Intermittent fasting has become a popular way to manage and lose weight and might have other health benefits, but what about dirty fasting? What is it and is it right for you? We asked registered dietitians for their thoughts.
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Fasting isn't a new or trendy concept. The practice of restricting food for a certain period of time has been around for centuries. Most commonly used for religious purposes or cultural beliefs, fasting has recently become a tool for weight-management with proponents also claiming its benefits on controlling blood sugar, calming inflammation and protecting brain health. Emerging from that trend is a take on intermittent fasting, known as dirty fasting, that may make fasting easier. But what exactly is dirty intermittent fasting and is it healthy?

What Is Dirty Fasting?

Before exploring dirty fasting, it's important to understand the concept of intermittent fasting. Intermittent fasting (IF) is a term used to describe the type of eating pattern where food is either partly or completely restricted during a certain period of time followed by a period of time where there is no restriction. Samantha Cassetty, M.S., RD, nutrition and wellness expert, and co-author of Sugar Shock says to "think of fasting as a different metabolic state, rather than just the absence of food or drinks. So, in this alternate metabolic state, your body does a better job clearing damaged cells, responding to stress, and suppressing inflammation."

There are different ways to go about this type of fasting. The first is time-restricted fasting where there is a designated time each day for eating. A popular version of this is the 16:8 method, where a 16-hour fast is followed by an 8-hour eating window. Modified fasting, also known as the 5:2 method involves eating normally for 5 days of the week and then limiting calories to 20-25% of energy needs for 2 consecutive days of the week. Alternate-day is another common form of fasting where fasting occurs every other day.

So what is a dirty fast? Think of it as the opposite of "clean fasting." Clean fasting implies fasting where none or very little food is consumed and only water and non-caloric beverages are allowed. Dirty fasting, on the other hand, is a form of modified fasting that allows the addition of a certain number of calories during the fast. How many calories break a fast? The amount of calories permitted (usually less than 100) and the types of food/drinks (typically high-fat that won't impact blood sugars) differ depending upon whom you ask. That's because the term "dirty fasting" has no common or agreed-upon definition and the research on it is extremely limited.

In short, there's no science that backs up the practice. Confirms Cassetty, "keep in mind that there are almost no studies on this form of fasting, and without evidence, we can't say whether this modified fasting protocol would produce similar benefits as might be experienced through other intermittent fasting protocols."

Sample Dirty Fasting Meal Plan

Here's what a day using the IF 16:8 method with dirty fasting might look like:

  • 10 am: 2 scrambled eggs, 1 piece sprouted whole grain toast and 1 grapefruit
  • 12 pm: 1 cup lentil soup, 1 cup spinach salad and 1 medium apple
  • 2 pm: 1 cup carrot sticks + ¼ cup hummus
  • 5 pm: Tofu and veggie stir-fry with 1 cup brown rice
  • 6 pm to 10am - FAST
  • 8 pm - 1 cup bone broth (40 calories)
  • 8 am - 1 cup tea with 1 tablespoon almond creamer (45 calories)

What are the Pros & Cons of Dirty Fasting?

Intermittent fasting may "improve insulin resistance, high blood pressure, and cognitive impairments," says Cassetty. It may also promote weight loss or prevent weight gain, although it may not do this better than another form of calorie reduction, she adds.

So what do you have to gain by dirty fasting? We're not entirely sure. Remember, there is very little research on dirty fasting, so we cannot say with any certainty that there are any health benefits, at least scientifically. However, based on the results of one study, adding a bit of food (a manufactured energy bar in this case) during the fasting period was found to help quell hunger during the fast. The approved bar used during the study "prolonged the physiological fasting state while also making it easier to fast," says Cassetty. Yet, she points out, this is one study, and it was funded by the company that made the bar used in it. It's also impossible to say whether eating something similar to this bar—for example, a similar macronutrient composition or a similar calorie level—would have the same effect.

Mascha Davis M.P.H., RDN, registered dietitian nutritionist, founder of sustainable seafood snack and author of Eat Your Vitamins says to think of dirty fasting as more of an extreme caloric reduction. She points out that caloric reduction can lead to weight loss, but this type of weight loss is often short term and unsustainable and in some cases, can be harmful. There is research, Davis says, that has shown that fasting can have negative effects on women's hormone levels and is not appropriate for certain other groups. Cassetty agrees there are risks and recommends that anyone with an eating disorder or anyone who has participated in any form of disordered eating, even if it's not a clinically diagnosed eating disorder, should avoid any form of intermittent fasting or dirty fasting. Also on that list, "pregnant and breastfeeding women, anyone with type 2 diabetes, anyone on any medication or anyone over 65 years old should avoid fasting unless their doctor gives them the green light."

Should You Try Dirty Fasting?

Without research, it's hard to recommend dirty fasting. As health professionals, we rely on science-backed evidence and there just isn't much here. That being said, if you'd like to try it, Davis recommends that you work with a credentialed expert, such as a registered dietitian. "Dietitians understand the science behind dieting and can make individualized recommendations that are tailored to you and your specific needs and goals."

Also, think beyond yourself says Cassetty. If you have kids, consider the type of behaviors you're modeling. "Are you normalizing body dissatisfaction or disordered eating? It's important to model a healthy relationship with food and your body, even if you aren't 100 percent happy with your body size or shape." And if improving your health is your main goal, Cassetty points out that there are other ways to promote longevity and healthy aging. "Both the Mediterranean Diet and Blue Zones Diet promote long, healthy lives while also focusing on the enjoyment of eating. So, depending on your needs and goals, one of these plans may be more suitable for you."