When starting a ketogenic diet, many dieters experience uncomfortable digestive symptoms such as bloating.
These symptoms are often the result of the keto flu, but some may also be due to poor dietary habits.
Below, I explain what exactly may be causing bloating on a ketogenic diet and offer a couple of solutions based on current research.
What is keto bloating?
Keto bloating is a type of bloating that you experience upon initiating a ketogenic (keto) diet.
This symptom is fairly common among keto beginners and long-term dieters. Luckily, for the most part, it is not a sign of anything serious.
However, if left untreated, keto bloating can slow down weight loss and make sticking to the keto diet difficult.
To help you understand why you need to treat keto bloating, let me start by explaining what bloating actually is.
Bloating is a condition where the abdomen feels full and tight and may even look distended . Bloating can be temporary or chronic.
Common causes of bloating include: 
• Swallowing air
• Acid reflux (GERD)
• Irritable bowel syndrome (IBS)
• Lactose intolerance
• Microbial imbalances
Researchers are still looking for an explanation for why these conditions lead to bloating.  Because we know little about the mechanisms behind bloating, finding a treatment has remained a challenge.
With that in mind, finding what will work for your keto bloating will involve plenty of trial and error.
But getting to an effective solution becomes much easier when you focus on the most common causes of keto bloating.
And while general bloating causes are innumerable, here are the most common ones related to a ketogenic diet.
Reason #1. You are running low on fiber
Dietary fiber refers to indigestible carbohydrates like cellulose, resistant starch, inulin, beta-glucans, polysaccharides, and oligosaccharides.
There are two types of dietary fiber: soluble and insoluble. However, both are important if your goal is to avoid constipation and bloating.
Soluble fiber forms a gel-like consistency when mixed with fluids.
This characteristic helps this fiber make the stool softer and easier to pass. Insoluble fiber gives stool bulk, which speeds up passage time.
Meeting your daily fiber needs becomes challenging on keto because this diet demands lower overall carbohydrate intake (fiber is a type of carbohydrate).
The recommended daily intake for fiber is around 30g per day. To meet this requirement, increase your intake of low-carb, high-fiber foods like:
- Almonds (3.5g per oz)
- Peanuts (4.6g per oz)
- Blackberries (3.5g per ½ cup)
- Artichokes (10.3g per one medium)
- Sauerkraut (3.4g per ½ cup)
- Avocado (9.8g per 1 cup)
Optionally, you can add fiber supplements to boost your daily intake. The best fiber supplement for constipation relief is psyllium husk, a non-fermentable fiber that research shows are effective. 
Because psyllium does not ferment in your colon, it is also less likely to cause gas and bloating.
Besides boosting fiber intake, it is important that you also drink enough fluids.
Women should drink around 11 cups and men around 15 cups of fluids a day to help fiber dissolve in the digestive tract.
Keep in mind that fluid meals like soup and smoothies also account for your daily fluid intake.
Reason #2. You cheated and carbed up
Carbohydrates can be quite addictive . Their effects on the central nervous system are powerful enough to make eating more than you planned.
But the biggest problem with overeating on carbs when you've been on a keto diet is that, not only will it kick you out of ketosis, it will also leave you feeling bloated.
The reason carbing up on keto causes bloating has most likely to do with adaptability. It takes time for your body to adapt to keto, and it takes just as much for it to revert back to fueling on carbohydrates. Below, I explain why this is so.
Research has long ago discovered that pancreatic and intestinal enzymes change in response to macronutrient intake . In other words, the levels of carbohydrate-digesting enzymes, like amylase and maltase, drop in response to low-carb diets.
Without enough enzymes to digest carbohydrates, more reach the colon to be fermented, leading to excess gas production and bloating. So, what you are experiencing is, in fact, temporary carb intolerance .
Another problem with carbups is fluid retention. Many people falsely refer to this as bloating . However, fluid retention is a completely different condition to bloating and is often referred to as edema.
Edema is characterized by swelling and puffiness in the face and extremities. When mild, edema is not a sign of anything serious and is, in fact, quite common, especially following carbups.
The reason carbs can cause edema is because they increase sodium and water absorption . When converted to muscle glycogen, carbohydrates also increase glycogen levels in your muscles (glycogen is four parts water) .
Because low-carb diets deplete muscle glycogen, you lose water. Conversely, refeeding on carbohydrates increases fluid retention.
To treat carbup bloating, there are two things you can do: cut back on carbs and take electrolytes.
Reducing carbohydrates will quickly put you back into ketosis. Once you are in ketosis, you will lose any excess water weight within the first week and experience less bloating.
To minimize keto flu symptoms while you are getting back into ketosis, make sure to take enough electrolytes and consume the recommended amount of fat.
Reason #3. You have a food sensitivity
When switching to a low-carb diet, chances are you will start eating a plethora of new foods.
While this can be a positive thing in terms of nutrient intake, the downside is that you may end up introducing food for which you have an undiagnosed food sensitivity.
Food sensitivities are also called food intolerances. They often result from a lack of digestive enzymes or hypersensitivity to certain compounds. 
However, some food intolerances are mediated by the immune system – these are referred to as food allergies. A very common food intolerance, for example, is lactose intolerance.
Besides bloating, other symptoms of a food sensitivities include migraines, headaches, abdominal pain, flatulence, and diarrhea.
If you are experiencing any of these, ask your doctor to perform a food allergy test to rule out this problem. If the tests come out negative, then you will want to carry out an at-home food sensitivity test:
Testing for food sensitivities
Because there are no tests for food intolerances, the only way to test if you have one is by monitoring your symptoms after eating a particular food.
You may also want to try cutting out suspected foods and reintroducing them to see if there's any difference. This is called an "elimination diet" and is quite effective in tracking down food intolerances.
