What each part of a meal does to blood sugar

There is no list of banned foods in type 1 diabetes. What helps instead is a simple picture of what each part of a meal does to blood sugar, and how fast. This page sets out that picture, shows where carbohydrate tends to hide, and explains which foods need no insulin dose at all, along with the catch that comes with them.

Four parts of a meal, fastest to slowest

Think of a plate as four ingredients, lined up from fastest to slowest. That ordering is the mental model everything else in this section builds on.

Protein: slow and modest. Protein causes a meaningful rise only when there's a lot of it, and that rise arrives roughly three to five hours later. A normal portion alongside carbs needs no separate dose.

Fat: no direct rise, but a long shadow. Fat doesn't raise blood sugar directly. It slows the whole meal down and makes insulin work less well for hours. That is why the late rise after a rich meal catches people out; it has its own page.

Fibre: counted, then subtracted. Fibre is counted as carbohydrate on the label, but your body doesn't absorb it, so you subtract it back out. It also slows everything around it down, which flattens the peak.

Where the carbohydrate actually hides

Bread and sugar are obvious. These are the ones that catch newly diagnosed people and well-meaning hosts. Ask a host which of these five are in tonight's meal: usually it's three, and usually none of them were mentioned.

• Starchy vegetables. Potatoes, corn and green peas are carbohydrate, not free vegetables. "It's a vegetable" is the single most common counting error.
• Milk and yoghurt. Dairy carries natural sugar. A glass of milk is a dose, even unsweetened and even when nothing tastes sweet.
• Beans and lentils. Filed mentally as protein, counted as carbohydrate. They're high in fibre, so they come on slowly, but they come.
• Juice and smoothies. Fruit with the fibre removed and the speed turned up. Excellent for treating a low, awkward as a drink with dinner.
• Sauces and dressings. Barbecue sauce, ketchup, teriyaki, sweet chilli and most jarred pasta sauces are sugar-heavy. Nobody counts the glaze.

Foods that need no dose at all

Some foods carry essentially no carbohydrate:

• meat, poultry, fish and eggs
• shellfish
• most cheeses
• tofu
• fats and oils
• herbs, spices and condiments
• tea, coffee and diet drinks
• clear broths
• plain unsweetened gelatin

Salad greens and most non-starchy vegetables are close enough to free that they're treated that way.

Diet drinks belong on this list, which also means they are useless for treating a low. That point comes up again on the page about lows, alcohol and sick days.

This apparent contradiction confuses newly diagnosed people constantly. If a carb-free dinner is followed by a higher number later in the evening, nothing was counted wrong: the protein and fat were simply doing their slow work. Bring patterns like this to your diabetes team or dietitian rather than adjusting on your own.