Fasting. I’m sure many of you have heard this word before. There are many claims out there about what fasting can do for one’s body. It’s been touted as a way to lose weight, a method to alter your gut microbiota, and even as a means to potentially extend your lifespan. And let’s not forget that fasting is also a significant part of many religious practices too. Fasting has been practiced globally for thousands of years and continues to dominate nutrition media today. But what does nutrition science say about fasting for gut health? As a gut health dietitian, I certainly get asked a TON about fasting.
The History of Fasting
Before diving into the research, let’s first explore where the word comes from. “Fasting” might seem like an odd term to describe the act of not eating. Shouldn’t it be something like “slowing or abstaining”? The word actually comes from the Old English fæstan, which means “to hold firmly”. This originally referred to abstaining from all food for religious or spiritual reasons. Fasting has a long history with religion. In Islam, Ramadan involves fasting from eating, drinking and smoking from sunrise to sunset for spiritual reasons. Today, fasting is practiced for a variety of reasons, other than just health, and countless variations of it have emerged over the past few decades. Let’s take a closer look at what modern research has to say about this ancient practice and its impact on gut health.
Important Considerations When Considering Fasting
It is important to note that fasting is the most extreme form of dietary restriction and typically eliminates all nutrients, except water. Certain populations are at higher risk when participating in fasting, such as:
- Those with eating disorders
- Individuals who are underweight or malnourished
- Those who engage in extreme exercise or work in physically demanding jobs
- Individuals with illnesses or chronic diseases
- Pregnant or breastfeeding women
- Children & adolescents
- Athletes
- Elderly people
These populations typically have specific nutrient needs, and fasting is not advised.
Food is more than just sustenance—it’s celebration, culture, religion, taste, connection, and nourishment. Fasting can sometimes distance people from these vital aspects of life. Therefore, before beginning any fasting regimen, always speak with your dietitian or a doctor to ensure you’re meeting nutritional needs, avoiding malnutrition, and determining whether fasting is the safest and most effective intervention to meet your health goals. Our bodies require nutrients to function, hug our loved ones, grow, and do all the things we love, so fasting must be approached with care.
As you will read, fasting can have both positive and negative impacts on certain gut conditions, so caution is necessary when implementing it. Many patients with gut conditions may find themselves unintentionally fasting due to a fear of how certain foods may worsen their symptoms. To learn how to manage gut conditions without fearing food, consult with a dietitian.
Types of Fasting
Not all fasting is created equally. There are several types of fasting used for different health outcomes. The most common types of fasting are:
- Time Restricted Feeding: This is when food intake is limited to certain windows, such as eating between 12 pm to 8 pm. The most common approach to time restricted feeding is a 16:8 pattern, where a 24 hour day is broken into a 16 hour fasting time and an 8 hour ‘eating window’.
- Alternate Day Fasting: In this type of fasting, one eats every other day. A common modified approach is the 5/2 method, where calories are restricted for 2 days and normal eating occurs for five days of the week. In this approach, it is not recommended to have the 2 calorie restricted days back to back.
- Modified Alternate Day Fasting: Similar to the previous type of fasting, but on fasting days, calorie intake is reduced to 15-25% of their energy needs. This biggest difference is that small amounts of food are consumed on fasting days.
- Prolonged Fasting: in this type, fasting lasts 4-7 days, and only water is consumed.
Fasting for Digestive Health Conditions
Did you know? The highest concentration of our immune cells is found within the gastrointestinal (GI) tract. These immune cells assist in controlling inflammation and protect the gut from parasites, pathogens, and viruses that we may ingest. However, when immune cells persist and increase in number without an actual ‘attack’ on the gut, we can see problematic inflammation that may contribute to gastrointestinal conditions like inflammatory bowel disease (IBD).
Inflammatory Bowel Disease (IBD)
IBD is characterized by inflammation of the gastrointestinal tract, leading to unfavorable symptoms such as changes in bowel movements, abdominal pain, structural changes to the intestine, nutrient deficiencies, and more. This disease can be divided into two types:
- Crohn’s Disease
- Ulcerative Colitis
The types of foods we eat can have either negative or positive impacts on inflammation. In particular, principles of the Mediterranean diet have been shown to reduce inflammation and maintain disease remission in individuals with IBD. This is one of the most evidence-based diets for those with IBD.
