and blood sugar, and having a certain effect on weight loss. Additionally, some research has found that restricting the eating time from 7 a.m. to 3 p.m. within eight hours is relatively effective for weight loss and reducing body fat.

"Dirty fasting" can be regarded as another way of understanding and practicing time-restricted diets. It allows the intake of more calories or specific foods during the originally clean fasting period, with the goal of reaping benefits similar to "clean fasting" while minimally disrupting the concept of fasting.

Normally, fasting means not taking in any calories. However, with the emergence of time-restricted diets and the like, the meaning of fasting states at the physiological or molecular level has been redefined.

When we are in a fasting state, the amount of calories and carbohydrates our body takes in decreases, which leads to a drop in insulin levels, while the levels of glucagon and adrenaline hormones rise. Under their influence, fat cells release stored fat, part of which flows to the liver, where it is converted into ketone bodies and then released back into the bloodstream, becoming an energy source for the brain.

As long as the glucose and insulin levels in the body can be maintained at a relatively low level and the ketone body level remains relatively high, even if "dirty fasting" allows a certain calorie intake, it can still be considered a form of "fasting".

Regarding the rules of "dirty fasting", different people have different views.

Some websites that advocate "dirty fasting" believe that during the fasting period, as long as the calorie intake of food or beverage does not exceed 100 calories, anything can be eaten. However, there are other opinions. For example, only high-fat foods are allowed because such foods do not immediately stimulate insulin secretion.

Some people think that artificial sweeteners can be consumed since they contain no calories. However, a 2017 study in Physiology & Behavior shows that even just tasting a mouthful of artificial sweetener without swallowing it may increase insulin levels during fasting.

In addition, some followers of "dirty fasting" think that high-protein foods such as bone broth or collagen can be consumed during fasting. Nevertheless, a 2021 study in the Journal of Nutrition points out that a lower protein intake is more effective in avoiding triggering the metabolic pathways that sense the availability of nutrients in the body.

It should be noted that as of November 2022, due to a lack of sufficient relevant research, there is currently no scientific basis to support definite rules about what can be eaten during "dirty fasting". Most of the related suggestions on the market are only based on theory.

Many people interested in "dirty fasting" expect to obtain the health benefits of time-restricted diets on the one hand, and hope to be able to flexibly eat or drink something with calories during fasting on the other hand. They think this flexibility can help them better adhere to the fasting habit and not feel overly hungry due to excessive restrictions.

For example, many people have achieved prevention of overeating through time-restricted diets, making their eating schedules more regular and being more focused when eating. Even so, they still miss a cup of nut milk latte for breakfast, and "dirty fasting" may provide them with such flexibility to enjoy this drink.

Indeed, there is some evidence showing that "dirty fasting" has a certain effect. In a 2021 nutrition study, researchers asked 105 adults to take three different approaches after a 15-hour overnight fast: drinking water, eating a traditional breakfast, and eating a commercially available Fast Bar energy bar. It should be noted that I am a consultant of L-Nutra, and this company produces this energy bar and funded this study.

This Fast Bar energy bar is made of nuts, seeds, plant fiber, and honey, contains about 200 calories, has a relatively low protein content of 5 grams, is a low glycemic index food, has about six grams of net carbohydrates and 17 grams of fat.

After the participants ate each food, the researchers measured their blood sugar and ketone body levels every hour for four hours. The results showed that within a few hours after the meal, the blood sugar level of the Fast Bar group was similar to that of the group that only drank water; and two hours or more after the meal, the ketone body level of the Fast Bar group was also similar to that of the group that only drank water. In addition, those who ate the Fast Bar had a higher self-evaluated sense of satiety and a lower desire to eat.

From this research result, consuming a Fast Bar during fasting does not interfere with the physiological fasting state. Therefore, for those who follow intermittent fasting, they can use the Fast Bar to better carry out time-restricted diets.

However, this also raises some questions. For example, are other energy bars with similar compositions or equivalent food combinations also suitable for "dirty fasting"? Also, which foods or calorie intakes can maintain low blood sugar and high ketone levels during fasting?

In fact, so far, we still have a lot to learn about "dirty fasting". The theories about the effects of "dirty fasting" on health or weight loss that are circulating on the Internet are rarely supported by research. In short, more research is needed to figure out the best way to practice "dirty fasting" and its possible benefits.

Regardless of whether subsequent research can confirm the physiological effects of "dirty fasting", it may be beneficial in terms of psychology or behavior.

For example, eating something appropriate in the morning can prevent overeating later in the day. Or when you know what you can eat and drink during fasting, even if you don't actually need these foods or drinks, it can help you better get through the last stage of the fasting period.

Time-restricted diets may bring some additional health benefits besides helping with weight loss. However, experts also emphasize that the quality of diet during non-fasting or short fasting periods is very important.

Nutrition is always the key. We must consume a variety of vegetables, fruits, and other whole foods every day to optimize the body's intake of vitamins, minerals, fiber, antioxidants, and macronutrients.

Whether it is for weight management or the pursuit of physical health, the ultimate goal is to develop long-term sustainable good habits. Intermittent fasting or time-restricted diets essentially seek a balance between restriction and nutrition, rather than just focusing on restriction.

If you think "dirty fasting" is a relatively healthy compromise, then it may be the best choice for your lifestyle and your relationship with food.