Sleep plays a key role in both body composition and performance. And slightly pun intended, but its importance is often slept on, despite it being a free and available aid.
In this article, I’ll cover how sleep affects hunger and performance, and how training and nutrition, in turn, affect sleep. If you’re trying to optimize this part of your life, take a moment for this one. You might pick up a helpful tip or two.
Let’s tuck in.
A little background on sleep
Sleep is a series of behaviors and patterns that lead to changes in our brain activity and physiological responses (e.g., breathing, body temperature, and heart rate). The positive side effects of sleep lead to improved neurological health, muscle recovery, and immune health (just to name a few).
| Stages of sleep and what occurs in each | |
|---|---|
| Stage | Definitions |
| Stage 1 (NREM) | Light sleep, easy drifting in and out happen |
| Stage 2 (NREM) | Brain activity starts to slow; sleep spindles and K-complexes appear |
| Stage 3 (NREM) | Deeper sleep, when most of the body’s repair and recovery occurs |
| Stage 4 (REM) | Muscle relaxation and vivid dreams with higher brain activity occur |
| Wake | Pre- or post-sleep occurs with periods of wakefulness, which may or may not present for conscious awareness |
| Abbreviations: NREM, non-REM; REM, rapid eye movement. Inspired by Ramar et al (2021) | |
Most of this article focuses on how sleep affects performance and body composition, and how those goals can also influence your sleep in return. You’ll see a few terms come up along the way that aren’t always part of everyday conversation, so I’ve defined the ones that might trip you up (because many of them are similar but ultimately different).
| A few terms relevant for this article and understanding sleep conversations | |
|---|---|
| Terms | Definitions |
| Circadian rhythm | An internal biological “clock” that regulates shifts in sleepiness or wakefulness largely driven by the suprachiasmatic nucleus (SCN) that is affected by all types of environmental and behavioral stimuli. |
| Sleep architecture | The structure and order of our sleep stages across our sleeping time. |
| Sleep debt | Represents a cumulative sleep loss over time. The term is slightly misleading since “repaying” or “regaining” lost sleep can be difficult. |
| Sleep duration | The total collective amount of time you spent asleep (not just the amount of time you spent in bed). |
| Sleep efficiency | Total sleep time divided by time spent in bed. Can show that too much time is spent trying to sleep versus sleep actually taking place. |
| Sleep extension | Deliberately trying to increase total sleep time, usually by attempting to fall asleep earlier in the night, but not the same as sleep “catch-up.” |
| Sleep fragmentation | How disrupted or how many instances of “broken up” cycles you have during sleep. |
| Sleep hygiene | Habits and environmental cues that can support or harm your sleep behavior. |
| Sleep onset latency | How long it takes you to fall asleep when you’re actively trying. |
| Sleep quality | A general catch-all for how restorative or restful your sleep is. This can include how easily you fall asleep, how often you wake up, and how tired or alert you feel in the morning. |
| Sleep regularity | How consistent your sleep and wake times are from day to day; irregular timing can disrupt your internal clock and lower sleep quality. |
| Inspired by Ramar et al (2021) and Baranwal et al (2023) | |
Caveat: This article doesn’t go into great detail on general health issues. That said, I do think it’s all pretty intertwined, and improvements in sleep tend to spill over into other areas, too. Better sleep usually means feeling and functioning better across the board.
Ideal sleep duration and quality
Generally speaking, most people looking into sleep duration want to know the “ideal” amount that offers the most benefit with the least downsides. However, the research on this topic relies heavily on observational data, which can muddy the waters a bit. For instance, some studies link longer sleep with worse health outcomes, but that might be because people with poor health could sleep more, not because extra sleep causes harm. The same goes for things like phone use before bed. It’s easy to assume that nighttime smartphone use causes poor sleep, but it might be that people already struggling with sleep or stress are more likely to reach for their phones late at night. All these things can bring nuance to the table, and are always something to keep in mind.
