Clean vs. Dirty Fasting – Which Is More Effective?

Because of the many scientifically proven benefits, you’ve probably heard of intermittent fasting and perhaps even tried it. New approaches and terms such as “clean and dirty fasting” continue to evolve as with other diets.

Therefore, this article differentiates clean and dirty intermittent fasting by addressing proven benefits and drawbacks and concludes if the dirty approach can be effective.

Clean and dirty fasting refers to whether a drink or food breaks the fast. 

Opinion on intermittent fasting is often not unanimous.

While some experts recommend drinking only water during the fast, others claim that low-calorie drinks, sweeteners, cream, or Bulletproof Coffee are fine.

We need to delve deeper into the terminology to help us understand the difference between clean and dirty intermittent fasting based on science.

Contents: Intermittent Fasting | Clean | Dirty | Effectiveness | Which Is Better

What Is Intermittent Fasting?

Intermittent fasting involves eating during a specific period and fasting the rest of the day.

Although there are several forms of intermittent fasting, the most popular is fasting within a 16-hour window.

Therefore, in the classic 16/8 intermittent fasting, you may eat only during a window of 8 hours per day, for example, from 12:00 to 20:00.

Clean and dirty fasting refers to your consumption during the 16-hour fasting window.

What Is Clean Fasting?

Clean means you don’t consume calories during the 16 hours of fasting.

Therefore, you are essentially limited to three beverages:

• Water or mineral water
• Unsweetened tea 
• Black coffee

However, drinks like green tea or black coffee still contain about 2.5 calories per cup. Nonetheless, most experts agree that this amount is negligible and does not interrupt fat-burning (ketosis).

In addition to ketosis, a second mechanism is responsible for the lion’s share of fasting’s health benefits – autophagy (Levine et al. 2017¹). 

The following nutrient sensors in the body can turn this recycling system in our cells off:

• Insulin: Sensitive to carbohydrates and proteins
• mTOR: Sensitive to proteins 
• AMPK: Sensitive to lack of energy in cells

Since AMPK can also be affected by fat, the simplistic approach was born: any caloric food breaks the fast.

We will see that this approach is incorrect when we look at the disadvantages of dirty intermittent fasting. That is why, for example, in clean fasting, non-nutritive sweeteners such as stevia are not allowed.

Moreover, there still exists an increase of clean fasting – autophagy fasting. Proponents of pure autophagy fasting consume only water and sometimes natural salt such as pink Himalayan salt.

However, this is not as much an intermittent or therapeutic fasting method. Therefore, salt is allowed as well. Because the body loses sodium over several days of fasting, this can cause dizziness and headaches.

What Is Dirty Fasting?

Dirty or lazy intermittent fasting is a new term that allows food intake of up to 100 calories during fasting.

For example, dirty intermittent fasting allows the following foods and sweeteners (in beverages) during the 16 hours:

• 2 tbsp. cream: 30 calories / 0.8 g carbohydrate / 0.6 g protein / 11.0 g fat (*)
• 2 tbsp. whole milk: 18.3 calories / 1.6 g carbohydrates / 1.0 g protein / 1.0 g fat (*)
• 2 tbsp. almond milk: 5 calories / 0.2 g carbohydrates / 0.1 g protein / 0.4 g fat (*)
• 14 grams of grass-fed butter: 100 calories / 0.0 g carbohydrates / 0.0 g protein / 11.4 g fat (*)
• 2 tsp. MCT oil: 84 calories / 0.0 g carbohydrates / 0.0 g protein / 10 g fat (*)
• 1 cup bone broth: 100 calories / 1.5 g carbohydrates / 0.9 g protein / 0.4 g fat (*)
• 1 lemon (juice squeezed): 11.7 calories / 4.1 g carbohydrates / 0.2 g protein / 0.0 g fat (*)
• 1 can coke zero: 0.0 calories / 0.0 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 pack splenda (sucralose): 3.4 calories / 0.9 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 pack stevia (pure): 0.0 calories / 0.0 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 tbsp. agave syrup: 60 calories / 21.3 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 tbsp. honey: 64 calories / 17.3 g carbohydrates / 0.1 g protein / 0.0 g fat (*)
• 1 sugar-free chewing gum: 5.4 calories / 1.9 g carbohydrates / 0.0 g protein / 0.0 g fat (*)

In summary, dirty intermittent fasting allows diet drinks, sweeteners, and other additions to tea and coffee, while not exceeding 100 calories.

Diet sodas, low-calorie sweeteners, and some food – sounds like a relaxed version of intermittent fasting.

