Eating when radiation is aimed near your digestive tract

A radiation beam aimed at a tumour in the abdomen or pelvis has to travel through whatever else is in the way. NCI puts it directly: radiation damages healthy tissue when directed at the abdomen, pelvis or rectum, and diarrhoea can follow.

The bowel lining is made of cells that renew themselves quickly, which is precisely the sort of tissue radiation affects most. That is not a sign the treatment is going wrong. It is a known trade-off, and it is temporary for most people.

What you eat will not change the radiation, but it can change how rough the weeks feel.

NCI's management advice starts with drinking, not eating.

The suggestion is clear liquids such as water and broth, taken at room temperature. Room temperature is a small detail that people skip, and it is easier on an irritated gut than something very cold or very hot.

The reason fluids lead the list is that NCI describes severe diarrhoea as risking dehydration, and describes dehydration as life threatening. Keeping fluid going in is the part that matters most.

Two changes to how you eat appear in NCI's advice: smaller portions, and more often.

Small frequent meals put less through the system at once. On days when appetite is poor anyway, they are also simply more achievable than three full plates.

Low fibre is the other half of it. Fibre is normally good advice, and during treatment-related diarrhoea it is the opposite, because it adds bulk and residue to a bowel that is already struggling.

Diarrhoea takes minerals out along with fluid. NCI suggests eating foods with sodium and potassium, giving potatoes, bananas and broth as its examples.

Broth appears twice in NCI's guidance, as a clear liquid and as a source of sodium, which makes it a particularly practical thing to have in the cupboard during a course of radiation.

NCI lists foods and drinks that can make diarrhoea worse.

• Alcohol
• Milk and dairy products
• Spicy foods
• Caffeinated drinks
• Dried beans
• Foods high in fat
• Fruit juices
• Sugar-free gum or sweets

Fat and spice are the ones people notice most quickly. Dairy surprises some, and it may only be a temporary restriction, so it is worth asking your team when to reintroduce things.

None of this is meant as a permanent way of eating. It is a temporary adjustment for a temporary problem.

NCI includes one piece of practical advice that has nothing to do with food: keep the anal area clean using warm water.

Frequent bowel movements make the skin there sore quickly, and soreness is often what tips a manageable week into a miserable one. Gentle cleaning, and mentioning it if the skin breaks down, are both worth doing early.

Dietary measures cover the milder end. NCI describes grades 1 and 2 diarrhoea, meaning up to six bowel movements above your normal daily number, as usually manageable at home, and says grades 3 and 4 can be life threatening.

Report fever, dizziness, weight loss or blood in stools to your team, whatever your food intake looks like. NCI names all of those among the symptoms to report.

Radiation courses run for weeks, and eating well through them affects how you tolerate the rest of treatment. Many cancer services have a dietitian, and a referral is a reasonable thing to request rather than wait for.

Bring a few days of notes on what you have eaten and how your bowel responded. That turns a vague conversation into a specific one.

• Call your care team the same day if you are having seven or more bowel movements above your normal daily number. NCI puts that in grades 3 and 4, which it describes as possibly life threatening and sometimes needing hospital treatment.
• Call your care team the same day if you feel dizzy, run a fever, or see blood or mucus in your stools. NCI names all of these among the things to report.
• Call your care team within a day or two if you are losing weight, or if the diarrhoea is not settling on the food and fluid changes above. NCI asks people to tell the team about diarrhoea because dehydration can be life threatening.