Constipation is common in people with diabetes, but constipation itself does not usually cause a direct, predictable rise in blood glucose. The relationship is more complicated: diabetes—particularly long-standing or poorly controlled diabetes—can contribute to constipation through gastrointestinal dysfunction and autonomic neuropathy, while constipation, dietary changes, dehydration and associated gastrointestinal problems can make diabetes management more difficult. PubMed

For people with diabetes, persistent constipation therefore deserves attention—not because every episode indicates poor glucose control, but because it can sometimes be a manifestation of diabetic gastrointestinal complications or medication-related gastrointestinal effects.

Can Constipation Raise Blood Sugar?

Usually, not directly.

Constipation primarily affects bowel movement and stool passage. It does not itself cause the same direct increase in blood glucose that carbohydrate intake, insufficient insulin, infection or certain medications can cause.

However, there can be an indirect relationship.

Diabetes and constipation can influence each other through several pathways:

Diabetes → gastrointestinal dysfunction → constipation

and, in some people:

Constipation/GI symptoms → altered eating, hydration and medication patterns → more difficult glucose management

Research has found associations between constipation and poorer glycemic control, but an association does not prove that constipation itself causes hyperglycemia. A study in people with diabetes found constipation symptoms were associated with HbA1c ≥8%, while another study found constipation symptoms correlated with HbA1c. PubMed

Why Is Constipation More Common in Diabetes?

Several mechanisms may contribute.

1. Diabetic autonomic neuropathy

Long-standing diabetes can damage autonomic nerves that regulate gastrointestinal function.

These nerves influence:

• Intestinal movement
• Colonic transit
• Rectal function
• Sphincter coordination

The American Diabetes Association’s 2026 Standards of Care identifies constipation, diarrhea, gastroparesis and fecal incontinence among manifestations of diabetic autonomic neuropathy. Diabetes Journals

Constipation may therefore be one manifestation of diabetic gastrointestinal neuropathy, particularly in people with long-standing diabetes.

2. Chronic hyperglycemia

Persistently elevated glucose may contribute to changes in gastrointestinal nerve function and intestinal motility.

The relationship is complex. Hyperglycemia can affect gastrointestinal motor function, while gastrointestinal dysfunction can subsequently influence glucose absorption and glucose variability. PubMed

This means that the relationship is bidirectional rather than simply “constipation causes high sugar.”

3. Reduced physical activity

Physical inactivity can contribute to both:

• Poor glycemic control
• Constipation

Regular physical activity supports bowel motility and is also an important component of diabetes management.

4. Low-fiber dietary patterns

Some people with diabetes may consume insufficient:

• Vegetables
• Whole grains
• Pulses
• Fruits
• Other fiber-rich foods

A low-fiber diet can contribute to constipation.

However, increasing fiber should be individualized. People with certain gastrointestinal conditions or advanced kidney disease may require a different dietary approach.

5. Dehydration

High blood glucose can increase urinary water loss when glucose levels are sufficiently elevated to cause glycosuria.

Dehydration can contribute to harder stools.

Therefore, a person with diabetes who has both significant hyperglycemia and constipation should consider whether inadequate fluid intake, increased urination or another underlying problem is contributing.

Can Constipation Cause Blood Sugar to Go Up?

There is no strong evidence that ordinary constipation directly causes a clinically important rise in blood glucose in otherwise stable diabetes.

However, constipation can occur alongside factors that disturb glucose control.

For example:

Constipation → reduced appetite or altered meals → altered diabetes medication/food intake → glucose variability

or:

Poor diabetes control → dehydration + gastrointestinal dysfunction → constipation

This is why it is better to look for the underlying cause rather than treating constipation and glucose as completely separate problems.

Constipation May Sometimes Be a Sign of Poorly Controlled Diabetes

This does not mean that every person with constipation has uncontrolled diabetes.

But studies have identified an association between constipation and poorer glycemic control. In one study, constipation was associated with HbA1c ≥8%, longer diabetes duration and other diabetes-related factors. PubMed

Another study found that HbA1c was correlated with constipation symptoms and anorectal sphincter pressure in people with type 2 diabetes. PubMed

Therefore, new or persistent constipation in a person with diabetes should prompt a review of overall diabetes control and other possible causes.

Is Constipation Always Due to Diabetic Neuropathy?

No.

This is an important clinical distinction.

Constipation in someone with diabetes can have many causes, including:

• Low dietary fiber
• Inadequate fluid intake
• Physical inactivity
• Irritable bowel syndrome
• Functional constipation
• Hypothyroidism
• Electrolyte abnormalities
• Structural bowel disease
• Medication effects
• Diabetic autonomic neuropathy

The ADA specifically notes that gastrointestinal neuropathies are diagnoses of exclusion and that medication-related gastrointestinal adverse effects should be considered. Diabetes Journals

Diabetes Medicines Can Also Affect the Gastrointestinal Tract

When constipation develops after starting or changing medication, the medication history should be reviewed.

Different diabetes and non-diabetes medicines can affect gastrointestinal function.

The 2026 ADA Standards specifically advise considering medication-related gastrointestinal effects, including those associated with metformin and GLP-1-based therapy, when evaluating gastrointestinal symptoms. Diabetes Journals

Importantly, gastrointestinal effects vary between individuals and between medicines. A patient should not stop diabetes medication simply because constipation occurs without discussing it with the treating clinician.

What Should a Person With Diabetes Do About Constipation?

The first step is to identify the likely cause.

Review:

• Blood glucose pattern
• HbA1c
• Diet and fiber intake
• Fluid intake
• Physical activity
• Medication history
• Duration of constipation
• Stool consistency
• Frequency of bowel movements
• Abdominal symptoms
• Other autonomic symptoms

If constipation is persistent, recurrent or associated with other symptoms of autonomic dysfunction, further evaluation may be appropriate.

