The two most common GI problems people experience on keto are diarrhea and constipation. Diarrhea most often results from use of MCT oil or consumption of sugar alcohols, both of which are notorious for causing loose stools when overconsumed. However, “overconsumed” is a relative term. Some people may experience gas, bloating, and loose stools after eating only a small amount of MCT oil or products sweetened with sugar alcohols. (Erythritol has the lowest likelihood of inducing these symptoms, while maltitol, mannitol, xylitol, and sorbitol tend to be bigger culprits.
If you’re faced with a patient complaining of diarrhea on keto, ask them about their intake of MCT oil and sugar-free candy (especially chocolate) sweetened with sugar alcohols. The good news is, despite the buzz about it on social media, MCT oil is not required on a keto diet. People were getting excellent results with weight loss and reversal of chronic metabolic problems long before MCT oil was readily available at grocery stores. Completely eliminating sugar-free treats is a taller order, but they don’t have to be avoided entirely. Some people may fare better with products sweetened with erythritol or allulose, as these are less likely to cause GI distress at moderate intake levels.
Patients who’ve had their gallbladder removed may experience oily stools or stomach upset when they’re new to keto. Most people without a gallbladder can follow a keto diet with no modifications needed, but for those who run into these issues, it may be best to transition slowly to a higher fat diet rather than making the shift all at once. (It’s important to note, however, that keto is not necessarily a very high-fat diet. What it really is, is very low-carb. The percentage of total calories coming from fat on a ketogenic diet may be higher than what someone was eating previously, but the absolute grams of fat often aren’t much different. In fact, overdoing fat—particularly from nuts, cheese, heavy cream, and other fat-dense foods—is a common reason for stalled or slow weight loss on a keto diet.)
What about the opposite problem – constipation? The explanation that makes the most sense on the surface is that owing to the very low carbohydrate intake required on a ketogenic diet, people consume much less fiber. However, as we covered in a past article, a high fiber intake doesn’t always “get things moving” – in fact, it can sometimes make constipation worse. The more likely explanation for constipation on ketogenic diets is a simple misunderstanding of what defines constipation. Many people think it’s essential to have a bowel movement every day, but this isn’t true.
According to the American Society of Colon & Rectal Surgeons:
“The belief that one must have a bowel movement every day simply is not accurate and can lead to unnecessary concern and even abuse of laxatives. In fact, if one’s daily bowel movement is hard, requires great effort to expel, or does not satisfactorily empty, the individual would still be considered to have constipation in spite of having a ‘normal’ frequency. On the contrary, if one has a bowel movement every third day but it is not hard, does not require straining, and completely evacuates, then one may very well consider this a “normal” bowel movement.”
So, some patients who report constipation while following a keto diet may simply be having fewer bowel movements than they’re accustomed to. If so, this is not a problem in need of a solution. But for those who genuinely do have constipation rather than just reduced frequency, the corrective measures are simple: increasing salt (sodium) intake typically helps, and supplementing with magnesium is also effective. Other factors that contribute to constipation regardless of one’s diet may also play a role for some people, so making sure hydration is adequate can help if someone has been skimping on water intake, and physical activity is encouraged. And for the subset of people for whom a higher fiber intake does help GI motility, they can experiment with increasing consumption of leafy greens and other non-starchy vegetables to see if that offers relief while still allowing them to experience the benefits of carbohydrate restriction.