IBS symptoms cause a lot of discomfort. The primary symptoms of IBS in the gut include:

• Gas/bloating
• Abdominal pain & cramping
• Diarrhea
• Constipation
• Nausea
• Frequent trips to the bathroom

Most evidence points to changes in gut sensory function and motility as causes of IBS. But this information isn’t all that useful if you can’t determine what’s causing failure at both steps.

This is a topic I covered in a recent blog. A recent review found that most people with IBS have a treatable, underlying cause. No matter the cause, the outcome is the same: impaired gut sensory function and motility. As a result, addressing the underlying cause(s) corrects IBS symptoms.

Glucagon-like peptide 1(GLP-1) is a hormone secreted in the gut in the presence of food. So, in essence, GLP-1 plays a role in gut sensory function. Additionally, GLP-1 affects gut motility throughout the intestine. Although, the effects are specific to the section of the intestine.

This begs the question, does GLP-1 play a role in IBS? Fortunately, another recent review covers this topic nicely.

GLP-1 and IBS symptoms

Enteroendocrine cells in the stomach, intestine, and pancreas secrete GLP-1 and a host of other hormones that participate in digestion. L cells are the specific type of enteroendocrine cell that secrete GLP-1.

Nutrients stimulate the secretion of GLP-1 in a site-dependent manner. This means that different factors cause the secretion of GLP-1 depending on where we’re looking. For example:

• Nutrients such as sugars, amino acids, and fatty acids cause GLP-1 secretion in the stomach and upper small intestine.
• Bile acids and bacterial metabolites such as short chain fatty acids, indole cause GLP-1 secretion in the lower small intestine and colon.

In addition, different areas of the gut respond differently to GLP-1. For example, GLP-1 decreases motility in the stomach and upper small intestine. This effect decreases appetite and prevents hyperglycemia by slowing digestion. But in the colon, GLP-1 increases motility.

GLP-1 likely exerts its effect on IBS by regulating gut sensory function and gut motility. But other factors are likely in play as well. Some of these factors are gut specific, but others may occur throughout the body.

GLP-1 has functions elsewhere in the body. In the pancreas, it promotes insulin secretion with meals. This helps keep blood glucose levels stable. GLP-1 also increases beta cells, the cells in the pancreas that secrete insulin, and insulin storage.

Finally, GLP-1 may play a role in other organs. This includes the brain, muscle, bone, lungs, kidneys, liver and heart.

GLP-1 and circadian rhythms

GLP-1 follows a circadian rhythm that plays a role in insulin sensitivity. Secretion of GLP-1 due to feeding is highest at the beginning of the normal active phase. Also, the pancreas secretes more insulin when exposed to GLP-1 at the same time.

Any hormone released due to feeding is likely to have an important effect on circadian rhythms. Additionally, the importance of GLP-1 to circadian rhythms is bolstered by its effects on insulin. Researchers recently identified insulin/IGF-1 as the primary signal entraining circadian rhythms to feeding.

I believe this is one of the reasons that insulin resistance/Type 2 diabetes is terrible for gut health. People with Type 2 diabetes have impaired GLP-1 signaling. They also have several signs of circadian disruption, and circadian disruption promotes Type 2 diabetes.

Drugs that mimic GLP-1 are currently used for Type 2 diabetes. The major side effect of these drugs is gastrointestinal problems. That’s the problem with tinkering with single mechanism approaches to complex diseases.

As with everything else in the human body, it’s not quite that simple. Other factors play a role in GLP-1 secretion outside of feeding. Furthermore, optimizing circadian rhythms requires the integration of many signals throughout the body. It’s not just about light and feeding.

Conclusion

GLP-1 is a hormone secreted by the gut in response to nutrients, bile acids, and bacterial metabolites. It plays a role in regulating gut motility, food intake, and insulin secretion. However, its effects differ depending on where it is in the gut.

GLP-1 may play a role in causing IBS symptoms. Its secretion due to eating matches up with symptoms of IBS worsening after meals. It is also front and center with the 2 primary mechanisms behind IBS symptoms: altered sensory activity and motility.

GLP-1 is also under circadian regulation and interacts with other circadian hormones. Altering light exposure or meal timing in rats alters the circadian variation of GLP-1 secretion by L cells. In our next blog we’ll cover another major circadian hormone that works with GLP-1 and may also have a role in IBS.