Guide

The thing that surprises people about being ill with diabetes is that blood sugar often goes up while food intake goes down.

Infection triggers cortisol, adrenaline and other counter-regulatory hormones. Those raise glucose production in the liver and make cells less responsive to insulin at the same time. So a day of dry toast and no appetite can still produce readings well above normal.

This piece is about principles and preparation. The specific numbers for your sick-day plan — insulin adjustments, when to call — should come from your care team, and the best time to get them is while you're well.

The rules that matter most

Never stop insulin. This is the one that causes the most harm. If you have type 1 and you stop basal insulin because you aren't eating, you're on a path toward diabetic ketoacidosis, and illness is already pushing you that way. Insulin needs frequently go up during illness, not down.

Test more often. Every two to four hours, including overnight, rather than the usual schedule.

Check ketones if you have type 1 and your glucose is running high — commonly above about 250 mg/dL (14 mmol/L) — or if you're vomiting at any glucose level. Blood ketone meters are more reliable than urine strips.

Keep fluids going. Dehydration concentrates blood glucose and accelerates everything else that's going wrong. Roughly a cup an hour is the usual target.

The one time fast carbohydrate is the right answer

Everything on this site argues for slowing carbohydrate absorption down. Sick-day guidance inverts that, and it's worth understanding why.

If you can't keep food down but your medication is still working, you need carbohydrate in a form that's easy to absorb and easy to keep down. The standard guidance is roughly 15 grams of carbohydrate every hour while you're unable to eat normally.

Things that deliver it: regular (not diet) soda, fruit juice, sports drinks, ice lollies, honey, jelly, regular gelatin desserts, sweetened tea.

If your glucose is running high, switch to sugar-free fluids — water, broth, sugar-free electrolyte drinks — and keep the volume up.

When you can eat a little

Small amounts, frequently, of things that are easy on the stomach and predictable in carbohydrate:

• Broth or clear soup, which also replaces sodium
• Plain crackers or dry toast
• Plain rice or congee
• Banana or apple sauce
• Yogurt, if dairy is tolerated
• Scrambled egg, once solid food is going down

Salt matters more than usual if you've been vomiting or have diarrhoea. Broth, salted crackers and oral rehydration solutions all address it.

Medications that should pause when you're dehydrated

Several common medications become riskier during illness with vomiting, diarrhoea, or reduced fluid intake, and many diabetes services teach a specific list to hold temporarily.

The categories usually named are metformin, SGLT2 inhibitors, sulfonylureas, ACE inhibitors, ARBs, diuretics, and NSAIDs. The reasons vary — metformin plus dehydration raises the risk of lactic acidosis; diuretics and ACE inhibitors stress the kidneys further; sulfonylureas can cause lows if you aren't eating.

SGLT2 inhibitors deserve their own line. They can cause diabetic ketoacidosis at normal or near-normal glucose levels, which means the usual warning sign is absent. If you take one and you're unwell, ketone testing matters even when your readings look fine.

Insulin is not on the hold list. It stays.

Get your own version of this list from your prescriber, because it depends on what you actually take.

When to call for help

Contact your care team or seek urgent care if:

• You can't keep fluids down for more than a few hours
• Ketones are moderate or large, or rising
• Blood glucose stays high despite correction doses
• You have breathing difficulty, confusion, or breath that smells fruity
• Vomiting and diarrhoea continue beyond about six hours
• You're unsure — which is a legitimate reason on its own

Diabetic ketoacidosis develops over hours, not days, and it's considerably easier to treat early.

Build the kit while you're well

Nobody assembles this at 3 a.m. with a fever. A box in the cupboard with:

• Ketone test strips, in date — check them, they expire
• Regular soda or juice boxes, and sugar-free electrolyte sachets
• Broth or stock cubes, plain crackers
• Paracetamol, and anti-nausea medication if you've been prescribed it
• A written copy of your sick-day plan, including who to call
• Spare insulin and pen needles or pump supplies

Check the strips and the plan once a year, roughly when you check the smoke alarm.

Vomiting, and the 15-minute rule

Keeping fluid down when your stomach is rejecting everything is its own skill, and volume is usually the problem.

Small sips at short intervals work where a glass doesn't — a tablespoon or two every ten to fifteen minutes, built up gradually if it stays down. Ice chips and frozen juice lollies are often tolerated when liquid isn't, because they arrive slowly by design.

If nothing stays down for more than a couple of hours, that's the point to stop experimenting and call. Dehydration plus diabetes moves quickly, and intravenous fluids are a straightforward fix that's much easier applied early.

What glycemic load has to do with it

Almost nothing, for two or three days, and that's the point worth making.

Sick-day eating is a different task with different rules: keep glucose from going too high or too low, keep fluids in, avoid ketones. Refined carbohydrate you'd avoid on an ordinary Tuesday is a tool here.

Normal eating resumes when you're well. A few days of white toast and flat lemonade during flu will not undo anything, and treating the sick-day plan as a failure of discipline is how people end up making the actual dangerous choice, which is skipping insulin because they didn't eat.