The basic principle of intensified conventional insulin therapy
The basic principle of intensified conventional insulin therapy is that a varying amount of short-acting insulin is injected with the main meals — depending on the blood glucose level and the meal. A basal insulin covers the basic insulin requirement, which is independent of meals.
This therapy is characterized by the fact that it is based on the body’s natural physiological conditions. Compared with conventional therapy (CT), it generally offers:
• a significantly better regulation of blood glucose levels,
• a markedly reduced risk of developing diabetic complications [1],
• considerably greater flexibility with regard to diet and daily routine,
• the possibility to skip or vary meals,
• the ability to influence blood glucose levels precisely through insulin,
• the requirement of self-monitoring of blood glucose (SMBG) or continuous glucose monitoring (CGM) to fully utilize the therapeutic potential of ICT,
• the necessity of comprehensive, structured education to enable patients to make full use of the therapy’s possibilities.
T1D 5: Insulin Action Profile in Intensified Conventional Insulin Therapy (ICT)
In this form of therapy, short-acting insulin is injected at mealtimes. The basal insulin requirement, which is independent of food intake, is covered by a long-acting (basal) insulin.
(The blue curve in the background of the graph represents insulin levels in people without diabetes.)
Intensified Insulin Therapy — The Standard for Type 1 Diabetes
Today, intensified insulin therapy is the standard of care for type 1 diabetes. It achieves clearly better treatment outcomes and improves quality of life compared to conventional therapy (CT) [1].
Essential Requirement for Successful ICT: Patient Education
Performing ICT successfully requires structured diabetes education. Without thorough instruction, ICT will fail.
Structured, evidence-based education programs are available and are typically conducted in specialized diabetes centers.
Anyone who injects insulin but refuses training risks serious harm.
Carbohydrate Counting
To perform ICT correctly, patients must learn to estimate the amount of carbohydrates in their meals, since the insulin dose is based on this.
In Germany, carbohydrate portions were historically expressed as bread units (BU) or carbohydrate units (CU), but internationally this is replaced by counting grams of carbohydrate (g CHO).
1 BU ≈ 12 g carbohydrate
1 CU ≈ 10 g carbohydrate
Therefore, insulin dosing is now based on grams of carbohydrate using an insulin-to-carbohydrate ratio (ICR) — that is, how many grams of carbohydrate are covered by 1 unit of insulin.
At first, it’s advisable to weigh food to learn accurate carbohydrate estimation. Later, this becomes intuitive. Since carbohydrate counts are always estimates, small deviations are normal.
How Much Insulin Is Injected for Meals?
The meal insulin dose (bolus) consists of:
Additional factors — such as planned physical activity, fat and protein content of meals, illness, medications (e.g., corticosteroids), or hormonal changes (e.g., menstrual cycle) — can also affect insulin requirements and must be considered when calculating the bolus and basal doses.
The Insulin-to-Carbohydrate Ratio (ICR)
The ICR describes how many grams of carbohydrate are covered by 1 unit of insulin.
This ratio is individual and may vary by time of day.
Typical starting values for people with type 1 diabetes:
Example:
If the ICR is 1 unit per 10 g CHO, and a person eats 40 g CHO, they inject 4 units of insulin.
Before injection, blood glucose must be measured:
Calculating Correction Doses
Each patient should know their correction factor (Insulin Sensitivity Factor, ISF) — how much one unit of insulin lowers blood glucose.
For many people, 1 unit lowers blood glucose by about 30 mg/dl (1.6 mmol/l).
Example:
Target glucose = 120 mg/dl (6.6 mmol/l)
Correction factor = 1 unit → 30 mg/dl (1.6 mmol/l) drop
Formula:
Meal insulin = (Total grams of carbohydrate ÷ ICR) + Correction dose
Example:
Meal contains 48 g CHO, ICR = 1:12 → 4 units insulin
Current glucose = 180 mg/dl, target = 120 mg/dl → correction = 2 units
→ Total = 6 units insulin
Carbohydrates have the most immediate effect on blood glucose, but fat and protein can also raise glucose levels hours later.
This is due to:
Calculating FPUs
One FPU corresponds to 100 kcal from fat and protein
(1 g fat = 9 kcal; 1 g protein = 4 kcal).
Because the glucose-raising effect is delayed, the insulin for FPU coverage should be given later, typically 2–4 hours after the meal.
Under ICT (without a pump), this often means giving two smaller injections rather than one large one.
With an insulin pump, an extended bolus can be programmed more precisely.
As a general guide:
1 FPU ≈ 0.5 units of insulin
For mixed meals, a dual bolus is often recommended [2]:
FPU coverage is especially useful for large mixed meals (e.g., barbecues).
How Much Basal Insulin Is Needed?
People with type 1 diabetes require insulin throughout the day, even when not eating.
Without basal insulin, the liver continually releases glucose (via glycogenolysis), and blood glucose will rise, potentially leading to hyperglycemic coma.
Basal insulin should maintain normal glucose levels during fasting.
The basal requirement is individual.
In adults, the bolus : basal ratio is roughly 50 : 50, in children around 65 : 35 (less basal).
Types of Basal Insulin
Previously, NPH (Neutral Protamine Hagedorn) insulin was common.
It acts for 6–10 hours, depending on dose, so it must be injected 2–3 times daily and mixed thoroughly before use.
Modern long-acting insulin analogs have largely replaced NPH.
They are molecularly modified for slower absorption:
However, insulin detemir will be withdrawn from the market in 2025.
Newer options include:
Fasting Blood Glucose — “The Diva”
Fasting glucose levels are the hardest to control.
NPH insulin is often too short-acting — it peaks at ~4 hours, then declines.
Meanwhile, morning hormones (catecholamines, cortisol, growth hormone) raise insulin resistance, causing high fasting glucose.
Long-acting analogs manage this better, but cannot always counter the dawn phenomenon — a rise in blood sugar in the early morning due to counter-regulatory hormones.
When this effect is strong, even analogs may fail.
In such cases, an insulin pump is indicated, as it allows hourly adjustment of the basal rate.
[1] The Diabetes Control and Complications Trial Research Group (1993).
The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus.
New England Journal of Medicine, 14: 977–986.
[2] Pankowska E et al. (2008).
Three kinds of mealtime insulin administration and metabolic control in diabetic children on insulin pumps.
Diabetologia, 51 (Suppl. 1): S381.