Irritable bowel syndrome (IBS) is a very common condition of the gut which affects about 10% to 15% of the general population in the United States. Women are more likely to be affected than men.1,2
It is a chronic problem that affects the normal functioning of the gut. Typical symptoms that patients can present with are crampy abdominal pain, diarrhea, or constipation.
As IBS is a lifelong condition, it's not possible to completely cure the disease with medication alone.3 Patients need to try different treatment strategies, which often include dietary modifications.
People suffering from irritable bowel syndrome might find that their symptoms improve with certain types of foods, while other types might aggravate their condition.
Initially developed for the treatment of epilepsy, the keto diet has recently emerged as a popular way of eating among certain celebrities and lifestyle bloggers.4 It is a special type of low-carb, high-fat diet which can help with weight loss.
While it might be easy to dismiss the keto diet as another fad, there is emerging evidence for its numerous potential health benefits.5 So if you have IBS, you might be wondering if keto is good for you.
This article explores the potential benefits or side effects of the keto diet in patients with irritable bowel syndrome.
Irritable bowel syndrome can be divided into several subtypes depending on the predominant symptoms patients present with.
Patients can present either with IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), or mixed symptoms in which diarrhea and constipation alternate. Constipation refers either to passing hard, lumpy stools or having less frequent bowel movements. Constipation can last for days and can be very uncomfortable.6,7
Even though there hasn’t been any research that studied the effect of keto on IBS constipation, constipation is a frequently reported side effect of the keto diet.8 As the keto diet is low on carbohydrates, it means less fiber intake, which can affect gut motility.
People who first started the ketogenic diet might experience symptoms collectively called the "keto flu."9 The depletion of carbohydrates in the food intake forces the body into “ketosis” or fat breakdown which can result in a constellation of symptoms. These include headaches, fatigue, vomiting, difficulty sleeping, and constipation.
Constipation can worsen in individuals who primarily rely on animal-based fats and are not hydrated.10 Even though the symptoms of keto flu gradually improve over days, some people might experience side effects even after weeks.
People with irritable bowel syndrome are already sensitive to changes in their dietary patterns. There is evidence that a low-carb diet can improve symptoms in patients with diarrhea-predominant IBS.11
However, low carbohydrate and fiber intake are also known risk factors for constipation.12 Therefore, keto may not be suitable for patients with constipation dominant IBS (IBS-C). Drinking plenty of fluids and adding adequate fiber can help improve constipation.
Currently, there are no clinical guidelines that recommend keto for patients with IBS. There is no conclusive scientific evidence that would promote the use of the ketogenic diet as a primary treatment for these patients.
However, patients who have diarrhea-dominant symptoms (IBS-D) might benefit from a low-carbohydrate diet.
A study published in 2009 reported the beneficial effects of a low-carb diet in patients with IBS.11 17 patients that have been diagnosed with the condition were enrolled in this study. Patients were provided with a standard diet for the first 2 weeks, followed by very low-carb meals for 4 weeks.
13 patients completed this study, and the majority of them responded well to low-carb meals. 77% of participants reported significant improvements in their symptoms with associated improved quality of life.
So for patients with IBS with diarrhea, keto can be beneficial in providing symptomatic relief.
Previous research also suggests that IBS symptoms worsen with carbohydrate intake.13 This could be due to abnormal fermentation of carbs in the gut of these patients.
Therefore, the elimination of carbs can help alleviate the symptoms. The keto diet is primarily a low-carb diet, which means it can be suitable for patients with irritable bowel syndrome.
The ketogenic diet has a high-fat content which can worsen symptoms in some people. Several patients report a triggering of their symptoms with fat ingestion.14
This can be explained by some lab studies which suggest that the presence of fats in the gut can induce bloating. This effect is more exaggerated in people with irritable bowel syndrome, which can account for the triggering of symptoms.15,16
However, there is a lack of conclusive research that would accurately identify the relationship between fats and IBS.
There is now even evidence to suggest the contrary, that dietary fat might even have a positive effect.
IBS is linked with inflammation in the gut, and polyunsaturated fats might improve intestinal inflammation.17,18 More research is needed to study the effect of polyunsaturated fats on IBS.
Given the contradictory nature of available evidence, it might be worthwhile to assess the individual triggers of patient symptoms with fat intake. If patients experience worsening symptoms after dietary fat ingestion, it would be a good idea to curtail fat intake.
