Genetic and Environmental Factors in Diarrhea

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on diet & genetics. Browse all Diet & Genetics education

Diarrhea — loose or watery stools occurring more frequently than usual — is one of the most common health complaints, and it can be either short-lived (acute) or persistent (chronic). Its causes fall into two overlapping buckets: environmental triggers such as infections and foods, and genetic factors that shape how well the gut digests certain nutrients and regulates its lining. Understanding both helps explain why some people react to foods or exposures that others tolerate easily.

Environmental drivers of diarrhea

The most common causes are environmental. Viral, bacterial, and parasitic infections irritate the gut and pull water into the bowel. Contaminated food or water, certain medications (including some antibiotics), excess alcohol or caffeine, and high intake of poorly absorbed sugars and sugar alcohols can all provoke loose stools. Stress and travel disrupt normal gut rhythm as well. Most acute diarrhea is self-limited, but persistent or severe symptoms warrant evaluation.

Genetic factors in carbohydrate digestion

Some diarrhea is rooted in how the gut digests specific sugars, and that is strongly genetic. The LCT gene, regulated by a variant in the neighboring MCM6 gene (notably rs4988235), determines whether lactase activity persists into adulthood. People without the persistence variant produce less lactase, so undigested lactose ferments in the colon and can cause diarrhea, gas, and cramping after dairy. Separately, the SI gene encodes sucrase-isomaltase; inherited variants reduce the ability to break down sucrose and starch, a condition called congenital sucrase-isomaltase deficiency. These examples show how a single gene can determine tolerance to an entire class of food.

Inflammatory and gut-barrier genetics

Beyond carbohydrate digestion, genes that govern the gut's immune response and barrier integrity influence susceptibility to chronic diarrhea. Variants in NOD2, a gene involved in sensing bacteria and regulating intestinal immunity, are among the best-established genetic risk factors for Crohn's disease, in which diarrhea is a common symptom. Genes affecting the tight junctions between gut cells and the composition of the mucus layer also shape how the gut responds to microbes and food. These associations describe risk at the population level, not a guarantee for any individual.

General approaches to management

For most short-lived diarrhea, the priorities are staying hydrated and replacing lost fluids and electrolytes, resting the digestive system, and identifying and avoiding obvious triggers. When a specific food intolerance is involved — lactose, for example — recognizing and limiting that food often resolves symptoms. Persistent, bloody, or severe diarrhea, or diarrhea with weight loss, fever, or dehydration, should be assessed by a qualified healthcare provider, who can investigate underlying causes and recommend an appropriate plan rather than treating symptoms in isolation.

What a genetic test can and can't tell you

A genetic test provides pathway-level context about how your body handles foods and regulates key systems, not a diagnosis of any digestive condition. The Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights across peptide-related biological pathways. Variants such as those near LCT illustrate how genetics can shape food tolerance, but a wellness test does not tell you what to put in your body. It offers information to bring to a qualified provider — genetics as a guide, not a guarantee.

Frequently Asked Questions

Can diarrhea be genetic?

Partly. Many episodes come from infections or food, but genetics shapes how the gut digests certain nutrients and regulates its lining. Variants near the LCT gene affect lactose tolerance, the SI gene affects sugar and starch digestion, and NOD2 variants influence inflammatory bowel risk, all of which can involve diarrhea.

Why do I get diarrhea after dairy?

It is often lactose intolerance. A variant near the LCT gene (rs4988235 in MCM6) determines whether lactase persists into adulthood. Without it, you make less lactase, so undigested lactose ferments in the colon and draws in water, causing diarrhea, gas, and cramping after milk or dairy products.

When should I see a doctor about diarrhea?

See a qualified healthcare provider if diarrhea is severe, bloody, or lasts more than a few days, or if it comes with high fever, significant weight loss, or signs of dehydration such as dizziness and reduced urination. Chronic or recurrent diarrhea also deserves evaluation to identify the underlying cause.

Can a genetic test diagnose the cause of my diarrhea?

No. A wellness genetic test offers pathway-level context about food tolerance and related biology, not a diagnosis. Conditions causing chronic diarrhea are diagnosed clinically. Use genetic insight as background for a conversation with a qualified provider, never as a substitute for medical evaluation and testing.

Curious how your genetics fit into the bigger picture? The Precision Peptide Genetic Test offers pathway-level insight you can bring to a conversation with your healthcare provider — genetics as a guide, not a guarantee.

This article is part of the PlexusDx Education Hub. Browse all Diet & Genetics education

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.