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Happy Friday everyone – the last day of March!

For those who feel it is appropriate to reintroduce alcohol to their weekend, the one glass Friday/Saturday is “allowed”.  With a last look at sleep, I am tying this post with sleep/will-power which also has a connection with alcohol/fatty, sweeter food cravings.

There is a wealth of data that shows how sleep deprivation alters biological processes in our bodies, how our brain functions and how we behave in our day to day lives. Looking at the the various components, then, we see that a reduction in sleep causes the following changes:


  • Willpower is reduced ↓
  • Pleasure and rewards centre signalling is enhanced ↑


  • Low leptin makes feelings of fullness decrease ↓
  • High ghrelin makes feelings of hunger increases ↑


  • Less inclined to exercise ↓
  • More inclined to sit and do nothing ↑

While it makes it easier to see the different effects by grouping into these three separate categories, in reality all three interact. The body sends chemical signals to our brain. Our brain processes these messages and we react in certain ways.

Many of our hormones are affected by lack of sleep, with several identified as being directly involved in why we gain weight when we don’t sleep well.

Two such hormones are known to be important for regulating our drive to eat. These are ghrelin and leptin. They have roughly opposite effects: ghrelin makes us feel hungry and leptin is mostly responsible for making us feel full. In this way, ghrelin is our signal to go and eat and leptin tells us when to stop.


Leptin is mainly produced by fat cells in the body and it works to regulate our fat levels by controlling appetite. The amount of leptin released is directly related to the amount of fat in the body. More fat equals more leptin.

In a healthy person carrying excess fat, leptin levels increase and this signals the brain to reduce appetite accordingly. The body can then use some of the fat stores to power itself, thus lowering the levels of stored fat.

↑fat cells → ↑levels of leptin→ ↑signals to the brain → appetite ↓

When we get enough sleep, leptin levels should increase steadily during the night, peaking around 2am. This gradual rise during the night may have evolved so that we don’t feel hunger when we should be sleeping.

Many studies have looked at how leptin levels are affected by sleep duration and the consensus seems to be that leptin levels decrease in sleep-deprived individuals.

When we fail to get enough sleep our leptin levels remain low. The brain believes that the body needs to take in more energy.

The brain then sends hunger signals and we end up eating, even though we don’t actually need the energy! The calories taken in are stored as fat because the body thinks that it needs to build up reserves. 


Ghrelin is mostly made in the stomach and is known as the ‘hunger hormone’ because it’s responsible for making us feel hungry.

Just before we eat, ghrelin levels in the blood increase and this is thought to give rise to the hunger pangs which prompt us to eat. Once we’ve eaten, our ghrelin levels decrease.

What we eat affects ghrelin levels: carbs and proteins lead to a greater decrease in ghrelin than fats, so healthier options may leave you feeling fuller than, for example, a fast-food burger.

When we sleep, our ghrelin levels naturally decrease because our bodies don’t need to burn as many calories when we’re not active. But when we don’t get enough sleep our ghrelin levels don’t decrease as much as they should. Feelings of hunger persist even when the body doesn’t need more calories.  Alcohol will disrupt sleep encouraging those hunger pangs.

So by altering these two key hormones, sleep deprivation leaves us feeling both hungrier and also less full that we actually are. It’s not hard to see how this situation can – and will – lead to an increase in body size.

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