Your insulin peaked at 90 minutes. Your glucose is rising at hour 3. The carbs were not the problem. Fat and protein slow digestion and cause a secondary rise that catches most MDI users completely off guard.
When you eat a meal containing significant fat and protein alongside carbohydrates, the fat slows gastric emptying. Your stomach holds onto the meal longer, releasing glucose into the bloodstream more slowly and for longer than a low-fat meal would.
Protein has a different mechanism. Roughly 40 to 60% of dietary protein is eventually converted to glucose through a process called gluconeogenesis. This conversion happens slowly, typically over 3 to 6 hours after eating. The result is a secondary glucose rise that begins well after your rapid-acting insulin has peaked and is starting to clear.
The combination of these two effects means a high-fat, high-protein meal can cause your glucose to be rising at hour 3 or 4 even though your pre-meal bolus was perfectly calculated for the carb content.
Not every meal requires a split dose strategy. The clinical thresholds most commonly used are more than 20 grams of protein or more than 15 to 20 grams of fat in a single meal. Below these levels, the effect on glucose is usually manageable with a standard carb bolus.
Above them, carb counting alone is not sufficient. Your CGM will show you a flat or slightly rising glucose in the first two hours, followed by a climb that continues long after you think the meal is covered.
Pizza. High carbs, high fat, high protein. A standard pre-meal bolus covers the early carb spike reasonably well. Then at hour 3 or 4, the fat and protein drive glucose significantly higher. This is not a pump or calculator failure. It is physiology that standard carb-only dosing does not account for.
Not everyone responds to fat and protein the same way. Some people see a 50 to 80 mg/dL rise at hour 3 from a high-fat meal. Others see very little. Your CGM makes this easy to identify.
Run a simple experiment. Eat a meal you normally eat, note the fat and protein content, and check your CGM at 1 hour, 2 hours, 3 hours, and 4 hours after eating. If you consistently see a rise between hours 2 and 4 that you cannot explain with the carb content, fat and protein are the driver.
On a pump, the standard approach is an extended or dual-wave bolus that delivers insulin over 2 to 3 hours to cover the delayed absorption. MDI users do not have that option. The workaround is a split injection.
Step 1: Calculate and give your normal carb bolus before the meal as usual.
Step 2: Calculate the additional insulin needed for fat and protein using the Warsaw method (see below). Give this as a second injection 60 to 90 minutes after the meal.
The timing of the second injection is based on your CGM. If your glucose is flat or slightly rising at 60 minutes, give the second dose. If it is already dropping, hold off and monitor. If it is rising fast, give it sooner.
The Warsaw method converts fat and protein calories into a carbohydrate equivalent and then doses using your standard ICR.
Fat contains 9 calories per gram. Protein contains 4 calories per gram. Add the total calories from fat and protein, divide by 100 to get fat-protein units (FPU), then multiply by 10 to get the carb equivalent grams. Dose that using your ICR.
Your meal contains 30 grams of protein and 20 grams of fat. Protein calories: 30 times 4 equals 120. Fat calories: 20 times 9 equals 180. Total: 300 calories. FPU: 300 divided by 100 equals 3. Carb equivalent: 3 times 10 equals 30 grams. If your ICR is 1:10, your second dose is 3 units, given 60 to 90 minutes after the meal.
The most reliable guide is your own CGM data. After testing this approach on a few meals, patterns will emerge. The delayed rise will be predictable for specific meals you eat regularly. Once you know your pizza needs a 3-unit second injection at the 90-minute mark, that becomes your protocol for pizza.
Keep notes. Meal name, total protein and fat, timing of second dose, glucose outcome at 3 and 4 hours. After 5 to 10 meals you will have personalised data that no formula can replicate.
The main risk of the split dose approach is giving the second dose when your glucose is already falling, which can cause a late low. Always check your CGM before giving the second injection. If you are below 120 and falling, hold off. If you are above 140 and flat, give it. If you are unsure, give half and monitor.
Start conservative. The cost of slightly elevated glucose at hour 4 is lower than the cost of a hypoglycemic episode at hour 3.
The Diabetic Wolf bolus calculator applies everything in this guide automatically. ICR by time of day, CGM trend adjustment, IOB correction, fat and protein split dosing, and exercise modifier.
Open the Bolus Calculator CGM Decision Tool