Clean and Dirty Fasting

Clean vs Dirty Intermittent Fasting

No doubt you’ve heard of and possibly tried intermittent fasting. It has numerous scientifically proven benefits. But are you confused by terms like “clean” vs. “dirty” fasting? 

Clean and dirty fasting are terms that refer to what breaks a fast.  Some experts promote water-only intake during your fast while others claim that low-calorie drinks, stevia, MCT oil, and even a little bit of coffee creamer are okay.  

So, without further adieu, let’s take a deep dive deep into clean fasting vs. dry fasting, including the benefits, evidence, downsides, and takeaways. 

What is Clean Fasting?

Clean fasting is when you follow an intermittent fasting protocol and ingest only water or non-caloric beverages like tap water, mineral water, sparkling water, black coffee, and black tea. Sometimes, you’ll find information that says clean fasting must be calorie free. But beverages like black coffee still contain five calories per cup. However, that few calories are negligible. 

Water has no calories or sugar, and beverages like black coffee contain minimal amounts of calories, carbohydrates, fat, protein, and minerals. There are insufficient calories and carbohydrates to kick your body out of its fasted state, so it can continue its “metabolic switch” from burning carbs to burning fat as fuel. 

What Can You Consume During a Clean Fasting Window?

What Can You Consume During Clean Fasting

It’s essential that you stay hydrated during a clean fast. Have lots of water – sparkling, mineral or distilled are all good. However, if you are clean fasting, steer clear of additives like lemon slices, fruits, and herbs. They can add flavor to your water, but they eliminate the purpose of a “clean fast”.

Black coffee and tea are also allowed during a clean fast because they don’t trigger an insulin response in your body. However, research shows  black coffee may increase your insulin resistance to a small degree. 

Also, caffeine acts as a diuretic, which increases your urine production. In moderation, coffee probably won’t cause you to get dehydrated since it contains water, which will negate the diuretic effect. Studies show coffee can be as hydrating as water. However, that depends on how much you drink. If you drink more than 500mg of caffeine (about 4 cups of coffee) it can increase how much water you lose through urination. 

Moderate amounts of black coffee during a clean fast is totally safe, but if you’re concerned about hydration or insulin resistance, it may be a good idea to switch decaf black coffee, or choose herbal teas which are naturally caffeine-free, such as chamomile, or hibiscus. Plain old water can also do the trick!

What is Dirty Fasting?

Dirty fasting is when you eat foods or beverages that are under 50 calories during your fasting window. Your fasting is dirty if you add a bit of creamer to your coffee, or sip on tasty bone broth. Or maybe you add zero-calorie sweeteners in your tea, or drink zero-calorie soda. 

Do Artificial Sweeteners Raise Your Blood Sugar Levels? 

Aspartame is a common low-calorie artificial sweetener that is “allowed” in dirty fasts. The word “artificial” may raise some eyebrows, but aspartame doesn’t affect your insulin levels and blood glucose homeostasis, even if you’re diabetic. 

Similarly, research shows sucralose and Splenda, a zero-calorie sweetener, won’t trigger an insulin response. But, that doesn’t mean artificial sweeteners are good for you. They can increase your appetite (an extra challenge if you’re an intermittent faster), but Splenda and aspartame doesn’t seem to have this effect, which is why artificial sweeteners are such a popular substitute for table sugar. 

The research is mixed on whether artificial sweeteners cause issues overall, and they don’t seem to have any significant benefit. Long-term research is needed to see the impact of artificial sweeteners on your health. 

What Can You Consume During a Dirty Fasting Window?

What Can You Consume During Dirty Fasting

Here is a list of foods you can consume during a dirty fasting window. If you want to try dirty fasting, add them to beverages for flavour. 

  • 1 tbsp cream (30 calories, 0.5g carbs)
  • 1 tbsp 2% cow’s milk (18 calories, 1g of carbs) 
  • 2 tbsp almond milk (10 calories, 1g carbs)
  • 1 tsp honey (20 calories, 6g carbs)
  • 1 tbsp maple syrup (17 calories, 14g carbs) 
  • Stevia (0 calories, 0g carbs) and Splenda/sucralose (0 calories, 0g carbs)
  • 1 tbsp aspartame (35 calories, 7g carbs)
  • 1 tsp MCT oil (38 calories, 0g carbs) *100% fat
  • 1 cup bone broth (40 calories, 3g carbs)
  • Water + juice of 1 lemon (14 calories, 0g carbs)
  • Sugar-free chewing gum (0 calories, 0g carbs)

Can Dirty Fasting Be the Reason You’re Not Losing Weight?

There’s insufficient research to say whether 1 tbsp of honey or 2 tbsp of cream will kick your body out of a fasted state. If you are not seeing the results that you’d like, you may want to cut the bone broth or MCT oil and see if there are noticeable changes. Hopefully, there will be more research studies comparing dirty vs. dry fasts soon.

However, the reason for insufficient weight loss may be in your eating habits and food choices. Try to analyze your eating behavior closely to get a thorough picture.

Should You Go Clean or Dirty Fasting?

Depending on your goals, both types of fasting are fine. Ultimately, you should choose whatever way works best for you – this can be a matter of trial and error, personal choice, progress and goals! And don’t be afraid to combine the two techniques.

The flavors and fat in dirty fasts may give you the satiety and satisfaction you need to stick with fasting. So if you feel terrific, and love the taste of flavored water and coffee, go for it! However, if the taste is “negligible” for you, and you’re not seeing the results you want, it can be worth trying a clean fast. If you are not completely sure what fasting plan is right for you, take this quiz and find the fasting plan that will work best for you. Try it out for yourself and see what works best!

Author's bio


Trista Chan, RD, MHSc

Trista is a Registered Dietitian with her Master of Health Science in Nutrition Communication at Ryerson University, Toronto, and holds an Applied Human Nutrition degree and a graduate certificate in Workplace Wellness. Trista has diverse work experience in organizations both big and small. ...