Diet and Constipation in Diabetes

A diabetes-friendly approach can often include naturally fiber-rich foods such as:

• Vegetables
• Pulses and dals
• Whole grains
• Fruits in appropriate portions
• Nuts and seeds
• Other minimally processed plant foods

The objective is not simply to add large quantities of fiber.

A sudden increase in fiber can cause:

• Bloating
• Gas
• Abdominal discomfort

Fiber intake should therefore be increased gradually and individualized.

People with kidney disease, bowel obstruction, severe gastroparesis or other gastrointestinal conditions may require specific dietary modifications.

What About Isabgol/Psyllium?

Psyllium is a soluble fiber that can be useful for constipation in appropriate individuals.

It can also influence post-meal glucose response because soluble fiber slows carbohydrate absorption.

However, it should be used appropriately, with adequate fluid intake and consideration of the individual’s medical conditions and medications.

Persistent constipation should not simply be managed indefinitely with self-treatment without identifying the cause.

Does Better Blood Sugar Control Improve Constipation?

It may help when hyperglycemia is contributing to gastrointestinal dysfunction, but improvement is not guaranteed.

Diabetic gastrointestinal dysfunction can involve multiple mechanisms, including neural, muscular and cellular changes. Long-standing complications may not immediately reverse simply because glucose improves. PubMed

Therefore:

Good glycemic control is important, but persistent constipation still needs its own evaluation.

When Constipation in Diabetes Needs Medical Evaluation

Seek medical assessment if constipation is:

• Persistent or recurrent
• New and unexplained
• Associated with significant abdominal pain
• Associated with vomiting
• Associated with abdominal distension
• Associated with unexplained weight loss
• Associated with blood in the stool
• Associated with anemia
• Associated with a significant change in bowel habits
• Associated with alternating constipation and diarrhea
• Associated with difficulty swallowing or persistent upper-GI symptoms

These features may indicate a condition other than uncomplicated functional constipation.

Constipation Plus Other Autonomic Symptoms

The possibility of diabetic autonomic neuropathy becomes more relevant when constipation occurs together with symptoms such as:

• Dizziness on standing
• Resting tachycardia
• Abnormal sweating
• Urinary retention or incontinence
• Erectile dysfunction
• Gastroparesis symptoms
• Early satiety
• Nausea or vomiting

The ADA recommends assessment for autonomic neuropathy in people with diabetes and specifically includes constipation among the symptoms that should be elicited during clinical assessment. Diabetes Journals

Does Constipation Affect HbA1c?

There is no evidence that constipation itself directly increases HbA1c.

HbA1c reflects average glycemia over approximately the preceding 2–3 months.

If constipation is associated with a higher HbA1c, possible explanations include:

• Poorer diabetes control contributing to GI dysfunction
• Dietary changes
• Reduced physical activity
• Medication-related effects
• Dehydration
• Shared metabolic risk factors

Observational studies have demonstrated an association between constipation and poorer glycemic control, but this should not be interpreted as proof that constipation independently causes higher HbA1c. PubMed

Constipation and Blood Sugar: The Clinical Relationship

Key Takeaways for People With Diabetes

1. Constipation does not usually directly raise blood sugar.

The relationship is more complex than a simple cause-and-effect relationship.

2. Diabetes can contribute to constipation.

Long-standing diabetes, hyperglycemia and autonomic gastrointestinal dysfunction can affect bowel motility. PubMed

3. Persistent constipation deserves attention.

It may be related to diet, hydration, medication, thyroid disease, bowel disorders or diabetic autonomic neuropathy.

4. Don’t stop diabetes medication on your own.

If constipation began after a medication change, discuss the timing with your clinician.

5. Look at the whole diabetes picture.

Review:

HbA1c + glucose pattern + medications + diet + hydration + activity + bowel symptoms.

6. Red-flag symptoms require medical evaluation.

Blood in stool, unexplained weight loss, severe abdominal pain, vomiting, marked abdominal distension or a significant persistent change in bowel habits should not simply be attributed to diabetes.

Bottom Line

Constipation does not usually cause high blood sugar by itself. Rather, diabetes and constipation can be connected through hyperglycemia, gastrointestinal motility abnormalities, autonomic neuropathy, diet, hydration, physical activity and medication effects.

For someone with diabetes who develops persistent constipation, the appropriate approach is not simply to take a laxative or assume that constipation is causing the glucose problem.

A better approach is to ask:

Is diabetes adequately controlled?
Could a medication be contributing?
Is the diet providing enough appropriate fiber and fluid?
Could autonomic neuropathy be present?
Are there other gastrointestinal or metabolic causes?

This approach can help distinguish ordinary constipation from a potentially important manifestation of diabetic gastrointestinal disease. PubMed

Evidence & References

1. Constipation in DM are associated with both poor glycemic control and diabetic complications: Current status and future directions. PubMed. PubMed
2. Standards of Care in Diabetes—2026: Retinopathy, Neuropathy, and Foot Care. American Diabetes Association. Diabetes Journals
3. Digestive, Anorectal, and Urogenital Functions in Patients With Type 2 Diabetes Mellitus, Impaired Glucose Tolerance and Normal Glucose Tolerance. PubMed. PubMed
4. Constipation, hard stools, fecal urgency, and incomplete evacuation, but not diarrhea is associated with diabetes and its related factors. PubMed. PubMed
5. Diabetic Gastroenteropathy: Soothe the Symptoms or Unravel a Cure? PubMed. PubMed
6. Diabetes and the Small Intestine. PubMed. PubMed

PubMed – National Library of Medicine
American Diabetes Association – Standards of Care 