Exercise is a great way to lose weight, but it’s not the only way to do it. If you can’t, or simply don’t want to, exercise, you can focus on another thing that has arguably more impact on your weight: sleep.
How much sleep you get, and when you get it, can make or break your weight loss journey, as getting it wrong can not only make losing weight harder, it can actually cause you to gain weight. Plus, as much as you need to eat healthy foods and to be in a calorie deficit to lose weight, when you eat can also impact your weight, as well as impact how well you sleep each night.
Below, we’ll dive into how lowering your sleep debt, aligning with your circadian rhythm, and eating at the right times for you can help you lose weight — all without an exercise routine.
It’s not just lack of exercise that leads to weight gain, your sleep, circadian rhythm, and how your diet affects them, all have huge impacts. So, getting these things right can make your weight loss journey much easier.
Sleep deprivation, believe it or not, impacts your body weight massively. Studies show if you sleep for a short amount of time each night you’re more at risk of obesity. And it doesn’t take a lot of lost sleep to increase the risk.
Research suggests sleeping for just one hour less per night is associated with a roughly 0.07 pound per square foot increase in body mass index (BMI). Or, more simply, if you’re 5 foot 8, you’d put on about 3 pounds in weight, just by sleeping one hour less a night.
One reason this happens is because sleep affects the hormones responsible for your appetite. When you don’t get enough sleep, ghrelin, the hormone that makes you feel hungry, rises, but leptin, the hormone that reduces your appetite, falls. This leads to increased hunger levels, and therefore increased calorie intake.
Plus, when we’re tired, our cravings for unhealthy foods go up, so we’re much more likely to reach for high-calorie foods and junk food. Our brain’s prefrontal cortex isn’t working as well as it should, meaning we have much less self control, so we just want to eat comfort food.
Not getting enough sleep also has huge impacts on your glucose metabolism and insulin levels. Research shows short sleepers who get less than 6.5 hours of sleep a night produce about 50% more insulin and have 40% lower insulin sensitivity than those who sleep for 7.5 to 8.5 hours a night. Having excess insulin in your system can lead to increased hunger levels, insulin resistance, type 2 diabetes, and excess glucose in the blood being stored as body fat.
So, by not getting enough sleep, you eat more, usually do less physical activity as you’re tired, and your body’s natural biology works against your weight loss efforts. We’ve covered other reasons why you can’t lose weight here.
Meeting your sleep need — the genetically determined amount of sleep you need each night — can reverse the damage if you’ve not been getting enough sleep. One study found just two nights of getting enough sleep restored normal glucose metabolism. You can find out what your exact sleep need is with a tool like the RISE app. The app uses your phone use behavior over the past year to determine your sleep need, so you know the right amount of sleep you should be aiming for.
It’s not all about how long you sleep for, when you sleep also plays a role in weight loss. Your circadian rhythm is your internal body clock that runs on a roughly 24-hour cycle. Being out of sync with your circadian rhythm can make it harder to get enough sleep each night — and therefore increase the likelihood of being sleep deprived — but it can also lead to weight gain itself.
One study looked at participants who were 12 hours out of sync with their circadian rhythms — this might be you if you’re a night shift worker. The results showed they had a 17% decrease in leptin, a 6% increase in glucose, and a 22% increase in insulin. Even if they got enough sleep, their leptin levels were still affected just by being out of sync, leading to increased hunger.
Research from 2021 looked at two groups of mice eating the same diet. The mice who were out of sync with their body clocks by about three hours had higher blood sugar levels, fattier livers, and gained more weight as their metabolisms were negatively impacted.
“When the external world doesn’t match the internal body’s cycles, metabolism pays the price,” said Mitchell A. Lazar, MD, PhD, the senior author of the study and the director of Penn Medicine’s Institute for Diabetes, Obesity, and Metabolism. “We saw this in our study, and we believe that this happens similarly when people work odd hours that don’t align with how human bodies are wired.”
However, just like with sleep deprivation, it appears the damage is reversible. Once the mice got back in sync with their body blocks, their metabolism started working correctly again.
It’s not just night shift workers who are at risk. Even being just a few hours out of phase with your circadian rhythm can make weight loss harder.
Social jetlag is when your body clock and your social clock are out of phase — for example, maybe you go to bed a few hours later on the weekends, only to have to wake up early again come Monday. If so, you’re not alone. About 87% of adults have social jetlag and go to bed at least two hours later than usual on weekends.