Can this dirty, lazy intermittent fasting be similarly effective as the clean one?

Is Dirty Fasting Effective?

Dirty fasting has only one rule, which limits energy intake to 100 calories during fasting. But that’s where the problem lies.

Technically, any macronutrient breaks the fast in terms of autophagy. 

However, experts overwhelmingly agree that minimal amounts, such as in green tea, cannot significantly interfere with autophagy.

Nevertheless, consuming 100 calories will reduce autophagy to an absolute baseline level. Hence, this calorie intake eliminates most rejuvenating effects of fasting.

But the three macronutrients cannot be lumped together when it comes to weight loss since the storage hormone insulin regulates our body weight.

For example, researchers can predict up to 75% of the gain and loss of overweight people based on insulin levels (Kong et al. 2013²).

Since insulin blocks the enzyme that breaks down body fat, a low insulin level is a prerequisite for losing weight (Meijssen et al. 2001³).

While pure fat such as butter does not elevate insulin, a tablespoon of honey spikes blood glucose and insulin levels.

Similarly, protein without the protective effect of fat can stimulate insulin secretion. Thus, protein powder in coffee, for example, is not a good idea (Nuttall et al. 1991⁴).

Although many nutritionists reduce foods to their effects on blood glucose, this approach is doomed to failure.

It ignores that it is not only blood glucose that can cause an insulin response. 

For example, the following zero-calorie sweeteners can also stimulate insulin secretion (Anton et al. 2010⁵; Liang et al. 1987⁶; Pepino et al. 2013⁷; Jeppesen et al. 2000⁸; Zhou et al. 2009⁹):

• Acesulfame-K (zero drinks)
• Aspartame (diet soda)
• Sucralose (Splenda)
• Stevia
• Monk fruit

Since dirty fasting completely ignores the insulin perspective, it breaks fasting and ketosis. Therefore, it cannot be as effective as clean intermittent fasting.

Clean vs. Dirty Fasting

In contrast to clean intermittent fasting, the disadvantages outweigh the advantages of dirty fasting. Especially since dirty intermittent fasting only relates to calories and not insulin levels, it is not nearly as effective for weight loss.

However, if we modify the essential rule to include insulin in our considerations, dirty fasting can work.

In this case, the allowed calorie intake during fasting is limited to pure fat, which does not stimulate insulin secretion.

As a result, we get so-called fat fasting. For example, this legitimizes the ever-popular Bulletproof Coffee since only butter, ghee, coconut, or MCT oil are in it.

Due to consistently low insulin levels, many people achieve excellent weight loss results despite consuming coffee or tea drinks with pure fat.

In addition, fatty drinks help to satiate beginners to last longer when fasting.

For this reason, combining a ketogenic diet and intermittent fasting is most effective for weight loss.

The Takeaway

The dirty intermittent fasting approach is not effective because it restricts foods to calorie values.

If you still have trouble fasting for an extended time, I suggest a dirty fat fasting approach that evaluates foods based on insulin response.

Given our examples of beverage additions, this results in a yes and no list for effective dirty fasting.

Accordingly, the following foods are allowed in dirty fat fasting:

• 2 tbsp. cream: 30 calories / 0.8 g carbohydrate / 0.6 g protein / 11.0 g fat (*)
• 14 grams of grass-fed butter: 100 calories / 0.0 g carbohydrates / 0.0 g protein / 11.4 g fat (*)
• 2 tsp. MCT oil: 84 calories / 0.0 g carbohydrates / 0.0 g protein / 10 g fat (*)
• 1 cup bone broth: 100 calories / 1.5 g carbohydrate / 0.9 g protein / 0.4 g fat (*)

Although fat interferes with autophagy, it does not stop fat burning.

In contrast, the following foods will affect your weight loss success:

• 2 tbsp. whole milk: 18.3 calories / 1.6 g carbohydrates / 1.0 g protein / 1.0 g fat (*)
• 1 can coke zero: 0.0 calories / 0.0 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 pack splenda (sucralose): 3.4 calories / 0.9 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 pack stevia (pure): 0.0 calories / 0.0 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 tbsp. agave syrup: 60 calories / 21.3 g carbohydrates / 0.0 g protein / 0.0 g fat (*)
• 1 tbsp. honey: 64 calories / 17.3 g carbohydrates / 0.1 g protein / 0.0 g fat (*)

In addition, non-nutritive sweeteners fuel cravings, according to science (Yang 2010¹⁰).

Frequently Asked Questions (FAQ)

Why Intermittent Fasting is bad?

