doctor assisting patient with gi cancers

Malnutrition and GI Cancers

Rosanna Lee, RD

Written by: Rosanna Lee, RD

Updated: November 21st, 2023

Gastrointestinal cancers can significantly increase the risk for malnutrition, due to a variety of factors. The impact on nutritional status is often determined by the site of the cancer. Additionally, treatments for cancer including chemotherapy and radiation can impact food taste and palatability, and can be associated with nausea and changes in appetite. Below, we’ve outlined three common GI cancers and how each can impact nutritional status.

Colorectal Cancer

In 2022, it was estimated that 24,300 Canadians would be diagnosed with colorectal cancer, and that 9,400 Canadians would die from this disease. Regular screening is often recommended for early detection and treatment. In Canada, the protocol for screening is to perform a stool test in all average risk (ie. no family history) individual’s ages 50-74 every 2 years. Additionally, those who have increased risk of developing colorectal cancer due to family history are recommended to be screened every 5-10 years via colonoscopy starting at age 50.

Colorectal cancer starts with an abnormal cell growth occurring in the colon or rectum. This type of cancer often beginning as a an abnormal growth of tissue called a polyp. Individuals may or may not have symptoms of colorectal cancer. Those who do experience symptoms may note changes in their bowel routine, blood in their stools, diarrhea, constipation, incomplete bowel emptying, gas, nausea, vomiting, fatigue/ weakness, anemia, loss of appetite, unexplained weight loss, bowel obstruction, swollen lymph nodes, enlarged liver, jaundice, ascites, and even breathing problems. Pain or cramping in the abdomen, back, buttocks, or legs is often reported as well.

While the colon has many roles in digestion, it is important for stool formation, as well as fluid and electrolyte absorption. Therefore, cancer in this area can impact fluid and electrolyte absorption (potassium, magnesium, sodium, calcium are all example of electrolytes). Gut bacteria in the colon also help with breaking down carbohydrates that remain after the beginning stages of digestion. Colorectal cancer may impair this carbohydrate breakdown, which can also reduce the production of some B and K vitamins as a byproduct.

Chemotherapy, radiation therapy, and/or bowel surgery may be used for treatment but often result in side effects that impact food tolerance and digestion. Post-surgical nutrition often involves a lower residue diet for a short period of time to allow tissue healing, however this is not generally a long-term approach. With chemotherapy, patients may have difficulty tolerating food due to nausea, vomiting, loss of appetite, changes to taste and smell, diarrhea, constipation, and, or mucositis. Most times, the focus in these patients is on a high calorie and high protein diet of bland/minimally seasoned foods, to prevent malnutrition and address food aversions. Adequate hydration is also a key pillar.

Radiation therapy may cause irritation in the rectum and even cause diarrhea as well; therefore, individuals may also be recommended a low residue diet to lessen irritation. Oral nutrition supplements, oral rehydration solutions, and multivitamins may be used to supplement nutritional needs if intake is inadequate to reduce malnutrition. To lessen the risk of colorectal cancer, reduce alcohol intake, quit smoking, increase physical activity, and improve your intake of dietary fiber from foods such as vegetables, fruit, pulses, and whole grains.

Esophageal Cancer

Esophageal cancer is the sixth leading cause of cancer-related death worldwide. Cancer in the esophageal area can exist anywhere between your throat and your stomach. Unfortunately, this type of cancer can really limit the movement of food to the other parts of your digestive tract. Symptoms like dysphagia, coughing, hoarseness in the throat, indigestion, heartburn, chest pain/ pressure and burning sensations can occur.  This frequently results in undereating, malnutrition, and unintentional weight loss, especially if untreated. Nutrition interventions for those with esophageal cancer often involve liquids,  thin pureed foods, or soft foods in order to allow food to travel through the narrowed esophageal opening. Some patients also experience changes in the contractions (peristalsis) in their esophagus, making it difficult to move foods that are thick, crunchy, or chunky – another reason why thin, soft foods or liquids are often recommended.