Research suggests having social jetlag is associated with having a higher BMI, though. And it may lead to having a higher weight, even if you get enough sleep. A 2015 study found participants with more social jetlag had higher BMIs, higher inflammation, metabolism dysfunction, more fat mass, and were more likely to be obese, even when sleep deprivation was taken into account.
Even social jetlag of just one to two hours has been shown to increase the prevalence of metabolic syndrome compared to those who have less than an hour of social jetlag.
Of course, even if you are exercising, what you eat is important for weight loss. We know we should keep an eye on our portion sizes and eat a nutrient-rich diet full of veggies, whole grains, and healthy fats. But when you eat may be just as important as what you eat.
There’s research to show that simply eating your breakfast before 8:30 a.m. could help to prevent type 2 diabetes. The study found people who ate breakfast earlier had lower blood sugar levels and less insulin resistance than those who ate it later. And this was true regardless of whether the people were practicing time-restricted eating — whether they ate their meals in a 10-hour window or a 13-hour window (more on this soon).
"Timing is what's important, and earlier seems to be better," said Kristen Knutson, the study author and an associate professor at the Center for Sleep and Circadian Medicine at Northwestern University. "Our ability to process the food we eat works better in the morning."
What time of day you eat your calories may impact your weight, too. One study looked at two groups who ate the same amount of calories each day. The first group ate the bulk of these calories in their breakfast meal, and then less at lunch and dinner. And the second group did the opposite, eating more of their calories at dinner. The results showed those who ate most of their calories at breakfast lost more weight and had a bigger reduction in their waistline circumference. They also experienced lower levels of insulin, glucose, and ghrelin, and higher levels of satiety.
When you eat also impacts your sleep. And, as we’ve already covered, getting enough sleep at the right times for you can massively affect your weight.
Eating too late in the day can make it more difficult to fall asleep and stay asleep all night. Digestive issues may keep you awake and if you have spicy, fatty, or sugary meals, alcohol, or caffeine — like chocolate for dessert — these may disrupt sleep, too. On the plus side, we covered more about what foods can improve sleep here.
Plus, eating your last meal too late in the day and eating meals at different times each day has been shown to throw off your circadian rhythm and negatively impact your metabolism.
A 2021 study found eating at night can lead to impaired glucose intolerance and misalignment between your master body block — located in the suprachiasmatic nucleus (SCN) in the brain — and peripheral circadian clocks — which are found in almost every tissue and organ in the body. Eating during the day only, however, stopped this from happening, even when participants were awake at night.
So, only eating during daytime hours, even if you’re awake at night, may help keep your circadian rhythm in check and reduce some of the negative effects being out of sync has on your weight.
The study looked at the effects on night shift workers, but this is also important for anyone who sleeps in and therefore eats a lot later on the weekends, or those trying to overcome jetlag.
Here are the science-backed ways you can lose weight that don’t involve exercise.
We’ve shown how short sleepers are much more likely to be overweight. But can sleeping for longer at night really help people lose weight without exercise? It can! Research suggests extending your sleeping times can help with weight loss without any other intervention, including exercise and even diet.
A 2022 study looked at overweight participants who slept less than 6.5 hours a night. Researchers helped them improve their sleep hygiene (more on that soon) and extend their sleep by about 1.2 hours a night. The result? Participants ate 270 fewer calories each day, which would equal 26 pounds of weight loss over three years. Some participants even ate 500 fewer calories a day. And all this came from simply sleeping longer.
“Many people are working hard to find ways to decrease their caloric intake to lose weight,” said Esra Tasali, MD, Director of the UChicago Sleep Center at the University of Chicago Medicine and lead researcher on the study. “Well, just by sleeping more, you may be able to reduce it substantially.”
We’ve also shown how a lack of sleep can lead to eating more and storing more body fat. You can catch up on sleep, but first you need to know how much you need to catch up on.
Sleep debt is the measure of how much sleep you owe your body over the last 14 nights. If you’ve been consistently sleeping less than your sleep need, you’ll have built up quite a bit of sleep debt, which may be affecting your weight loss goals.
RISE calculates how much sleep debt you have and keeps track of it as you work to pay it back. In an ideal world, we’d all be meeting our sleep need each night, but we know that’s not always possible. So, we recommend aiming to keep your sleep debt below five hours to feel and perform your best, and make weight loss easier.
If you find you have more than five hours of sleep debt, you can pay it back by:
Research suggests simply being out at odds with your circadian rhythm can lead to weight gain. The RISE app can help you learn more about your circadian rhythm, so you can start aligning your schedule with it, and that’s where sleep hygiene can help.