According to countless studies, intermittent fasting is not harmful at all. It offers various health benefits, helps to lose weight, and even reverses type 2 diabetes.

How many calories can you have while dirty fasting?

Dirty fasting allows 100 calories during the fasting period. But depending on what you eat, it may nullify weight loss results.

Does coffee break intermittent fasting?

While black coffee without sweeteners does not break a fast, coffee with milk or any zero-calorie sweetener will.

Do you have to eat clean while intermittent fasting?

It depends on how you define clean eating in the context of intermittent fasting. You should not eat during the fasting period. You will get the best results if you eat low-carb or keto during the eating window.

Studies

#1-6

¹ Levine B, Klionsky DJ. Autophagy wins the 2016 Nobel Prize in Physiology or Medicine: Breakthroughs in baker’s yeast fuel advances in biomedical research. Proc Natl Acad Sci U S A. 2017 Jan 10;114(2):201-205. doi: 10.1073/pnas.1619876114. Epub 2016 Dec 30. PubMed PMID: 28039434; PubMed Central PMCID: PMC5240711. 

² Kong LC, Wuillemin PH, Bastard JP, Sokolovska N, Gougis S, Fellahi S, Darakhshan F, Bonnefont-Rousselot D, Bittar R, Doré J, Zucker JD, Clément K, Rizkalla S. Insulin resistance and inflammation predict kinetic body weight changes in response to dietary weight loss and maintenance in overweight and obese subjects by using a Bayesian network approach. Am J Clin Nutr. 2013 Dec;98(6):1385-94. doi: 10.3945/ajcn.113.058099. Epub 2013 Oct 30. PubMed PMID: 24172304.  

³ Meijssen S, Cabezas MC, Ballieux CG, Derksen RJ, Bilecen S, Erkelens DW. Insulin mediated inhibition of hormone sensitive lipase activity in vivo in relation to endogenous catecholamines in healthy subjects. J Clin Endocrinol Metab. 2001 Sep;86(9):4193-7. doi: 10.1210/jcem.86.9.7794. PubMed PMID: 11549649. 

⁴ Nuttall FQ, Gannon MC. Plasma glucose and insulin response to macronutrients in nondiabetic and NIDDM subjects. Diabetes Care. 1991 Sep;14(9):824-38. doi: 10.2337/diacare.14.9.824. Review. PubMed PMID: 1959475. 

⁵ Anton SD, Martin CK, Han H, Coulon S, Cefalu WT, Geiselman P, Williamson DA. Effects of stevia, aspartame, and sucrose on food intake, satiety, and postprandial glucose and insulin levels. Appetite. 2010 Aug;55(1):37-43. doi: 10.1016/j.appet.2010.03.009. Epub 2010 Mar 18. PubMed PMID: 20303371; PubMed Central PMCID: PMC2900484. 

⁶ Liang Y, Steinbach G, Maier V, Pfeiffer EF. The effect of artificial sweetener on insulin secretion. 1. The effect of acesulfame K on insulin secretion in the rat (studies in vivo). Horm Metab Res. 1987 Jun;19(6):233-8. doi: 10.1055/s-2007-1011788. PubMed PMID: 2887500. 

#7-10

⁷ Pepino MY, Tiemann CD, Patterson BW, Wice BM, Klein S. Sucralose affects glycemic and hormonal responses to an oral glucose load. Diabetes Care. 2013 Sep;36(9):2530-5. doi: 10.2337/dc12-2221. Epub 2013 Apr 30. PubMed PMID: 23633524; PubMed Central PMCID: PMC3747933. 

⁸ Jeppesen PB, Gregersen S, Poulsen CR, Hermansen K. Stevioside acts directly on pancreatic beta cells to secrete insulin: actions independent of cyclic adenosine monophosphate and adenosine triphosphate-sensitive K+-channel activity. Metabolism. 2000 Feb;49(2):208-14. doi: 10.1016/s0026-0495(00)91325-8. PubMed PMID: 10690946.   

⁹ Zhou Y, Zheng Y, Ebersole J, Huang CF. Insulin secretion stimulating effects of mogroside V and fruit extract of luo han kuo (Siraitia grosvenori Swingle) fruit extract.. Yao Xue Xue Bao. 2009 Nov;44(11):1252-7. PubMed PMID: 21351724.   

¹⁰ Yang Q. Gain weight by “going diet?” Artificial sweeteners and the neurobiology of sugar cravings: Neuroscience 2010. Yale J Biol Med. 2010 Jun;83(2):101-8. PMID: 20589192; PMCID: PMC2892765.