What is insulin?
Insulin is a hormone, a chemical messenger made by the pancreas, that tells your cells to take sugar out of the blood and store energy.
Think of insulin as a key. After a meal, sugar waits outside your cells like delivery trucks at a locked warehouse. Insulin unlocks the doors so the sugar can be unloaded and stored.
Why it matters for aging
Sugar from food raises insulin the most, protein raises it moderately and fat raises it very little. That's why sugar and protein "break" a fast and black coffee doesn't.
Besides moving sugar into cells, insulin is a growth signal: it helps switch on mTOR, the cell's "build and grow" switch, and switches off fat burning. Constantly high insulin keeps the body in storage mode, which is part of why insulin resistance is linked to weight gain and faster aging.
A common myth
Insulin is the enemy, and you should keep it as low as possible.
Insulin is essential; without it, you can't use the food you eat. The problem is when cells stop responding well and the body has to make more and more of it. That's insulin resistance.
Go deeper
Deep dives
- Early signs of insulin resistance, and what comes before them
- Does coffee break a fast? It depends what you're fasting for
- Berberine vs metformin: what the evidence actually says
Related terms
Updated Nov 9, 2026 · All terms