Stomach Cancer

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.²⁷ Nothing on this page treats stomach cancer. The most effective preventive step here is not nutritional: get tested for H. pylori and treated if you have it, because eradication is the one intervention with randomized trial evidence for reducing gastric cancer risk. Diet matters at the population level, mainly through less salt and preserved food and more vegetables, but those associations are observational and are not treatment. After gastrectomy the nutrition on this page becomes genuinely important, because the surgery permanently changes what you can absorb: vitamin B12 requires lifelong replacement, iron and calcium absorption fall, and dumping syndrome is common. That belongs with a specialist dietitian, not a supplement aisle. Tell your oncology team about every supplement you take. Diet and supplements are not an alternative to surgery, chemotherapy, radiation therapy or immunotherapy, and no dietary change should delay or replace treatment decided with your oncology team. Several supplements interact with cancer treatment.

1. IARC Monographs classify Helicobacter pylori as a Group 1 carcinogen. Roughly 60 to 90% of non-cardia gastric cancers are attributable to chronic infection, a range reflecting the detection method used: the worldwide attributable fraction is 74.7% on ELISA-based data and 89.0% on immunoblot (Plummer M, et al. Int J Cancer. 2015;136(2):487-⁠490. PubMed 24889903). Chronic infection drives the progression from gastritis to atrophic gastritis to intestinal metaplasia to dysplasia. Cardia and gastro-esophageal junction cancers behave differently and are linked to reflux, Barrett's esophagus and obesity rather than to H. pylori. ↩
2. On H. pylori eradication, which is why this page separates it from dietary advice. Randomized trials and their meta-analyses, including Cochrane reviews of eradication for gastric cancer prevention, show that treating H. pylori reduces subsequent gastric cancer incidence in infected people. That is a different grade of evidence from the dietary associations on this page, which come from observational cohorts. Antioxidant supplementation trials for digestive cancer prevention are mixed, with no convincing benefit across 20 randomized trials, PubMed 18677777. Eradication is a prescription antibiotic course, not a supplement. ↩
3. On hereditary diffuse gastric cancer: CDH1 germline mutations underlie a distinct diffuse-type disease, often of younger onset. Carriers are managed differently, including consideration of prophylactic gastrectomy. Family history of gastric cancer at a young age warrants genetic referral. ↩
4. On what IARC Group 1 means: the classification describes the strength of the evidence that something causes cancer, not the level of risk, so agents in the same group are not equally dangerous. Processed meat is in Group 1 on the evidence for colorectal cancer; an association with stomach cancer was seen, but the evidence is not conclusive, WHO, questions and answers on red and processed meat. ↩
5. On surveillance of precancerous changes: a 2021 expert review advises that everyone with atrophic gastritis be tested for H. pylori and treated if positive, with eradication confirmed; that a surveillance endoscopy every 3 years be considered in advanced atrophic gastritis, with the interval otherwise set by individual risk and shared decision making; and that people with autoimmune gastritis be checked for vitamin B12 and iron-deficiency anemia, PubMed 34454714. ↩
6. SEER (National Cancer Institute) stomach cancer statistics, and GLOBOCAN/IARC for global figures. seer.cancer.gov. Source for the estimate of 31,510 new US cases in 2026, the overall 5-⁠year relative survival of 39.8% for 2016 to 2022 (78.1% when the cancer is found while still localized), and the global ranking. Incidence has fallen substantially in Western countries, attributed largely to refrigeration replacing salt preservation and to declining H. pylori prevalence. ↩
7. On treating H. pylori: a Cochrane review of seven randomized trials in 8,323 healthy adults with the infection, six of them in Asian populations, found that eradication treatment lowered the incidence of gastric cancer (risk ratio 0.54) and deaths from it (risk ratio 0.61) compared with placebo or no treatment, with moderate certainty, while noting the results may not extend to other populations. The treatment is a prescribed antibiotic course, PubMed 32628791. ↩
8. On salt: WHO recommends that adults eat less than 2,000 mg of sodium a day, equivalent to less than 5 g of salt, just under a teaspoon. It is a general population target, not a cancer-specific dose, WHO, sodium reduction. ↩
9. On emergencies: NHS guidance advises calling emergency services for vomiting bright red blood or vomit that looks like ground coffee, stools that contain blood or are black, sticky and very smelly, or severe abdominal pain, and getting urgent same-day advice for anyone who keeps vomiting and cannot keep fluids down, NHS, stomach ulcer, NHS, diarrhea and vomiting. ↩
10. On risk factors: the US National Cancer Institute lists chronic H. pylori infection as a major risk factor for cancer in the lower and middle stomach, and obesity and reflux as raising the risk of cancer in the upper stomach. Other risk factors include chronic atrophic gastritis, intestinal metaplasia, pernicious anemia, a first-degree relative with stomach cancer, inherited syndromes such as hereditary diffuse gastric cancer, smoking, and a diet low in fruit and vegetables or high in salted, smoked or poorly preserved foods. It notes that treating H. pylori reduces the risk, that smoking makes that treatment less effective, and that smokers who stop lower their risk over time, NCI, stomach cancer causes and risk factors. ↩
11. On risk and treatment: NHS guidance advises stopping smoking, losing weight if overweight, eating less salt and eating at least five portions of fruit and vegetables a day. Treatment depends on the type and size of the cancer, where it is, whether it has spread and general health, and usually includes surgery, which removes part or all of the stomach, and chemotherapy, often before and after the operation. Recovery from surgery can take a long time, and checkups continue during and after treatment. Where the cancer cannot be removed, treatment aims to limit it and its symptoms and help people live longer, with a palliative care team, NHS, stomach cancer treatment. ↩