Sleep hygiene is a set of behaviors you can do throughout the day that will help you sleep come nighttime. This’ll help you meet your sleep need and not disrupt your circadian rhythm by helping you fall asleep at a similar time each night and doing behaviors that regulate the cycle.
Here’s what you can do:
The RISE app can tell you the right time to do these behaviors based on your circadian rhythm each day.
When we eat something, our pancreas starts releasing insulin to absorb sugar from the blood into certain organs. It also tells these organs to convert some of this sugar into body fat. This process continues for two to three hours after eating, and even longer after our last meal. The pancreas releases more insulin during the first half of the day and slows down come nighttime. So, our body is in fat-making mode for most of the day, only switching to fat-burning mode when we haven’t eaten for six to seven hours.
To avoid weight gain and promote weight loss, give your body windows of time to start burning fat. This can include not eating your late meal too close to bedtime, so you fast for longer overnight. You could also consider time-restricted eating — although speak to your doctor before embarking on a serious change in diet.
You may have heard the hype around intermittent fasting or time-restricted eating (TRE). It involves eating all of your meals in a shorter window of time and fasting for the rest of the day and night. For example, you might keep your food intake between 12 p.m. and 8 p.m., and fast outside of this window (an example of a 16:8 diet in intermittent fasting speak; 16 hours of fasting, 8 hours of eating). Some diets even have much shorter windows of eating time, or have one to two days of restricted calorie intake each week.
Experts are divided, but there is some evidence to show time-restricted eating may help with weight loss, and it may also have a lot of other health benefits. One paper looked at many studies and concluded intermittent fasting may reduce the risk of things like cancer, cardiovascular disease, diabetes, and obesity. In animals, intermittent fasting has been shown to prevent obesity caused by a high-fat diet. Six studies have even shown intermittent fasting may be as effective for weight loss as weight-loss diets.
A reason for this is that it’s much harder to overeat if your meals are restricted to a short time window. You’re also much less likely to eat late at night, which as we’ve shown, disrupts your sleep and metabolism.
However, while there is research to show intermittent fasting can help with weight loss, there’s also some evidence that says it may not, particularly if you’re already in a caloric deficit or a woman.
A recent study, published in 2022, looked at people with obesity who followed a calorie-restricted diet for 12 months either eating within an eight-hour window or eating regularly throughout the day. The results showed there was only a very small difference — about 4 pounds — in weight loss between the two groups. While some in the media claimed this proved time restricted eating to be ineffective for weight loss, this study only shows caloric restriction plus TRE might not promote weight loss. More research needs to be done comparing time-restricted eating alone to being in a calorie deficit. Studies also need to look into whether different fasting lengths are better for targeting weight loss or other health benefits.
Even if you decide more intense time-restricted eating isn’t for you, research shows keeping your meals for the day within a 12-hour window is best for overall health and well-being, and it can be a more sustainable practice for many.
When you eat can be just as important for weight loss and what’s actually on your dinner plate. Here are the simple ways you can change your eating habits to help you lose weight or maintain a healthy weight.
Here’s a round up of advice from science we’ve covered in this article:
You don’t need to hit the gym every night or sweat it out on a long run to lose weight. By focusing on your sleep and circadian rhythm, and how your diet affects these things, it is possible to lose weight, all without working out.
Work to lower your sleep debt, align with your circadian rhythm, and eat at the right times for you. The RISE app can help with all three.
The app will calculate how much sleep debt you have and keep track of it as you pay it back. It’ll predict your circadian rhythm each day and show you it on the Energy screen, so you can sync your schedule up. Plus, it can remind you when to do things like eat your last meal based on your body clock.
You can lose weight without exercising by focusing on your diet, sleep, and circadian rhythm. Aim to meet your sleep need each night and keep sleep and eating times in alignment with your circadian rhythm.
The fastest way to lose fat without exercising is by focusing on the timing of your meals and your sleep. Eating meals earlier in the day and in a restricted time window, plus getting the right amount of sleep at the right times for you can help you lose weight.
To burn fat naturally without exercise, focus on diet and sleep. Getting enough sleep each night and staying in sync with your circadian rhythm, plus eating a healthy diet at the right times of day for you can help you burn fat.
RISE makes it easy to improve your sleep and daily energy to reach your potential
RISE makes it easy to improve your sleep and daily energy to reach your potential