Insulin Dosing: Actual Body Weight vs. Ideal Body Weight
For insulin therapy, dosing should be based on actual body weight for both type 1 and type 2 diabetes, with specific weight-based calculations that account for the patient's total body weight.
Standard Weight-Based Dosing Recommendations
Type 1 Diabetes
- Total daily insulin requirements typically range from 0.4 to 1.0 units/kg/day based on actual body weight, with approximately 50% administered as basal insulin and 50% as prandial insulin 1.
- For metabolically stable patients with type 1 diabetes, a typical starting dose is 0.5 units/kg/day of actual body weight 1, 2.
- Higher doses are required during puberty, pregnancy, and medical illness, potentially exceeding 1.0 units/kg/day of actual body weight 2.
Type 2 Diabetes
- For insulin-naive patients with type 2 diabetes, the recommended starting dose is 0.1-0.2 units/kg/day of actual body weight for basal insulin 1, 2.
- For patients with severe hyperglycemia (A1C ≥9% or blood glucose ≥300-350 mg/dL), consider higher starting doses of 0.3-0.5 units/kg/day of actual body weight 1, 2.
Evidence Supporting Actual Body Weight
The guidelines consistently reference actual body weight (total body weight) rather than ideal body weight for insulin dosing calculations. The American Diabetes Association explicitly recommends weight-based dosing using actual body weight in units/kg/day 1, 2.
Research evidence supports this approach, showing that:
- Volume of distribution for insulin is best described by total body weight, particularly for lipophilic drugs 3.
- In hospitalized patients, weight-based insulin glargine titration using actual body weight (0.2 U/kg initial dose, titrated by 0.1 U/kg increments) was effective and safe 4.
Special Considerations for Obesity
While actual body weight is used for dosing calculations, obese patients demonstrate greater insulin resistance and may require higher doses per kilogram than non-obese patients 5, 6.
- Baseline body mass index is the most significant predictor of glycemic response to insulin therapy, with obese patients (BMI >28 kg/m²) showing less improvement in glycemic control compared to non-obese patients despite similar weight-based dosing 6.
- Insulin resistance in obesity can be overcome at supraphysiological insulin concentrations, but endogenous hyperinsulinemia fails to fully compensate for the resistance 5.
Critical Dosing Thresholds
When basal insulin exceeds 0.5 units/kg/day of actual body weight and approaches 1.0 units/kg/day, consider adding prandial insulin rather than continuing to escalate basal insulin alone 1, 2. This threshold helps prevent "overbasalization," characterized by:
- Basal dose >0.5 units/kg/day 1
- High bedtime-to-morning glucose differential (≥50 mg/dL) 1
- Hypoglycemia and high glucose variability 1
Hospitalized Patients
For hospitalized patients who are insulin-naive or on low-dose insulin, the recommended total daily dose is 0.3-0.5 units/kg of actual body weight, with half administered as basal insulin 1, 2.
For patients on high-dose home insulin (≥0.6 units/kg/day of actual body weight), reduce the total daily dose by 20% upon hospitalization to prevent hypoglycemia 2.
Common Pitfalls to Avoid
- Do not use ideal body weight for insulin dosing calculations - all major guidelines reference actual body weight 1, 2.
- Do not assume obese patients require proportionally less insulin per kilogram - they often require higher doses due to insulin resistance 5, 6.
- Do not continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia - this leads to overbasalization and increased hypoglycemia risk 1, 2.