There are different types of esophageal cancer that are classified based on the type of cells that grow. Adenocarcinoma is one type of esophageal cancer that starts in the cells of the mucus glands in the esophagus and usually resides in the lower part of the esophagus, right before the stomach. Another type, called squamous cell carcinoma can also grow in the esophagus but looks a bit different. These cancer cells are flat and thin. This type of cancer is often found in the upper and middle portions of the esophagus. While there are other types of esophageal cancer, these are the 2 most common.

Risk factors for esophageal cancer include smoking, excess alcohol intake or hot beverage intake, being obese, chronic heartburn or acid reflux/GERD, Barrett’s esophagus (possibly from chronic GERD), and achalasia. Treatments may involve radiation therapy, chemotherapy, and/or surgery. Integrating a healthy diet with a variety of vegetables and fruits, maintaining a healthy weight, and avoiding/ lessening tobacco and alcohol intake can help with risk reduction.  

Gastric Cancer

Gastric or stomach cancer can occur in any of the five regions of the stomach: cardia, fundus, body, antrum, or pylorus. There are several types of stomach cancers, including adenocarcinoma (starts in mucosal cells), gastrointestinal stromal tumors (starts in nerve cells in the wall of the stomach), carcinoid tumors (starts in the neuroendocrine cells), and lymphoma (starts in immune cells in the stomach).

The stomach’s primary role in digestion is to both mechanically and chemically break down food. It uses contractions and movement to grind and mash food, while also using enzymes and stomach acid to aid in the breakdown process. Therefore, symptoms of gastric cancer effect the stomach’s ability to properly perform these tasks. Common symptoms are difficulty swallowing, belly pain, bloating, early satiety, poor appetite, heartburn, indigestion, nausea, vomiting, unintentional weight loss, fatigue, and black or tarry stools.

Although the cause of stomach cancer is not yet known, we do know that dietary and lifestyle factors impact risk. High consumption of smoked or salted foods, processed meats, alcohol, and smoking increase gastric cancer risk. One primary theory is that stomach cancer risk increases when the cells lining the stomach have been damaged or inflamed. For instance, helicobacter pylori (H. pylori) bacteria can impact the inner lining of the stomach, as well as chronic acid reflux. However, we still have lots to learn!

Treatment options for gastric cancer like surgery and chemotherapy can impair vitamin B12 levels due to alterations in the stomach’s ability to produce intrinsic factor, a protein that helps the body absorb vitamin B12. Surgical treatments like gastrectomy can also impair iron levels because the stomach is responsible for acid production, which also supports iron uptake. As such, lower vitamin B12 and iron levels could lead to anemia. Lower calcium levels are also another concern and could be caused by dumping syndrome (when stomach contents are emptied into the intestines too quickly) as a side effect of stomach resectioning or poor calcium intake. Other deficiencies can result from poor intake in general, due to nausea, vomiting, or loss of appetite from gastric cancer symptoms, or from the side effects of treatment (i.e., chemotherapy and radiation). Additionally, changes to the stomach can impact the levels of stomach acid and enzymatic production that help with the chemical breakdown of food. There could also be impairments to the stomach’s ability to mechanically mix foods with these digestive juices.

A regular, healthy diet may not provide enough calories, macro-and micronutrients due to limited or impaired absorption. Therefore, a multivitamin and/or oral nutrition supplementation are often included as part of treatment to prevent deficiencies and malnutrition. Oral rehydration solutions (ORS) may also be used to treat dehydration should there be prolonged symptoms of vomiting and/or diarrhea from cancer treatment. ORS can help replete fluid, electrolytes (sodium, potassium), and glucose levels back to baseline.

Overall, maintaining a healthy diet and engaging in beneficial lifestyle practices are key to reducing the risk for gastrointestinal cancers. Routine check-ups with your family doctor are advised if you have a known family history, a genetic predisposition, and if you are over 60 and a male.


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