Carbohydrate counting and boluses

Food is the part of pump therapy that people most often ask about, and carbohydrate counting is the skill behind it. The idea is simple to state: carbohydrate in a meal raises glucose, so the mealtime insulin is matched to the amount eaten. Doing it well is a learned skill, taught by health professionals, and the numbers involved are personal. This page therefore explains the concepts and the UK guidance around them, and deliberately gives no ratios or doses. Those are set by each person's diabetes team.

What carbohydrate counting is

Carbohydrate counting means working out how much carbohydrate is in food and drink so that insulin can be matched to it. Diabetes UK says that people with type 1 diabetes, and some people with other types, may count carbohydrate as an effective way of managing blood sugar levels, and that it is particularly helpful if you use basal and bolus insulin. It adds that carbs can be counted in grams or as portions, with one portion usually equal to 10 g of carbohydrate, and that the total carbohydrate on a label is what matters rather than the "of which sugars" line.

Diabetes UK is also frank that learning takes time and effort, and that carb counting does not mean total freedom. What it can offer, once learned, is more flexibility in when and what a person eats.

Why it is used with pumps

A pump gives a steady background supply of insulin, so mealtime insulin comes from boluses, the extra amounts a person tells the pump to deliver. The full picture is on how an insulin pump works. Diabetes UK explains that most pumps have a bolus calculator: you enter how many carbs you are going to eat and your blood sugar level, and the pump does the maths. For corrections, the calculator also takes into account insulin on board, a concept described in the entry for active insulin.

A calculator is only as good as what it is given. If the carbohydrate estimate is off, the suggested bolus is off too. A Cambridge University Hospitals leaflet on fat and protein bolusing, written for adults, asks readers to check first whether their carbohydrate counting is accurate, and says it is unsafe for people who do not count accurately to use the advice in that leaflet.

The carbohydrate ratio in concept

The link between carbohydrate and insulin is the carbohydrate ratio, sometimes called the insulin-to-carbohydrate ratio. Diabetes UK says these ratios are different from person to person, depending on factors like age, weight, activity levels and how sensitive someone is to insulin. The diabetes healthcare team helps to work the ratio out, usually estimating a starting point and then fine-tuning it using blood sugar levels, and a person may eventually have a different ratio for each meal. Diabetes UK adds that the amount actually taken also depends on other factors such as current blood sugar, illness or exercise.

Because the ratio is individual, no figure appears here. Related settings, such as the insulin sensitivity factor used for corrections, are likewise programmed with the team. On exercise, see exercise and insulin pumps.

Pre-bolusing

A pre-bolus is a bolus given before the food rather than at the first mouthful. One of the opened sources covers timing. The Cambridge University Hospitals leaflet says that, whenever possible, a bolus for a high-fat or high-protein meal is given 15 minutes before eating, and describes what to do if that is not possible and glucose is already above target. It is written for adults, and the leaflet states that its advice is not intended for people using hybrid closed loop systems and has not been tested in them. Whether and how to pre-bolus is something to settle with the team.

Extended and dual boluses

A standard bolus delivers its insulin all at once. An extended bolus spreads delivery over a period, and a dual bolus gives some immediately and the rest over time. The same Cambridge leaflet explains why this can matter: carbohydrate in a high-fat or high-protein meal is digested and absorbed more slowly, so glucose can stay higher for longer, and protein can cause a delayed rise. It lists problematic meals such as takeaways and pies, and notes that manufacturers use different names for a dual bolus, including "dual wave", "extended" and "combination" bolus. The leaflet also says that working out an add-on bolus for fat and protein can take far longer than getting carbohydrate doses right, and advises patience. The extra insulin and the split that suit one person will not suit another, which is why this page stops at the concept and does not offer percentages.

Structured education and DAFNE

NICE recommends that adults with type 1 diabetes are offered a structured education programme of proven benefit, giving the DAFNE (dose adjustment for normal eating) programme as an example. NICE's adult guideline NG17 also recommends offering carbohydrate-counting training as part of structured education programmes, and considering carbohydrate-counting courses for people waiting for a more detailed programme or unable to take part in a standalone one. See DAFNE in the glossary for the short definition.

The DAFNE website says that DAFNE stands for Dose Adjustment For Normal Eating and aims to help people aged 17 and over with type 1 diabetes lead as normal a life as possible, while maintaining blood glucose levels within healthy targets to reduce the risk of long-term complications.

The diabetes team and the dietitian

NICE's technology appraisal TA151 says pump therapy should be started by a specialist team that should normally include a physician, a diabetes specialist nurse and a dietitian, and that the team should provide structured education and advice on diet, lifestyle and exercise. Diabetes UK says that to count carbohydrate successfully people need the support of professionals, either their diabetes healthcare team or a structured education course, and that the team can say which courses are available locally. Whether a course is run in groups, online or one to one varies, and the team will know what is on offer. Wider questions about illness are on the sick days with a pump page.

In short

Carbohydrate counting matches mealtime insulin to the food eaten, and a pump's bolus calculator does the arithmetic once the carbohydrate has been estimated and the personal ratio set. Features such as pre-bolusing and extended boluses exist for particular meals, but their settings are individual. Structured education, the diabetes specialist nurse and the dietitian are the routes to learning the skill safely.