December 1, 2025

BOSTON — A simple shift in eating habits may hold the key to preventing one of the most common and persistent complaints of aging, according to a major new study. Researchers from Mass General Brigham have found that following a Mediterranean or plant-based diet significantly lowers the risk of developing chronic constipation in older adults—a benefit that appears to be independent of fiber intake alone.

The findings, published in the journal Gastroenterology, challenge the conventional wisdom that fiber is the sole dietary factor in bowel regularity. While fiber remains important, the study suggests that the overall quality of a person’s diet—specifically one rich in whole foods and low in inflammation-causing processed items—plays a more critical role in gut motility than previously understood.

The “Whole Diet” Approach

Chronic constipation affects an estimated 15% to 30% of older adults, significantly impacting quality of life and costing the healthcare system billions annually. For decades, the standard medical advice has been straightforward: eat more fiber and drink more water.

However, this new analysis of over 96,000 participants from three major long-term health studies (the Nurses’ Health Study I and II, and the Health Professionals Follow-Up Study) reveals a more nuanced picture.

Researchers tracked the dietary habits and health outcomes of these middle-aged and older adults over several years. They found that those who adhered most closely to a Mediterranean diet had a 16% lower risk of developing chronic constipation compared to those with low adherence. Similarly, those following a plant-based dietary pattern saw a 20% risk reduction.

Conversely, diets associated with inflammation and highly processed foods had the opposite effect. Participants consuming a “Western” diet—characterized by red meats, refined grains, and sugary sweets—had a 22% increased risk of constipation. Those with the most pro-inflammatory diets faced a 24% higher risk.

It’s Not Just About the Fiber

Perhaps the most surprising finding was that these associations held true even when researchers statistically adjusted for total fiber intake. This means that two people could eat the exact same amount of fiber, but the one getting it from a diverse, plant-rich diet would be better protected against constipation than the one eating a processed diet supplemented with fiber.

“Healthy diets are known to ease constipation symptoms, but this study provides the first evidence that some eating patterns may help keep chronic constipation from starting in the first place,” said Dr. Kyle Staller, senior author of the study and a gastroenterologist at Massachusetts General Hospital.

“We have always assumed that the benefits of eating a healthy diet would be driven by fiber, but our analyses showed the benefit of these healthy diets on constipation were independent of fiber intake,” Staller added. “Our findings suggest that as we age, certain healthy diets may provide benefits to our gut beyond the known cardiovascular benefits.”

Why the “Inflammatory” Diet Hurts

The study highlights the potential role of systemic inflammation in gut health. The “Western” diet is known to trigger low-grade inflammation throughout the body, which may affect the nerves and muscles of the gut, slowing down transit time.

In contrast, the Mediterranean and plant-based diets are rich in anti-inflammatory compounds like antioxidants, polyphenols, and healthy fats (such as those found in olive oil and nuts). These nutrients may help maintain a healthy gut environment and microbiome, promoting regular bowel function in ways that fiber supplements alone cannot mimic.

Expert Perspectives

While this study focuses on prevention, its implications for daily life are significant. Dr. Lin Chang, a gastroenterologist and professor at the David Geffen School of Medicine at UCLA who was not involved in this specific study, has long emphasized the complex relationship between diet and gut symptoms.

“In general, people do well when they create a more routine schedule, eat a healthy diet and smaller more frequent meals,” Dr. Chang has noted in previous discussions on gut health. She cautions that while increasing fiber is important, it must be done gradually and as part of a balanced approach to avoid bloating and discomfort—a view that aligns with the new study’s emphasis on overall dietary patterns rather than just a single nutrient.

Dr. William Chey, a gastroenterologist at the University of Michigan, also notes that personalized nutrition is becoming key in treating functional bowel disorders. The new findings support the idea that a “one-size-fits-all” fiber prescription may be less effective than a holistic dietary upgrade.

Practical Takeaways for Better Gut Health

For those looking to protect their digestive health as they age, the research suggests moving beyond the fiber count on a nutrition label. Instead, focus on the broader pattern of what you eat:

Prioritize Plants: Make vegetables, fruits, legumes, and nuts the center of your meals.
Choose Healthy Fats: Swap butter and processed oils for olive oil, which is a staple of the Mediterranean diet.
Limit “Western” Staples: Reduce intake of red meats, fried foods, and refined sugars, which are linked to higher inflammation and constipation risk.
Don’t Ignore Fiber, But Don’t Rely on It Alone: Fiber is still essential, but it works best when it comes from whole food sources rather than supplements in a poor diet.

Limitations to Consider

While the study was large and comprehensive, it was observational, meaning it proves a link but not a direct cause-and-effect relationship. Additionally, diet and constipation symptoms were self-reported, which can introduce recall bias. However, the sheer size of the study and the consistency of the results across three different cohorts strengthen the validity of the findings.

As the population ages, these insights offer a “simple eating pattern,” as the researchers describe it, that could save millions from the discomfort of chronic constipation.

Medical Disclaimer

Medical Disclaimer: This article is for informational purposes only and should not be considered medical advice. Always consult with qualified healthcare professionals before making any health-related decisions or changes to your treatment plan. The information presented here is based on current research and expert opinions, which may evolve as new evidence emerges.

References

Primary Study: Wang, Y., Kuo, B., Berschback, M., Huttenhower, C., Chan, A. T., & Staller, K. (2025). Dietary Patterns and Incident Chronic Constipation in Three Prospective Cohorts of Middle- and Older-Aged Adults. Gastroenterology. DOI: 10.1053/j.gastro.2025.06.020