Fat Loss Factors Post 1: Sleep

5 mins read
Written by:
The BodySpec Team

Yes, yes, we all know you’re supposed to get 8 hours of sleep each night. But that new Netflix series keeps sucking you into more episodes! So how much does it really impact your health if you aren't getting enough quality sleep? Let’s explore sleep, hormones, and the impact it may be having on your ability to lose fat.

What happens when we sleep?

When you sleep, your body has a chance to repair and reboot, so to speak. Especially if you are working out a lot, or under stress in your day to day life, this is the primary opportunity for your body to heal itself. Studies show that young, otherwise healthy individuals who are chronically sleep deprived exhibit signs associated with being much older - impaired blood sugar regulation, impairments in metabolic hormones such as thyroid, and impaired memory.

Impact on cortisol and stress

With adequate sleep, cortisol (a stress hormone) declines to a level that is healthy. Without adequate sleep, the opposite happens: cortisol remains elevated, putting your body into a state of chronic stress and setting off a cascade of other consequences. One study showed that after a single night of only 4 hours of sleep, cortisol levels the following evening were 40% higher than the previous evening. Cortisol levels should be rapidly declining in the hours before bed, to allow your body to slow down and enter sleep easily.

But how do elevated cortisol levels result in alterations to metabolism and weight gain?

Cortisol is linked to insulin resistance. When your body becomes resistant to insulin, it cannot burn up the sugar in your blood effectively and as a result that sugar becomes stored as fat, primarily stomach fat. Insulin resistance is a precursor to diabetes, and the farther you go down that path, the harder it is to reverse. We will explore cortisol and fat loss further in a follow up post on stress.

Impact on leptin, ghrelin and appetite control

Besides cortisol, other hormones that are affected by sleep include appetite-regulating hormones like leptin. Leptin is released by fat cells and tells your brain that you are satisfied. Ghrelin is released by the stomach and stimulates appetite - it tells your brain to FIND FOOD NOW.

Research shows that after 4 nights of less than 6 hours of sleep, ghrelin levels became significantly elevated. Under stressed conditions, the body begins to shift into protection mode, which means storing calories. The first step is for your body to pump out ghrelin to signal your brain to eat more - and then those additional calories will rapidly be stored as fat. Your willpower will only take you so far in this scenario - we’ve all been there! When we are exhausted, it is so easy to munch away mindlessly.

Impact on the thyroid

Maybe you have heard about sleep deprivation affecting cortisol or appetite hormones, but did you know it directly impacts the thyroid too? After multiple days of partial sleep deprivation, studies show a significant increase (not good!) in levels of thyroid stimulating hormone (TSH). A properly functioning thyroid is critical to a range of cellular functions throughout the body, notably metabolism. If sleep deprivation is directly impacting thyroid function, that can have an immediate impact on body weight by slowing down the rate at which you are burning calories.

Takeaway message: Get enough sleep!

The simple message here is to do everything you can to get enough sleep on a consistent basis. Think of it as the best diet advice you can get!

But how much is enough? It depends on your age. Here’s a handy chart to help you determine how much is ideal for you:

Age GroupRecommended Amount of Sleep
Newborns15 - 17 hours
12 months10 hours at night and 4 hours of naps
2 years11 - 12 hours at night and 1-2 hours of naps
3 - 5 years10 - 13 hours
6 - 13 years9 - 11 hours
14 - 17 years8 - 10 hours
Adults7 - 9 hours

Source: Mayo Clinic Sleep Chart

It does seem like 8 hours of sleep is the optimum amount for most adults. Everyone is certainly different, but most research concludes that less than 6 hours of sleep is associated with the issues mentioned above. Interestingly, getting more than 9 hours of sleep also seems to show some negative effects.

It's worth noting that you CAN reverse the short term effects of a few nights of shortened sleep by catching up with a couple full nights of quality sleep. But ideally, you want to aim to get in your 8 hours as consistently as possible, so you aren't cycling in and out of those stressful states.

Stay tuned for a follow-up post with some different apps, trackers, and tips for helping you to dial in your sleep habits!




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