Editor’s Note: This blog was written by Wael El-Nachef, MD, PhD, a gastroenterologist (GI) doctor, researcher and founder of the Parkinson Disease Gastrointestinal Clinic in California. Dr. El-Nachef kindly shared this information to help you and your loved ones learn more about how Parkinson’s disease (PD) affects the gut and what you can do to ease symptoms. Hear more from Dr. El-Nachef in our Ask the MD video and email him your questions at contact@PDGI.health.  

What is the “gastrointestinal tract”? 

The gastrointestinal tract is the technical term for the gut. It refers to the organ system encompassing the upper throat through the anus. This includes the esophagus (“food tube”), stomach, small intestine and colon.  

What does PD have to do with the gut? 

There are many theories regarding the role of the gut and the origin of PD. In fact, several studies now support the idea that PD may start in the gut and then spread to the brain in a subset of patients. These theories are very interesting and may improve our understanding of PD and potentially point to new treatments.  

But, regardless of the origin of an individual’s PD, most people with PD (PwP) have some form of gastrointestinal problems such as constipation, bloating or delayed gastric emptying, which is when food doesn’t move out of the stomach in a timely fashion. (More on this below.)  

Why do PwP have gastrointestinal problems? 

There are several possible reasons why PD can interfere with normal gut function. The gut houses as many nerve cells as the spinal cord (which is why it’s often referred to as “the second brain”). And it is possible that PD damages those nerve cells similarly to how it damages nerve cells in the brain. 

Another possibility is that PD damages the nerves that extend from the brain to the gut — the gut and the brain are literally connected! A malfunctioning in this gut-brain communication can also hinder normal functioning of the gut. 

There are multiple other possibilities, but ultimately the end result is usually gastrointestinal dysmotility, or a slowing down of gut movement. 

Can antibiotics/probiotics/prebiotics/fecal transplant or any other investigational treatment fix the microbiome and cure PD? 

Short answer: Not yet!  

There are several studies in pre-clinical models that suggest that the bacteria in the gut (the gut “microbiome”) may play a role in the cause and in the treatment of PD. There have also been studies in humans that show that the microbiome in PwP is different than the microbiome of people without PD. Also, there are a few human trials that suggest PD-related constipation may improve with fermented foods that naturally contain probiotics or with supplements containing probiotics. (Probiotics are “good bacteria” that are thought to have beneficial health effects.) 

That being said, the research on these questions is still very early. It is not clear if the changes we see in the microbiome of PwP are causing the PD or are a side effect of PD. Furthermore, there is not yet enough evidence to strongly support recommending the use of probiotics for PD.  

While we wait for more conclusive studies on these topics, I typically recommend that my patients eat a healthy, well-rounded diet including fruits, vegetables, and foods that naturally contain probiotics (just as I would for everyone!). 

What sort of gastrointestinal problems do PwP often experience? 

There are several ways PD can manifest in the gut, including constipation, bloating, delayed stomach emptying (gastroparesis), and difficulty swallowing. 

• Constipation: PwP may not have typical symptoms of constipation. In PD, constipation can take the form of decreased number of bowel movements, frequent but small bowel movements, difficulty passing bowel movements, liquid stools and even fecal incontinence (not making it to the bathroom on time). Teasing out the different possible symptoms to get the correct diagnosis can be tricky. 

• Bloating: The most common cause of bloating in PwP is un- or under-treated constipation. Sometimes, PwP will perceive delayed stomach emptying as bloating. Another potential, less common, cause of bloating is small intestinal bacterial overgrowth (SIBO). SIBO is not an infection, but it occurs when too many bacteria are present within the intestine. If the intestinal movements are slowed (which can be seen in PD), then the bacteria that are normally present don’t get periodically swept out of the intestine as frequently, allowing them to multiply. These bacteria produce gases like hydrogen and methane as byproducts of their own metabolism, and this leads to symptoms.  

• Gastroparesis: There are multiple reasons why a stomach may have delayed emptying, but often this is due to slow and disordered movement. People with gastroparesis may feel very full and uncomfortable after eating only a few bites of food. This can lead to decreased eating, which in turn can lead to weight loss and malnutrition. 