That being said, fasting is gaining traction as new approach that may help in managing inflammation and regulating the immune system. Here’s what we know so far:
- Animal studies suggest that intermittent fasting can reduce intestinal inflammation – however, we do need more high quality human studies to confirm this success.
- One case study in a female patient with ulcerative colitis found that inflammatory markers were significantly reduced after 8 weeks of time restricted feeding – however a single case is not a basis for making recommendations and there were some flaws in the study design.
- There have been a few studies conducted on IBD patients participating in Ramadan – with conflicting results.
- Both animal and clinical trials have demonstrated that intermittent fasting can assist with reduction in inflammatory markers (CRP and fecal calprotectin) in ulcerative colitis patients – there does not seem to be as much literature on the impact of fasting in Crohn’s disease.
The potential benefit of fasting for IBD is likely due to the reduction of foods that may contribute to inflammatory pathways. Reducing the intake of these foods can decrease inflammation. While this strategy could be effective, understanding which foods have positive effects on inflammation and nutrient status is the gold standard in nutritional guidance for IBD.
It is also important to recognize that malnutrition is very common in patients with inflammatory bowel disease. Therefore, fasting limits the opportunity to consume high quality nutrients and is certainly not ideal for every person with IBD.
Fasting and the Gut Microbiome
In addition to impacting inflammation, fasting has also been shown to cause changes in our microbiota. The gut microbiota consists of trillions of bacteria residing in our gut, which depend on the nutrients we provide to yield health benefits. A healthy microbiota is characterized by a rich diversity of bacterial strains and a substantial quantity of beneficial bacteria.
Although the research is still fairly limited in this area, some studies have shown that intermittent fasting leads to an increase in the presence of certain bacterial types that may help reduce the inflammatory response. However, other studies have seen no impact on bacterial diversity in fasting during Ramadan in healthy participants. Given these inconsistencies and the wide variability in study design, sample size, and population, there is still lots to learn! At this point, fasting does seem promising as a way to positively alter the gut microbiota. However, the exact mechanisms are still largely unknown.
Fasting for IBS
There is very little evidence about intermittent fasting and irritable bowel syndrome. One study from 2006 found that those who underwent fasting therapy saw improvements in abdominal pain, diarrhea, distention, and anxiety. However, the protocol used in this study is highly inapplicable to most people, as participants in the fasting group were put on a 10 day starvation followed by a 5 day ‘refeeding period’. I don’t know about you, but that doesn’t sound appropriate for most of the IBS clients I work with! It is highly restrictive and would require a lot of medical supervision to ensure things are done safely.
Additionally, when going extended periods without food, we often see that people get VERY hungry and end up overeating when their eating window finally arrives. Large volumes of food all at once could actually worsen IBS symptoms for some people. Those with diarrhea dominant IBS (IBS-D) tend to especially struggle with this, as eating large volumes can trigger the gastro-colic reflex, the message that tell the colon to “make room”, inducing the urge to rush to the washroom. Small frequent meals are generally recommended for those with IBS-D – and fasting makes that more difficult.
Similarly, fasting may not be ideal for those with gastroesophageal reflux disease (GERD). When they go from an empty stomach to eating a large amount of food in a short period, there is often a worsening of reflux. Therefore, fasting is not advised for these patients in most cases.
In Summary
There are various dietary approaches to managing gastrointestinal diseases. Fasting, alongside other dietary interventions, may play a role in improving disease outcomes. However, other approaches that may be more effective include working with a registered dietitian and identifying specific trigger foods instead of cutting out all foods for extended periods. Our bodies have specific nutrient needs regarding fat, protein, carbohydrate, vitamins, and minerals and we don’t want to become malnourished. While studies on fasting have shown some scientific evidence of assisting with gut conditions, the exact mechanisms are unknown. At this point, we don’t have enough research to support specific recommendations about type of fasting, duration of fasting, or specific disease states where fasting is beneficial. Ensuring proper nutrient status should always be the top priority.
Fasting appears to be safe for healthy individuals; however, it is not suitable for many vulnerable populations, such as children, elderly individuals, and pregnant people. It is recommended to seek guidance from a healthcare professional to ensure this is the most effective strategy for you.
Categorized: Feature, Gut Health & IBS
