Diarrhea After Stomach Cancer Treatment: Is it Common and How to Manage It

Diarrhea can be a common side effect during and after treatment for stomach (gastric) cancer, and it can happen for several reasons including chemotherapy, radiation, immunotherapy, targeted therapies, surgery, and infections. ^{[1] [2]} Cancer treatments such as chemotherapy often list diarrhea among expected side effects, while radiation to the abdomen, immunotherapies, and some targeted drugs can also contribute. ^{[1] [2]} If part of the intestine is removed during surgery, digestion can change and lead to looser stools as well. ^[2]

Why Diarrhea Happens in Stomach Cancer Care

• Chemotherapy can irritate the lining of the gut and speed up bowel movements, leading to loose, watery stools. ^[1]
• Radiation to the abdomen can inflame the intestines (acute enteritis), with 30–50% experiencing diarrhea; rates are higher when combined with chemotherapy. ^{[3] [4]}
• Immunotherapy can trigger inflammation of the colon (immune-related colitis), which causes diarrhea that may need specific treatment. ^[5]
• Targeted therapies can also cause gastrointestinal side effects, including diarrhea, because they affect proteins in normal tissues. ^[6]
• Surgery on the stomach or intestines may change digestion and absorption, sometimes resulting in diarrhea. ^[2]
• Infections and antibiotics used to treat them can also cause diarrhea during cancer treatment. ^[2]

When to Contact Your Care Team

Some diarrhea is expected, but certain signs suggest it could be serious or lead to dehydration and need prompt medical attention. ^[7]

• Six or more loose bowel movements a day for more than two days is a reason to call right away. ^[7]
• Blood in the stool, signs of dehydration (such as very dark urine, dizziness, dry mouth, or low urine output), fever, or worsening weakness also warrant urgent contact. ^[7]
• If you are taking oral chemotherapy pills and develop diarrhea, ask if it is safe to continue before taking the next dose. ^[8]

At-Home Management: First Steps

• Hydration: Aim for frequent clear fluids and include some with electrolytes (e.g., broths, oral rehydration drinks) to replace losses. ^[9]
• Diet shift: Start with clear liquids when diarrhea begins, then add low-fiber, binding foods like bananas, white rice, applesauce, and toast (the “BRAT” style) as symptoms improve. ^{[9] [10]}
• Smaller, frequent meals: Eating 6–8 small meals can be gentler on the gut. ^[10]
• Avoid triggers: Limit high-fat, spicy foods, caffeine, alcohol, and high-fiber roughage while symptoms are active; consider cautious dairy avoidance if it worsens stools. ^[10]
• Rest the gut: During intense bouts, lighter intake (clear liquids) for a short period may help before slowly reintroducing bland foods. ^[11]

Medications and What’s Safe

• Over‑the‑counter loperamide (Imodium) can help control diarrhea, but check with your oncology team before starting any new medicine during active treatment. ^{[12] [13]}
• Avoid stool softeners and laxatives while you have diarrhea. ^[12]
• If diarrhea is due to immunotherapy (immune-related colitis), you may need a different plan directed by your team, sometimes including steroids or holding treatment. ^[5]

Special Notes for Radiation-Related Diarrhea

Radiation to the abdomen can cause both short‑term and longer‑term diarrhea due to irritation and changes in absorption and gut motility; risk is higher with larger doses and when chemotherapy is given at the same time. ^{[3] [14] [4]} Close communication with your radiation oncology team helps tailor antidiarrheal use, diet, and hydration to your regimen and symptoms. ^[3]

Practical Diet Tips You Can Try

• Choose low-fiber starches (white rice, pasta, potatoes without skin), lean proteins (chicken, eggs, tofu), ripe bananas, applesauce, and smooth nut butters. ^{[9] [10]}
• Sip fluids throughout the day; target a cup after each loose stool to keep up with losses. ^[15]
• After meals, resting for 30 minutes can sometimes slow digestion and reduce urgency. ^[15]

Red Flags and Dehydration Symptoms

Watch for increased thirst, dry mouth/skin, darker urine, fatigue, cramps, or dizziness/lightheadedness, which may signal dehydration and the need for medical review. ^[16] If these occur, contact your care team promptly to avoid complications. ^[7]

Key Takeaways

• Diarrhea is common during stomach cancer treatment and can result from chemotherapy, radiation, immunotherapy, targeted therapies, surgery, infections, or antibiotics. ^{[1] [2]}
• Start with hydration, low‑fiber/bland foods, small frequent meals, and avoid gut irritants; consider loperamide if your team approves. ^{[9] [10] [12] [13]}
• Seek help urgently for persistent frequent loose stools, blood, dehydration signs, fever, or if you’re on oral chemo and not sure whether to continue. ^{[7] [8]}

By addressing symptoms early and using supportive strategies, most people can reduce diarrhea’s impact and stay on track with treatment. ^[17]