• Difficulty swallowing: swallowing problems can be caused by weakness in the muscles of the upper throat (which is usually treated by Speech and Swallowing Therapists or Ear, Nose and Throat [ENT] doctors) or by uncoordinated or slowed muscle movements in the esophagus. People with difficulty swallowing may cough or choke on food or water or feel like things get stuck in their chest. 

Editor’s note: Learn more about swallowing problems in PD.  

My levodopa doesn’t work as well as it used to — does this have anything to do with my gut? 

Possibly. Protein in food can interfere with the absorption of levodopa from the gut and into the body, and that is why we advise PwP to time their dosing of levodopa outside of mealtimes. However, this assumes that the stomach is emptying normally. 

If a PwP has delayed gastric emptying due to gastroparesis, protein from a meal may stick around in the stomach for much longer than normal and interfere with the absorption of levodopa, even if you follow the dosing instructions correctly.  

While we are still early in our understanding of the relationship of gastroparesis and levodopa absorption, I have seen many patients have improved response to levodopa after improving gastric emptying. My personal approach is to start a medication (such as prucalopride) that speeds up the GI tract if the patient has symptoms of slowed GI motility and is experiencing decreased effectiveness of levodopa despite appropriate timing of doses around meals. However, it is important to avoid medications such as metoclopramide (a medication commonly used for gastroparesis) as it can worsen PD symptoms.  

Additionally, there are tests that can measure how quickly the stomach empties. These include gastric emptying studies (an imaging study that measures how much food empties out of the stomach over time) and wireless motility capsules (a large pill you swallow that sends radio signals to a receiver and lets us know how long it takes to travel through the different segments of the GI tract). However, these tests are not always necessary, so I only consider those tests on a case-by-case basis. 

Editor’s note: Remember everyone is different! Speak with your personal physician about your symptoms and what may be best for you.  

How should I deal with constipation if I have PD? 

First and foremost: make sure you are up to date with your colon cancer screening! PD does not make you immune from things like colon cancer, which (excluding skin cancers) is the third most common cancer in men and women in the United States. While your GI symptoms are most likely due to PD, colon cancer can also cause these sorts of symptoms. For this reason, and because we can often successfully treat colon cancer or prevent it by removing polyps, routine colon cancer screening is essential. 

You can always start with over-the-counter treatments such as osmotic laxatives (polyethylene glycol), stimulant laxatives (bisacodyl or senna), as well as enemas or suppositories. However, if you find yourself requiring more than just occasional use, or if you have worrisome, “red flag” symptoms like blood in your stools, inability to have any bowel movements, abdominal pain, weight loss, vomiting, etc., then you should see a doctor as soon as possible. 

You can also try dietary changes to help manage constipation. Fruits, vegetables and legumes are great sources of fiber that can help with constipation. Also, prunes and other dried fruits, as well as chia seeds, can be effective in producing regular bowel movements. However, if these sorts of dietary changes are significantly worsening bloating or if you don’t know where to start, it might be best to seek the guidance of a dietitian who has experience with PD. 

Editor’s note: Before starting any treatment, including over-the-counter medications, talk with your personal provider.  

When should a PwP see a gastroenterologist? 

When I hear this question, I sense a concern about going to a specialist too soon. However, in the case of PwP, I have almost never seen someone “too soon.” I usually see them too late in the sense that they have been suffering with gastrointestinal symptoms for far too long before seeking expert care.  

It is reasonable to see a gastroenterologist if constipation persists despite occasional over-the-counter medication use, if you have unintentional weight loss, feel overly full from small meals, experience persistent and troublesome bloating, suffer from fecal incontinence or have difficulty swallowing. 

If possible, try to find a gastroenterologist who has experience with gastrointestinal motility issues — we’re sort of like movement disorder specialists for the gut! Depending on your situation, there could be very helpful treatments to address your gastrointestinal problems. Most academic or teaching hospitals will have a gastroenterologist who focuses on motility disorders.  

Again, if you are experiencing any of the worrisome or red flag symptoms listed above, contact your doctor right away. 

The medical information contained in this publication is for general information purposes only. The Michael J. Fox Foundation for Parkinson’s Research has a policy of refraining from advocating, endorsing or promoting any drug therapy, course of treatment, or specific company or institution. It is crucial that care and treatment decisions related to Parkinson’s disease and any other medical condition be made in consultation with a physician or other qualified medical professional.