12. ToGA trial: Bang YJ, et al. Trastuzumab in combination with chemotherapy for HER2-⁠positive advanced gastric cancer. Lancet. 2010;376:687-⁠697. PubMed 20728210. Roughly 15 to 20% of gastric cancers are HER2-⁠positive, and adding trastuzumab improved survival in that group. HER2 testing is therefore standard in advanced disease. ↩
13. On immunotherapy for advanced HER2-⁠negative gastric cancer: in a phase 3 trial of 1,581 previously untreated patients, adding nivolumab to fluoropyrimidine and oxaliplatin chemotherapy improved overall survival in tumors with a PD-L1 combined positive score of 5 or more, and also in those with a score of 1 or more, PubMed 34102137. A second trial of 1,579 patients found that adding pembrolizumab to chemotherapy lengthened median survival from 11.5 to 12.9 months overall, and from 11.4 to 13.0 months with a score of 1 or higher, PubMed 37875143. The US labels for both drugs limit this use to tumors that express PD-L1 with a score of 1 or higher, FDA nivolumab prescribing information, 2025, DailyMed pembrolizumab label, 2026. ↩
14. On post-gastrectomy nutrition: total or partial gastrectomy causes loss of intrinsic factor and reduced gastric acid, so vitamin B12 requires lifelong replacement (often by injection) and iron and calcium absorption fall. Exocrine pancreatic insufficiency is also common after gastrectomy because food and pancreatic enzymes no longer arrive in the duodenum together. Dumping syndrome affects a substantial minority. This is specialist dietetic territory. ↩
15. On garlic and antioxidant supplements: in a randomized trial of 3,365 residents of a high-risk region of China, followed for 22 years, garlic supplements taken for 7.3 years did not significantly lower gastric cancer incidence, though gastric cancer deaths were lower, while a combination of vitamin C, vitamin E and selenium lowered both, PubMed 31511230. Across 20 randomized trials, a Cochrane review found no convincing evidence that antioxidant supplements prevent digestive cancers, and some combinations raised overall mortality, PubMed 18677777. ↩
16. On salt and preserved foods: World Cancer Research Fund / AICR Continuous Update Project. wcrf.org. Salt-preserved foods are judged a probable cause of stomach cancer, and the highest-incidence regions historically had the highest intakes. The under-⁠5 g/day salt figure on this page is the general population target, not a cancer-specific dose. ↩
17. FLOT4: Al-Batran SE, et al. Perioperative chemotherapy with fluorouracil plus leucovorin, oxaliplatin, and docetaxel versus fluorouracil or capecitabine plus cisplatin and epirubicin. Lancet. 2019;393:1948-⁠1957. PubMed 30982686. Basis for perioperative FLOT over ECF/ECX in locally advanced resectable disease. The trial gave four 2-⁠week cycles of FLOT before surgery and four after, against three 3-⁠week cycles of ECF/ECX before and three after. That is a comparison between two chemotherapy regimens. ↩
18. On ultra-processed food: in a French cohort of 104,980 adults, each 10% increase in the share of ultra-processed food in the diet was associated with about 12% higher overall cancer risk and 11% higher breast cancer risk, after adjusting for known risk factors. This is an observational association, PubMed 29444771. ↩
19. On antioxidant supplements during cancer treatment: the US National Cancer Institute notes that randomized trials have had mixed results, that some found worse outcomes in people who took antioxidant supplements during cancer therapy, especially smokers, and that people with cancer should tell their doctors about any dietary supplement they use, NCI, antioxidants and cancer prevention. ↩
20. On omega-⁠3 for weight and muscle loss in cancer: a Cochrane review of five trials with 587 patients found insufficient data to establish whether oral EPA was better than placebo, PubMed 17253515. ↩
21. Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of long-term marine omega-⁠3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021;144(25):1981-⁠1990. PubMed 34612056. Seven trials with 81,210 people followed for about 5 years: omega-⁠3 supplements were linked to a higher risk of atrial fibrillation (hazard ratio 1.25), more so in trials of more than 1 g a day (1.49), and the risk rose with each additional gram. ↩
22. On probiotics with H. pylori treatment: a meta-analysis of 13 randomized trials in 2,306 patients found that probiotics added to prescribed eradication therapy lowered antibiotic side effects such as nausea, vomiting and diarrhea, with differences between trials. Probiotics were studied as an add-on to the antibiotic course, not in place of it, PubMed 27723762. ↩
23. On treatment by stage: the US National Cancer Institute describes endoscopic resection for very early cancer confined to the stomach lining, gastrectomy as the main operation, and chemotherapy given before surgery to shrink the tumor or after it to lower the risk of the cancer coming back, NCI, stomach cancer treatment. ↩
24. On dumping syndrome: NIH guidance notes that it is more common after a gastrectomy that removes the whole stomach than after one that removes part of it, and that treatment starts with changing how and what you eat, such as six small meals a day instead of three larger ones, waiting to drink liquids until at least 30 minutes after a meal, and lying down for 30 minutes after eating, NIDDK, dumping syndrome. ↩
25. On vitamin B12 after gastrectomy: a meta-analysis of 14 studies with 2,627 people who had surgery for gastric cancer found vitamin B12 deficiency in about 49%, with anemia, tiredness, numbness and dizziness among the symptoms, PubMed 37669168. ↩
26. On fever during chemotherapy: NHS guidance says to call your care team right away for a high temperature, feeling hot, cold, sweaty or shivery, or other signs of infection, and for pain, swelling and warmth in a leg or arm or sudden breathlessness, which can be signs of a blood clot. The US National Cancer Institute lists a fever of 100.5°F (38°C) or higher as a sign of infection and says infections during cancer treatment can be life-threatening and need urgent medical attention, NHS, chemotherapy side effects, NCI, infection during cancer treatment. ↩
27. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