When it comes to losing weight, many people want to lose belly fat. But that’s easier said than done. Fat held around the stomach is often the hardest to lose and it’s the most damaging to your health, too. And while there are plenty of fat loss tips out there, there are two science-backed methods that are often overlooked — and both of them are to do with your sleep.
In this blog post, we’ll explain how sleep debt and circadian alignment can make or break your weight loss efforts. Get them wrong and you’ll find losing belly fat much harder to do and can even gain weight. Get them right, however, and you’ll boost your weight loss efforts as well as your overall health, productivity, and energy levels.
Belly fat is body fat that’s stored around the stomach area, but there are actually two distinct types of belly fat.
Belly fat can be caused by anything that causes you to gain overall body fat like:
Let’s dive into those last two in detail.
You may think weight loss is all about a healthy lifestyle focused on diet and exercise, but sleep plays a foundational role. Firstly, not getting enough sleep leads to people eating more calories the next day. You burn fewer calories when you’re tired as you’re less likely to do physical activity, and you also begin craving processed foods, high-calorie foods, and foods with a high carbohydrate content. Sleep deprivation also leads to insulin resistance, which can cause the body to store more body fat.
But it’s not just weight in general you gain when you don’t sleep enough, it’s belly fat. A 2022 study found getting four hours of sleep a night caused participants to eat more calories, gain weight, and gain abdominal fat, both subcutaneous and visceral. Even more surprising? It didn’t take long for a lack of sleep to cause these things. The participants had restricted sleep for 14 nights, something many of us experience in day-to-day life.
Research shows those who regularly sleep for less than six hours a night tend to have a higher body mass index (BMI), fat percentage, and abdominal circumference than those who sleep for seven to eight hours a night. Another study found those who slept for five hours or less a night were more likely to have a larger waist circumference and be obese than those who slept seven to nine hours a night.
And it’s not just how long you spend in bed at night. Research suggests low sleep efficiency — the measure of how long you spend in bed actually sleeping — is associated with obesity in general as well as abdominal obesity, which is having a waist circumference of more than about 35 inches for men and more than about 33 inches for women.
There is no magic number of hours everyone should sleep for each night, however. Instead, it’s all about meeting your sleep need, or the genetically determined amount of sleep you need each night. And this is different for everyone. In fact, the average sleep need is 8 hours 10 minutes, plus or minus 44 minutes or so, but 13.5% may need 9 hours or more sleep a night.
A tool like the RISE app can take the guesswork out of finding out your sleep need and give you a number to aim for each night in hours and minutes.
Even if you’re getting enough sleep, if you’re not getting it at the right times for you, you may still gain belly fat. This is where your circadian rhythm comes in. Your circadian rhythm is your body’s internal clock. It runs on a roughly 24-hour cycle and dictates when you feel awake and sleepy, as well as changes in your body temperature and hormone production.
A 2019 study found those who disrupted their circadian rhythms — such as through shift work or irregular sleep and meal times — had a higher risk of both general obesity and abdominal obesity.
You don’t need to do much to disturb your circadian rhythm, though. Social jetlag is when your social clock is at odds with your body clock. For example, perhaps you stay up an hour or two later on the weekends than you do during the working week. Research shows people with more social jetlag have higher BMIs, more fat mass, and a more likely to be obese, even when taking into account for how long they slept for.
Even one extra hour of social jetlag can make a difference. One study found those with one to two hours of social jetlag had 1.29 times the prevalence of metabolic syndrome — which includes obesity, diabetes, and high blood pressure — than those with less than one hour of social jetlag. If you have two hours or more of social jetlag? The prevalence rate is 2.13 compared to less than one hour of social jetlag.
If your circadian rhythm is out of whack, the hormones responsible for your hunger and appetite will be too. Sleeping about 12 hours out of sync — which you might do if you work night shifts — has been shown to decrease leptin (the hormone responsible for suppressing appetite) by 17%, and increase glucose by 6%, and insulin by 22%. It also reduced sleep efficiency by 20%.
Being out of sync with your circadian rhythm can also make it harder to meet your sleep need each night, which as we explained above, can lead to an increase in belly fat and make losing weight even harder to do.
Unfortunately, there’s no way to “spot reduce” fat loss. You can’t just do crunches, for example, to choose where exactly you’ll lose fat. And there’s no quick fix, so skip the supplements that promise instant results. Instead, focus on losing fat in a healthy way, and you’ll lose belly fat as part of this.
Eating a healthy diet, exercising, and reducing stress will help you lose belly fat, but as we’ve shown, you need to think about your sleep, too. Here’s what to do:
Getting more sleep may just be the key to keeping belly fat at bay. Research suggests going from sleeping six hours or less a night to sleeping seven or eight hours a night would result in 1 square inch less of visceral fat gain.
Meeting your sleep need each night is the best way to do this, but work and personal commitments (and sometimes just the latest show on Netflix) often stop this from happening. That’s where keeping an eye on your sleep debt comes in handy.
Sleep debt is the measure of how much sleep you owe your body over the last 14 nights. If your sleep need is 8 hours 15 minutes, but you’ve been getting seven hours of sleep a night, you’ll have built up a lot of sleep debt.
Luckily, you can catch up on sleep and pay down some of this debt. We recommend keeping sleep debt below five hours to help you feel and function your best, and to help your weight loss efforts. RISE calculates how much sleep debt you have and keeps track of it as you work to pay it back.
You pay back sleep debt by:
Staying in sync with your body clock keeps everything from your hunger hormones to your sleep schedule in check. Follow these tips to make it happen:
To help you feel sleepy at your desired bedtime each night, you can turn to sleep hygiene. Maintaining good sleep hygiene will also help you fall asleep quicker and reduce how much you wake up during the night, meaning you can stay in alignment with your circadian rhythm and keep your sleep debt low.
Here are some key behaviors to follow:
You can learn more about sleep hygiene behaviors here. To help you stay on top of them all, RISE can remind you when to do 20+ sleep-boosting habits at the exact right time for you based on your circadian rhythm.
While you can’t literally lose belly fat overnight, what you do each night makes a real difference to your waistline. By keeping your sleep debt low and syncing up with your circadian rhythm, you can make sure you don’t make fat loss any harder than it already is. Plus, you can keep additional weight gain at bay.
The RISE app can help. The app works out your individual sleep need and calculates how much sleep debt you have, so you know whether you’re getting enough sleep for you each night. It predicts your circadian rhythm and reminds you when to do 20+ sleep hygiene habits to help you get the sleep you need each night to boost your weight loss efforts each day.
Losing belly fat in a week is hard, but by focusing on sleep, you can make weight loss easier. Lower your sleep debt and sync up with your circadian rhythm to help shift the pounds and keep them off.
Foods that help lose belly fat include fruits; vegetables; high-protein foods like eggs, fatty fish, and nuts; and high-fiber foods like legumes and whole grains.
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