Melatonin (Sleep hormone) reduces insulin secretion and why that is important

Melatonin is a hormone that helps regulate our wake and sleep cycles. It is released at greater and greater amounts the later in the day it gets. What does a sleep hormone have to do with insulin? Let me explain. It’s fascinating. At least to me. 🙂

We have been told for years that it is a bad idea to eat at night. Nobody was ever really sure why but it was just one of those bits of advice that has always floated around. Sometimes these bits of wisdom passed down are exactly right and what we should be listening to. Here is some science to back up this particular gem.

The study below looked at the effect of melatonin on insulin secretion. It was found that melatonin binds to receptors on the insulin producing beta cells in the pancreas and limit the amount of insulin they can secrete. In addition to this, about 30% of the population have a mutation of these receptors that cause an increased sensitivity to melatonin and will secrete even less insulin in response to melatonin.

https://www.cell.com/cell-metabolism/pdfExtended/S1550-4131(16)30160-7

What is the relevance to this and eating at night? Isn’t less insulin a good thing? That depends. It isn’t a good thing to a type 1. It also isn’t a good thing if you are eating food that may raise blood glucose. You need insulin to put away that glucose where it is supposed to be and not left in the blood. Lets look at what happens when you eat at night. We will use a carb meal as an example to start then we will discuss a low carb and protein rich meal.

  1. food is consumed and digested
  2. blood glucose rises
  3. Insulin should come in now and push glucose out of blood and where it should be like the liver and muscles. Since insulin is suppressed by melatonin, the glucose levels in the blood rise.
  4. High blood glucose is a negative situation for the body. It is damaging to blood vessels and needs to be dealt with. To deal with this the body up-regulates utilization in order to get rid of the glucose. When glucose is being preferentially oxidized then fat cannot be used.
  5. Since usually energy expenditure at night is low blood glucose stays elevated.

So if you consume anything that will elevate blood glucose at night when melatonin is elevated you will have high blood glucose throughout the night and you will be preferentially using glucose for fuel due to the bodies need to get rid of the glucose in the blood. This means less fat being used at night.

Now lets look at what happens when you consume protein.

  1. food is consumed and digested
  2. insulin normally comes along to help shunt amino acids into cells where they are needed. Since insulin is suppressed we will not have the amino acids being sent to where it needs to go and we cannot effectively use these building blocks for what they are intended for. The body will use them as fuel at this point as having free floating amino acids is also a negative situation. Since protein does not contain glucose there will not be a rise in glucose directly so that is not an issue so far. But……
  3. In addition to the above, with protein consumption you also have a glucagon response. Glucagon is a counter regulatory hormone to insulin. Where insulin puts energy away for storage, glucagon brings it out for use. The reason we get a glucagon response with protein is because it has an insulin response and an insulin response in a food that contains no carbohydrate would result in low blood glucose and that is a negative as well. To combat that the body is smart and releases glucagon simultaneously to raise glucose levels in the blood to counter the drop from the insulin response.
  4. The glucagon response starts looking for glucose to raise blood sugar. If you are in a glycogen depleted state, like a low carb/ketogenic diet, your body will start making glucose from amino acids. This is a problem because without the insulin to counter act the glucagon response you end up with high blood sugar.
  5. You now have elevated blood glucose, despite not having any carbohydrate, and also a mass of free floating amino acids. These two things are both problematic and will compete for space in fuel utilization.

I hope this throws some light on why it is a bad idea to eat and night and how complex our body is. It is still not completely understood as to why melatonin suppresses insulin but it is hypothesized that it is a protective mechanism to prevent against night time hypoglycaemia (low blood sugar). In the evening it was more typical that food intake was low in most of our evolution so this inhibition of insulin secretion would allow for more fuel available in the blood for longer. What we do know is that having high glucose levels in the evening is not a great idea. Eat early and stop early.

Keto ON,

Coach Jack

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