The pancreas produces a hormone called insulin, which helps regulate the metabolism of carbohydrates in the body by signaling cells to take in glucose from the bloodstream. Diabetes occurs when the pancreas does not produce enough insulin, or when cells in the body do not respond to insulin the way they should.

There are three main types: type 1 diabetes, type 2 diabetes, and gestational diabetes. In type 1 diabetes, the pancreas produces very little or no insulin. It often occurs in children, and is a form of autoimmune dysfunction. Type 2 diabetes is more common than type 1, affecting approximately 90% of those with diabetes.1 It occurs more frequently in adults older than 40 years-of-age, although physicians have been diagnosing type 2 diabetes in younger individuals more often in recent years.2 Type 2 diabetes typically involves insulin resistance, which means that the body does not respond to and metabolize insulin effectively. In some cases, type 2 diabetes occurs when the body does not produce sufficient insulin. Gestational diabetes only occurs during pregnancy in women who did not have diabetes beforehand, but developed high blood sugar while pregnant. Most of the time, gestational diabetes resolves after pregnancy, but it can increase the risk of the woman or her child developing diabetes in the future. Gestational diabetes can also put women at an increased risk of developing complications during pregnancy, such as preeclampsia.3

In this article, we will review some of the basics, as well as the ways in which diabetes can affect the digestive tract and cause painful gastrointestinal symptoms.


Diabetes Symptoms and Diagnosis

The most common symptoms of any type of diabetes are extreme thirst and frequent urination, increased appetite, fatigue or exhaustion, dry skin, and vision changes (such as blurred vision). In more severe cases, symptoms can include unexplained weight loss or gain, slow-healing injuries, frequent illness or infections (especially yeast infections), and pain or numbness in the hands or feet. Long-term complications of diabetes can include kidney disease, cardiovascular disease, vision loss, and lower limb amputation.4 Those with type 2 diabetes might not experience any symptoms at first, or just one symptom, such as feeling slightly thirstier than previously. Type 1 diabetes tends to be more severe, especially in young children, who can experience weight loss and failure to thrive.

Your physician will order blood tests to assess fasting glucose as well as your average glucose levels over the last two to three months (HbA1c) and, depending on your results, will determine whether you have normal levels, prediabetes, or some form of diabetes.


Diabetes Statistics

Diabetes is very common. According to Statistics Canada,5 diabetes occurs in 7% of Canadians 12 years-of-age or older. It is slightly more common in males (7.6%) than in females (6.4%). Diabetes prevalence increases with age, with the highest prevalence in those 65-74 years-of-age. In addition, obesity is associated with a higher prevalence of diabetes. Of Canadians who are at a normal, healthy weight, only 3.6% have diabetes, but 6.6% of those who are overweight have diabetes, and 13.2% of those who are obese have diabetes.


Diabetes and Gastroparesis

Diabetes is the leading cause of gastroparesis, a digestive condition in which food remains in the stomach for too long (delayed gastric emptying), rather than passing into the small intestine when it should. High blood sugar from diabetes can cause chemical changes in the vagus nerve, which connects the brainstem to the gastrointestinal tract. This impedes the vagus nerve’s normal ability to send messages that prompt the stomach muscles to empty the stomach. Diabetic gastroparesis is an especially dangerous form of gastroparesis, because the delayed gastric emptying can lead to periods of very high or very low blood sugar, continuing to worsen the vagus nerve damage.

Gastroparesis symptoms include nausea, vomiting, reduced appetite, feeling full after eating small amounts of food, abdominal pain, and heartburn. While these symptoms are already often debilitating, gastroparesis patients’ inability to eat enough can cause many complications. Nutrient deficiencies are common, and these can lead to fatigue, weight loss, and anemia. In some cases, excessive vomiting can cause severe dehydration.


Diabetic Autonomic Neuropathy

Diabetes is the most common cause of a serious condition known as autonomic neuropathy. Diabetic autonomic neuropathy involves peripheral nerve dysfunction, and affects many parts of the body, with significant gastrointestinal symptoms.6 It often gets continually worse and can be fatal for some individuals.

