Managing diabetes normally means eating consistently. Cancer treatment means nothing is consistent, appetite disappears, food tastes like metal, your mouth hurts, and then a steroid dose sends your glucose to numbers you have not seen in years.
Both things are true at once. Here is how to hold them together.
During treatment, losing muscle is a bigger threat than a temporarily higher A1C. If you have to choose between eating something and eating nothing, eat something. Then tell your team so the plan can adapt.
The priority order changes
Outside treatment, the goal is stable glucose. During treatment, the order is usually:
- Enough calories and protein to hold your weight and muscle. Muscle loss predicts worse chemotherapy tolerance, more dose reductions and worse outcomes.
- Managing the symptom in front of you, nausea, mouth sores, taste change, diarrhoea, constipation.
- Hydration.
- Glucose control, adjusted to the new reality rather than the old target.
Your oncology team may loosen your glucose targets during treatment on purpose. That is a clinical decision, not a failure.
Protein first, always
Many people in treatment need roughly 1.0–1.5 g of protein per kilogram of body weight daily, often well above what they ate before, at exactly the moment eating is hardest.
Protein sources that survive a bad appetite day and are kind to glucose:
- Greek yogurt or skyr, plain, with a little fruit
- Eggs in any form, scrambled soft when the mouth is sore
- Cottage cheese, blended smooth if texture is a problem
- Shredded chicken or fish in broth
- Silken tofu blended into soups or smoothies
- Unsweetened protein powder stirred into soup, oatmeal or milk
- Lentil or bean soup, blended if chewing is difficult
- Nut butters, if the mouth is not sore
Ask specifically for an oncology dietitian. This is a real specialty, usually covered, and consistently underused.
Managing the symptom in front of you
Nausea. Small amounts every two hours beats three meals. Cold or room-temperature food smells less. Dry, plain starches early in the day. Ginger tea or chews as an adjunct to your prescribed antiemetics, take those on schedule rather than waiting for the nausea to arrive.
Metallic taste. Plastic utensils instead of metal. More acid: lemon, vinegar, pickles, unless your mouth is sore. Marinate proteins. Cold foods taste less metallic. Rinse with a baking-soda and salt solution before eating.
Mouth sores. Soft, bland, room temperature. Avoid acid, spice, crunch and alcohol-based mouthwash. Blend soups and smoothies. Cold things numb. Ask about medicated mouth rinses, do not just endure it.
Diarrhoea. Soluble fibre helps: oats, bananas, white rice, applesauce. Hydrate with electrolytes, not plain water alone. Watch for hypoglycaemia if you take insulin or sulfonylureas and are absorbing less.
Constipation. Common with antiemetics and opioids. Fluid, gentle movement, soluble fibre, and ask for a bowel regimen upfront rather than after three miserable days.
No appetite at all. Set alarms and eat by the clock, not by hunger. Make every mouthful count, fortify milk with skimmed milk powder, add olive oil or nut butter to soft foods. Keep something drinkable within arm's reach.
Steroid days
Dexamethasone and prednisone are routine in many protocols, and they will raise your blood glucose, often sharply, often for two to four days after each dose, and typically worst in the afternoon and evening.
Plan for it:
- Ask your diabetes team for a written steroid-day plan before cycle one, including whether your medication changes on those days.
- Test more often on steroid days, this is where continuous glucose monitoring earns its keep.
- Front-load protein and vegetables; steroids also drive appetite and cravings.
- Expect the pattern to repeat with each cycle, and log it so the pattern is visible rather than surprising.
- Know your team's threshold for calling. Very high readings with thirst, frequent urination or confusion need a phone call, not a wait-and-see.
Food safety when counts are low
During neutropenia, ordinary food risks become real risks:
- No raw or undercooked eggs, meat, fish or shellfish
- No unpasteurised dairy, juice or soft cheeses
- Wash produce thoroughly; peel where practical
- Avoid buffets, salad bars and deli counters
- Reheat leftovers thoroughly and discard after 48 hours
- Skip probiotic supplements unless your team approves them
What to skip
Extreme diets. Ketogenic, fasting-mimicking, juice-only and "alkaline" protocols during active treatment are, at best, unproven and, at worst, cause the weight and muscle loss that predicts worse outcomes. If you want to try something studied, ask about enrolling in a trial rather than improvising.
Cutting all sugar to "starve" the tumour. It does not work that way, and the collateral damage is real. Long-term metabolic health matters; short-term self-starvation during chemotherapy does not.
Unvetted supplements. See the interaction guide, several common ones interfere with treatment.
Frequently asked questions
My A1C has gone up since treatment started. Have I failed?
No. Steroids, reduced activity, changed eating and stress all push glucose up during treatment. This is expected. The job now is to avoid extremes and dangerous lows, keep your weight and muscle, and get back to your usual targets once treatment ends.
Can I use meal-replacement shakes?
Often yes, and they are genuinely useful on bad days. Choose lower-sugar, higher-protein formulations, and ask your dietitian which product suits both your treatment and your diabetes, several are made specifically for this situation.
Should I take probiotics?
Not without approval. During immunosuppression, live-culture supplements carry a real infection risk. Yogurt may be fine when counts are normal; concentrated supplements need clearance.
I have lost 5 kg without trying. Is that a problem?
Yes, tell your team now, even if the weight loss feels welcome. Unintentional loss during treatment predicts worse tolerance, and there are interventions, including appetite support and nutrition supplementation, that work better early.
Educational content only, not medical advice. Nutrition during cancer treatment should be individualised with your oncology team and a registered dietitian.