Many people who start a ketogenic diet notice changes in their bowel habits. However, it’s important to recognize that this doesn’t always mean they have true constipation. On a keto or low-carb diet, food volume often decreases, which can lead to smaller or less frequent bowel movements. This can be completely normal.
Constipation is typically defined as:
- Fewer than three bowel movements per week
- Hard, dry, or difficult-to-pass stools
- A feeling of incomplete evacuation
If you’re simply going less often but feel comfortable and are passing stools easily, this may reflect normal adaptation rather than a problem.
However, if you are experiencing true constipation, several factors related to a ketogenic diet may contribute.
Consuming Too Much or Too Little Fiber
Lack of fiber is often assumed to be the main cause of constipation. While this can be true in some cases, fiber needs vary widely from person to person.
Too little fiber may reduce stool bulk and slow intestinal transit. However, increasing fiber isn’t always the answer. Consuming too much – especially if increased quickly – can lead to bloating and may worsen constipation, particularly when fluid intake is low. In addition, some types of fiber can be more binding and not well tolerated in larger amounts.
While some people may achieve bowel regularity by eating a few servings of high-fiber vegetables per day, others may do better with less. Because of this, it’s often more effective to pay attention to your individual response rather than assuming that more fiber is better.
Changes in the Gut Microbiome
On a ketogenic diet, the composition of the gut microbiome – the bacteria that live in the digestive tract – may change. In some individuals, a lower intake of fermented foods containing beneficial bacteria may also affect digestive function. Together, these changes may contribute to constipation, particularly during keto adaptation.
Not Enough Sodium
Sodium plays a key role in maintaining fluid balance. When intake is too low, more water is reabsorbed in the colon, and stools can become drier and harder to pass.
This is one of the most common – and often overlooked – causes of constipation in people following a ketogenic lifestyle.
Dehydration
Fluid needs often increase on a ketogenic diet due to increased sodium loss. As insulin levels drop in response to very low carb intake, the kidneys excrete more sodium and water, which can reduce fluid availability in the digestive tract.
Even mild dehydration can lead to harder, drier stools that are more difficult to pass. This is a common and often overlooked contributor to constipation on a ketogenic or low-carbohydrate diet.
As mentioned above, sodium is essential for maintaining fluid balance. Without adequate sodium, the body may not retain enough fluid to support normal bowel function. For this reason, hydration is most effective when paired with adequate sodium intake.
Not Consuming Enough Fat
Dietary fat stimulates the release of bile, which helps support intestinal motility. If fat intake is too low, bile flow may be reduced, and movement through the digestive tract can become slow.
Including enough fat can help promote more regular bowel movements. Plus, fat provides most of your energy needs on a keto diet. Healthy fat sources include olive oil, avocados, butter, and fatty fish.
Inadequate Magnesium Intake
Magnesium plays an important role in muscle relaxation, including the smooth muscle of the intestines, and helps draw water into the bowel. Both of these effects support normal intestinal motility and stool consistency.
Low magnesium intake may contribute to constipation, and this may be particularly true on a ketogenic diet, where intake of magnesium-rich foods may decrease.
Ensuring adequate magnesium, through food or supplementation, can help support more regular bowel movements and overall digestive function.
Not Moving Enough
Physical activity helps stimulate intestinal motility, which is the movement of food and waste through the digestive tract. When activity levels are low, intestinal transit may slow, contributing to constipation.
Regular movement has been shown to significantly reduce the risk of constipation. Even light activity, such as walking, can help promote normal digestive function and improve regularity.
Practical Strategies to Improve Constipation on Keto
If constipation is an issue, consider the following:
- Increase sodium intake by drinking 1-2 cups of broth daily, salting food liberally, or consuming keto-friendly foods high in salt like olives and pickles.*
- Stay well hydrated, especially during the adaptation phase. This often means consuming 2.5 to 3 liters of water (or more) per day.
- Ensure adequate fat and protein intake to meet your needs. Use the MyMojoMacros Calculator to determine your targets.
- Adjust fiber intake by increasing or decreasing your intake, depending on tolerance. Learn more by reading Fiber on a Ketogenic Lifestyle.
- Include low-carb fermented foods, such as sauerkraut, apple cider vinegar, kimchi. To learn more, read Fermented Foods: A Simple, Keto-Friendly Way to Boost Health and Well-Being.
- Consume magnesium-rich keto foods, such as fatty fish, leafy greens, avocados, and seeds.
- Consider supplementing with magnesium citrate when actively constipated, and magnesium glycinate or chloride on a more regular basis to support bowel regularity.
- Be careful with nuts and cheese, which can be binding for some people. Consume these only in small amounts or eliminate them altogether and note whether you see any improvement.
- Try adding medium-chain triglycerides (MCTs) or coconut oil, which contains MCTs that are rapidly absorbed and may help with constipation. Start with a small amount (½ to 1 tablespoon per day) to avoid gastrointestinal discomfort or overly loose stools, and gradually increase up to 2 tablespoons daily if needed.
- Stay physically active every day. Walk, dance, garden, bike, swim, perform cardio, lift weights, or do any other exercises that suit your preferences, ability, and schedule.
* Speak with your doctor about increasing sodium intake if you have kidney issues, high blood pressure, or have a serious medical condition.
The Bottom Line
Constipation on a ketogenic diet is often multifactorial and typically related to changes in fluid balance, electrolytes, and dietary composition.
In many cases, it can be improved by optimizing sodium and hydration; ensuring adequate fat, protein, and magnesium intake; and adjusting fiber intake based on individual response.