Diabetic autonomic neuropathy often affects the cardiovascular system, respiratory system, and other parts of the body, but we will be focusing on its effects on the digestive tract. As mentioned in the section on gastroparesis, diabetes can affect proper functioning of the nervous system. When neuropathy affects the enteric nervous system, which is the nervous system of the gut, it can cause many digestive symptoms including constipation, diarrhea, fecal incontinence, and esophageal dysmotility.

There are currently no treatments available to effectively reverse the progression, so prevention is extremely important. The best way to prevent diabetic autonomic neuropathy is to ensure that your blood sugar levels are always under control.


Celiac Disease and Type 1 Diabetes

While it is unclear exactly what the relationship is, some research has found that those with celiac disease are more likely than the general population to develop type 1 diabetes. One 2015 study found that type 1 diabetes affected only 0.4% of the control subjects, but 3.2% of those with celiac disease.7


Pancreatitis and Diabetes

The pancreas is the organ responsible for producing insulin. In some individuals with pancreatitis, the damage incurred from inflammation can impede the pancreas’ ability to produce insulin, causing diabetes. One study found that individuals who experienced acute pancreatitis had a greatly increased chance of developing diabetes (23%) compared with the general population (4-9%).8


Diabetes Medications

The medication metformin revolutionized type 2 diabetes treatment and is the most widely used oral diabetes medication. Although it was discovered in 1922, human studies did not take place until 1950s. It was introduced as a medication in France in 1957, Canada in 1972, and the United States in 1995. It is on the World Health Organization’s List of Essential Medicines, the most effective and safe medicines needed in a health system.

Individuals with milder cases of diabetes can take metformin with relatively few side effects to manage their blood sugar levels. However, metformin has some notable side effects in the digestive tract, including diarrhea, fecal urgency, nausea, and abdominal pain. These symptoms often disappear after the individual adjusts to the medication, but in some cases, diarrhea can last for a long time. It is also common for diarrhea to cease if the patient stops taking metformin, then to return if they resume metformin. The upside is that metformin has been shown to have other benefits such as lowering cholesterol, improving erectile dysfunction, and reversing fatty liver disease.9,10,11


Food Choices and Gut Health

Many individuals with diabetes choose to consume artificially sweetened treats in lieu of those containing sugar. However, it is important to note that a certain type of artificial sweetener, known as sugar alcohols, can cause diarrhea. These include erythritol, sorbitol, maltitol, and xylitol; in general, look for products that contain ingredients that end in “itol”. Avoid large quantities of these products to reduce diarrhea.

In addition, some individuals with diabetes might limit overall carbohydrate intake, which can make it difficult to consume enough fibre. Dietary fibre is vital to a well-functioning gut, and not getting enough can lead to constipation or diarrhea. Beyond maintaining healthy bowel function, some research shows that fibre might help to regulate blood sugar levels by slowing digestion and by modifying gut bacteria.12


Digestive Ailments are Common in Those with Diabetes

In a study published in 2018, researchers asked 706 individuals with type 1 diabetes, and 604 individuals without diabetes, a series of questions about their gastrointestinal symptoms and quality of life.13 They found that lower gastrointestinal symptoms – including constipation, diarrhea, abdominal pain, bloating, intestinal gas, and floating stools – were much more common in the individuals with diabetes, especially diarrhea and constipation, which were twice as likely in those with diabetes. These symptoms were associated with lower quality of life and poor glycemic control. However, the researchers were able to identify, and treat accordingly, the cause of diarrhea in 72% of cases, leading to a better outcome for the patients. If you have diabetes and experience digestive symptoms, make sure to let your health care team know so that you can work together to manage these symptoms.



Diabetes can affect many parts of the body, especially the digestive system. If you are experiencing unusual gastrointestinal symptoms, it is important to speak with your health care team, so you can find out the cause and work on treatment options.

First published in the Inside Tract® newsletter issue 206 – 2018
Photo: | stevepb
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