This is one of the most popular questions about sleep that is asked on Google, which is interesting as I think it’s an under-appreciated aspect of weight loss.

The fact is, sleep plays a major role in fat loss (and in muscle gain as well). Sleep is a critical factor for almost every aspect of our health.

So how can a lack of sleep affect weight loss? There are three major implications to a lack of quality sleep – and they’re all linked to hormones.


Ghrelin is a hormone that regulates our appetite – its nickname is the hunger hormone. Ghrelin tells our brain that we’re hungry, and when it’s working well, we can rely on it to steer us towards food when we need it. It’s like following your intuition – you’ll know what to eat and when to eat. When you’re sleep deprived, there can be too much ghrelin in your system, causing feelings of hunger. This makes you far more likely to overeat and gain weight.


Leptin is a hormone that regulates satiety – leptin tells the brain when we’re full. When we’re sleep deprived, we can end up with too little leptin in our bodies, which makes your brain think you need energy, and creates feelings of hunger. This can cause you to overeat and more likely to crave glucose-rich foods such as refined carbohydrates.

The perfect storm

When you combine these two factors – increased ghrelin and decreased leptin levels – you have a perfect storm for weight gain or hindered weight loss. Add into this that when you’re tired, you lack motivation to exercise or cook healthy foods, it’s clear to see the influence that sleep has on weight loss.


The other hormone that plays a role in tiredness and sleep deprivation is cortisol. Cortisol is the stress hormone, which is an important hormone for functions such as regulating metabolism and contributing to your immune response. Cortisol levels should be highest in the morning and come down as the day progresses and hit their lowest point before bedtime. When you’re sleep-deprived, cortisol levels go up, and this increases blood glucose (sugar) levels. Whilst this isn’t ideal, it’s not a huge issue if it’s intermittent or infrequent, because your pancreas will produce insulin to ‘mop up’ the glucose and transport it to the muscles, liver and fat cells. The problem is sleep deprivation can reduce your insulin sensitivity, which means your blood glucose could be elevated. This is a scenario you want to avoid and can cause unstable energy levels.

Main takeaway

Sleep is essential for good health, and this includes weight management. If you’re looking to lose weight, review your sleep routine first.

Leanne Spencer

This article first appeared in the March 2018 issue of SE22 magazine.