You've spent a week reading your CGM differently. Today, you learn the single most-cited technique in the Pro Tip series — and why most people never get it right the first time.
Today's idea
A pre-bolus is the practice of giving insulin some time to start working before food enters your system. It's not just "bolus before you eat." It's "time the insulin so it's active as the carbs become active."
That distinction is everything. Rapid-acting insulin needs about 15–30 minutes to come online. If insulin and carbs enter your system at the same moment, the carbs have a head start the insulin can never recover. The math you did at the meal was correct. The timing wasn't.
The Pro Tip series puts it this way:
Rapid-acting insulin isn't actually rapid. It takes 15 to 30 minutes to come online. Yet most patients are still told to take it and start eating. That timing mismatch produces post-meal spikes — every time.
From Pro Tip 1003
The exact pre-bolus timing depends on you. Your insulin. Your site. The food. Whether you started high or low. The episode walks through how to find your own number. Today, the point is just that the number exists — and that taking insulin and eating at the same moment almost guarantees a post-meal spike.
Timing matters as much as amount.
Today, notice the gap between when you take your insulin and when food enters your mouth. Don't change anything. Just notice what the gap currently is, and what your CGM does in the 90 minutes after.
Small Sip #1421 — Insulin Used Now Is For Later
What did I notice about the rhythm of insulin and food today?