Some foods are more likely to cause food sensitivities than others. Try following an elimination diet by excluding these foods:
- Artificial sweetener
Some food sensitivities also result from an inability to digest simple carbohydrates and sugar alcohols. These nutrients are collectively referred to as FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols).
FODMAPs are believed to be behind irritable bowel syndrome (IBS) – a common cause of bloating even among keto dieters. 
Foods highest in FODMAPs include:
- Coconut water
Keep in mind that the complete list of FODMAP food is quite a long one. You may find several versions of it online.
A major downside to following a low-FODMAP diet is that you run the risk of not eating enough fiber.
Reason #4. You are overeating on foods that promote bloating
Sometimes, the actual cause of keto bloating happens to be the simplest one: overeating on foods that causes bloating. Even if you don't suffer food sensitivities or a digestive disorder, these foods will lead to bloating.
The most common offenders include:
Dairy contains lactose, a milk sugar that most people have trouble digesting because they lack the lactase enzyme. Around 70% of the world's population suffers some degree of lactose intolerance due to a genetically programmed decline in lactase production after weaning .
However, you do not have to exclude all dairy on your low-carb diet if you suspect lactose intolerance. High-fat dairy is generally lower in lactose than low-fat dairy. Fermented and aged dairy like yogurt, sour cream, kefir, and hard cheeses are also lower in lactose. Butter, being mostly milk fat, has the least lactose of all dairy products.
Brussels sprouts, broccoli, cauliflower, and kale are all examples of vegetables belonging to the Brassica family. These vegetables contain raffinose, a complex sugar that many people are unable to digest properly and that studies linked to bloating and flatulence .
These vegetables also contain sulfur, a chemical element with an unpleasant odor and that causes foul-smelling flatus . Other sulfur-containing foods include eggs, cheddar, organ meats, grass-fed dairy. While sulfur may not necessarily make you bloated, it can lead to unpleasant flatus.
Club soda and carbonated water are allowed on low-carb diets. They make for a refreshing drink, but that often causes bloating. These drinks contain a gas called carbon dioxide that can accumulate in your GI tract. In fact, limiting your intake of carbonated beverages is one of the most common recommendations for reducing bloating .
On a low-carb diet, most people substitute sugar with artificial sweeteners like sorbitol and other sugar alcohols. Sugar alcohols are not digested and tend to ferment in the colon, which can cause bloating . However, the same holds true for natural sweeteners like stevia and monk fruit.
Try eliminating some or all of these foods if you believe they cause intolerable bloating. Optionally, you can simply try to reduce your intake to see if that makes a difference. This should be especially the case with artificial sweeteners, which can be particularly hard on your digestive tract.
Reason #5. You are going heavy on the MCT’s
Medium-chain triglycerides (MCTs) are a valuable tool on a keto diet that can speed up ketosis. Many keto dieters get their MCTs from pure MCT oil, which contains up to 100% of these fats. However, coconut and palm kernel oils also contain MCTs but to a smaller extent.
Unfortunately, MCTs do cause digestive upset when taken in excess. Studies on MCT oil have reported side effects like diarrhea, bloating, vomiting, and cramps .
MCTs are a concentrated source of fats that are otherwise difficult to obtain from food. The only known sources of MCTs are coconut oil, palm kernel oil, and dairy. Your body is likely not used to MCTs, so it is important to keep intake within a moderate 60-100ml per day limit.
I suggest starting with a minimum MCT dosage and building on from there. Most dieters are able to build tolerance with a gradual increase in dosage.
At moderate levels, these fats may even improve your GI health and lead to less bloating. That's because they also have anti-inflammatory properties and are easier to absorb than other fatty acids.
Reason #6. Leaky gut syndrome
Leaky gut is also known as "increased intestinal permeability." What that means is that the intestinal barrier is not filtering properly, which leads to bacteria and toxins entering the circulatory system and causing an immune reaction that leads to low-grade inflammation.
Leaky gut usually results from conditions such as inflammatory bowel diseases, celiac disease, food allergy, irritable bowel syndrome, obesity, and metabolic diseases. However, researchers also claim that leaky gut can result from changes in gut flora caused by a high-fat diet. 
Healthy gut bacteria produce butyrate, a short-chain fatty acid important for reducing inflammation in the colon. Their imbalance on keto can decrease butyrate production.
Symptoms of leaky gut include fatigue, digestive upset, bloating, and fatigue. Keep in mind that leaky gut is not yet a recognized medical diagnosis, but increased intestinal permeability definitely is.
If you suspect that leaky gut may be behind your bloating on a low-carb diet, then there are steps you could take:
The keto diet can disrupt your intestinal flora, especially if you do not eat enough fiber. Try improving your gut microbial balance with probiotic foods like yogurt, kefir, sauerkraut, and kimchi, and balance this with your fiber intake.
Consider anti-inflammatory food
Foods high in antioxidants and phytochemicals are anti-inflammatory. Examples include turmeric, ginger, berries, and olive oil. Of these, studies found turmeric to be especially beneficial for gut health.
Other anti-inflammatory foods include those rich in omega-3 fatty acids. These fatty acids are also anti-inflammatory in nature. Unfortunately, most people these days do not get enough omega-3s from their diet, which might explain the global rise in chronic illness. Great sources of high-quality omega-3s include fatty fish, fish oil, and algae. Other good sources are walnuts and flaxseed.
Increase your fiber intake
Helpful gut bacteria feed on dietary fiber. Without enough fiber, these bacteria are unlikely to thrive and, instead, opportunistic bacteria start to take over. If you do not suffer from any carb intolerance, then do add fiber to your low-carb diet.