Normal human intestines contain bacteria that are generally harmless and might be beneficial for the body. For instance, a particular type of bacteria in the gut produces vitamin K.
However, in people with IBS, there might be an imbalance or overgrowth of these gut bacteria which could be contributing to the symptoms.19 Therefore, altering these bacteria in the gut can help improve symptoms in patients.
Recent research suggests that ketone bodies alter the bacterial flora in the gut. The mice model suggests that these altered levels of bacteria also help to reduce the TH17 immune cells in the gut.20 While these immune cells are critical in fighting off infections, the increased expression of immune cells contributes to autoimmune disorders. Autoimmune disorders result when the body's immune cells start attacking the body’s tissues. Even though IBS isn’t strictly classified as an autoimmune disease, there is a proposed link between it and immune system activation.21
As bacterial overgrowth in the gut is linked with IBS, the reduction in the number of harmful gut bacteria can help improve symptoms in patients. The effect of the ketogenic diet in altering gut bacteria has also been observed in human studies.22
Patients with irritable bowel syndrome report a worsening of their symptoms after carbohydrate intake. Therefore, researchers attribute their symptoms to the malabsorption of carbohydrates in the gut.23
According to the carbohydrate malabsorption theory, the fermentable oligosaccharides, disaccharides, and monosaccharides trigger inflammation in the distal small intestine and colon in patients with IBS. Moreover, the fermentation of carbs in the gut produces abdominal "gas" and distension which can be uncomfortable for patients.24,25
Another theory suggests the possible role of fructose intolerance.26 Patients with IBS might experience abdominal pain, cramping, and flatus with fructose intake.
In addition, removal or limited carbohydrate intake improves symptoms in these patients. This is the reason why individuals with IBS are generally recommended to follow a special form of diet called the "low-FODMAP" which limits the intake of fermentable carbs.27
Both keto and low-FODMAP greatly reduce the amount of carbohydrates in the diet. Therefore, there might be an overlap between these two dietary patterns. As a ketogenic diet restricts carbohydrate intake, the majority of carbohydrates that would be classified as low-FODMAP would be eliminated as well.
However, keep in mind that certain foods are low-carb but not compatible with a low-FODMAP diet. One such vegetable is cauliflower, which is regarded as the "vegetable of choice" for keto.28 However, it's regarded as a high-FODMAP food and wouldn't be suitable for someone with IBS.
In short, no. The ketogenic diet is distinct from the low-FODMAP plan. While both diets restrict carbohydrates, certain foods allowed in keto are not compatible with the low-FODMAP, and vice versa.
Dairy products that are allowed in ketogenic diet plans can be triggering for people with IBS. Another example of a keto food that would be incompatible with the low FODMAP is cauliflower. Cauliflower contains high polyol content and even though it is low carb, it is not suitable for people with IBS. Some other examples of high-FODMAP vegetables include Brussels sprout, asparagus, mushrooms, leek, and snow peas.29-31
Unlike keto, low-FODMAP was primarily developed for patients with irritable bowel syndrome and eliminates fermentable carbohydrates from dietary intake. In addition, instead of being a lifestyle choice, low-FODMAP is a 3-phase plan. It involves the restriction of all high-FODMAP food items for a limited period with the gradual reintroduction of certain FODMAP to assess the patient's sensitivity to that particular food item. Patients are allowed more freedom with their dietary intake over time.32
It should be noted that improperly following the low-FODMAP diet can result in deficiencies of important nutrients. Moreover, the reintroduction phase is critical. Each food group is introduced for 3 days and in the absence of symptoms, the next food group is introduced after 1 day. This requires expert monitoring and guidance.
Therefore low-FODMAP should only be followed under the direct supervision and guidance of a registered dietitian. You can also speak with them about the possibility of combining keto and low-FODMAP.
Research on the ketogenic diet and IBS is limited and available evidence is contradictory. Therefore, there is no conclusive evidence that would establish the routine use of keto in IBS patients.
On one hand, some patients experience improvement in their symptoms, while there is also a potential for aggravation of symptoms in susceptible individuals.
If you have IBS and wish to start a keto diet, it is best to consult your medical practitioner and a registered dietitian. They would be able to assess your triggers and decide if a ketogenic diet is suitable for you.
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