Skip to content
Updated

What does the pancreas do after a meal or during a fast?

Give a juice or a meal, then let time pass without eating. Watch sugar enter the cells, and the hormones take turns.

No food for 3 h
Time speed

Simplified simulation of a healthy person, to understand the main steps. Real values vary from person to person. This is not a medical tool.

Shown in humans

Sugar (glucose)Energy from the meal, carried by the blood.
Insulin, the entry keyReleased by the beta cells. Its key has a round head. It opens the lavender doors: sugar enters the muscles, fat and liver.
Glucagon, the exit keyReleased by the alpha cells. Its key has a square head. It opens the liver's green door: stored sugar goes back into the blood.
KetonesMade by the liver from fatty acids when the fast goes on. The brain and muscles use them as fuel, no key needed.
Fatty acidsReleased by fat cells when insulin is low. The muscles and liver burn them, the brain does not.
Fat cellsThey grow a little after meals and shrink slowly while fasting: about 1% of the reserve per day. Their size is exaggerated so you can see it change.
Golden grains (liver and muscles)Glycogen: stored sugar. The liver's serves the whole body, the muscles' stays in the muscles.
Doors and locksEach key turns in its lock and the door opens for a moment, in the direction of the arrow. During hard effort, muscle opens its doors without a key.

Frequently asked questions about the pancreas, meals and fasting

How long after a meal does blood sugar return to normal?

Usually 2 to 3 hours after the meal. Blood sugar most often peaks within the hour after the start of the meal, then insulin brings it back down. In a person without diabetes, it stays below 140 mg/dL (7.8 mmol/L) 2 hours after the meal (International Diabetes Federation, 2011).

What does the pancreas do when you don't eat?

It lowers insulin and raises glucagon. Glucagon pushes the liver to release its stored sugar, then to make ketone bodies from fat. Insulin never drops to zero: a small baseline level stays so that fat does not melt away too fast (Cahill, 2006).

Does fasting give the pancreas a rest?

Partly: during a fast, the cells that make insulin work much less. In diabetic mice, 4-day cycles of a diet that mimics fasting even made these cells grow back (Cheng, 2017). In humans, this has not been shown.

Does the pancreas also help digest food?

Yes: besides insulin, it makes pancreatic juice, rich in enzymes that break down sugars, fats and proteins in the gut. This juice is released mostly during and just after meals.

Sources

  1. Cahill, "Fuel metabolism in starvation", Annual Review of Nutrition, 2006. pubmed.ncbi.nlm.nih.gov
  2. Cheng et al., "Fasting-Mimicking Diet Promotes Ngn3-Driven β-Cell Regeneration to Reverse Diabetes", Cell, 2017. pubmed.ncbi.nlm.nih.gov
  3. International Diabetes Federation, "Guideline for management of postmeal glucose in diabetes", 2011. www.idf.org