With all that said, you’re usually going to find recommendations in a range of 7–8 hours per night associated with better health outcomes (here and here). However, there’s some flexibility. For most people, something in the 6- to 9-hour range is likely fine, as long as it’s consistent and not chronically neglected. Additionally, what can be just as important as duration is regularity (how consistent your sleep is from day to day).
When it comes to sleep, most people have a pretty good sense of whether theirs is working. If you feel rested after 6.5 hours, you’re probably right to trust that. And if you need closer to 9 to feel human, that’s valid, too. I’m not a huge fan of rigid sleep trackers or hard rules like “you must get 8 hours.” In fact, subjective feelings (like tiredness, alertness, or feeling restored) are often ways people evaluate their sleep. So, don’t get caught up in a perfect number, just focus on how you feel and your goals.
How sleep can affect weight management and body composition
Weight regulation tends to get harder when sleep duration drops below what works for you. In general, there’s a strong association between insufficient sleep and poor weight management. If we look at shorter sleep durations, we see small but consistent changes in appetite-regulating hormones like leptin and ghrelin, and these hormonal shifts can become more pronounced as sleep loss intensifies. These effects can also be more pronounced in people with obesity, and can all culminate in a cycle of less sleep, more hunger, and ultimately harder weight management.
Additionally, if you’re not sleeping as much you’re likely spending more time feeling hungry while also having more eating opportunities. And if that extra food intake isn’t offset by increasing your energy expenditure, it can lead to gradual weight gain. To be clear, this doesn’t mean low sleep quality forces you to eat, but it can make food harder to resist. Sleep loss can also reduce your capacity for self-control, making it easier to give in to impulses and harder to stick to goals.
Lean mass retention is another angle when it comes to sleep and body composition. A classic crossover study by Nedeltcheva et al had participants trying to lose weight for 14 days, spending 5.5 hours in bed versus 8.5 hours in bed. Each participant went through both arms of the study, with a 3-month washout period between conditions. All meals were controlled, and their sleep took place in a lab setting.
While total weight loss was similar between the two conditions, the composition of that weight loss wasn’t. In the 8.5-hour sleep condition, participants lost about half fat mass and half lean mass. In the 5.5-hour condition, only about 20% of the lost weight was fat, with the rest coming from lean tissue. In other words, less sleep meant preserving less lean mass.
Longer-term data backs this up as well. A study from Song et al followed 19,770 adults and found that even when total sleep duration stayed the same, a decline in sleep quality showed more muscle loss and fat gain. This helps highlight that while sleep duration matters, sleep quality can play its own role in body composition over time.
To add one more layer, when we look at trying to maintain our weight, the sentiment seems to be the same. One study followed adults with obesity after losing some initial weight (everyone pretty much lost the same amount of weight) and followed them for a 1-year maintenance period. Those who averaged less than 6 hours of sleep per night regained almost 5 kilograms over the year. Those who slept 6 hours or more? They mostly kept the weight off. This suggests that sleep could influence the sustainability of weight loss.
Take home? Whether you’re trying to lose weight or maintain it, your sleep plays a bigger role than you might give credit.
How sleep affects performance
Shifting to performance, inadequate sleep also creates a hormonal environment that’s less favorable for recovery, muscle repair, or training outcomes. For instance, building up a “sleep debt” (consistently getting less sleep than your body needs) can increase your chance of poor muscle recovery. And in general, this ongoing state can reduce testosterone, IGF-1, and growth hormone levels, while also increasing cortisol (chronic cortisol increase is not something we really want). All of this can shift us toward a catabolic state that hinders ideal muscle repair, which is especially unideal for athletes.
Now, poor sleep will affect different types of training in different ways. A systematic review and meta-analysis from Craven et al examined acute sleep loss and its impact on physical performance. In this instance, sleep loss was defined as 6 hours or less (with the baseline being greater than 6 hours). Overall performance drops for all types of training was -7.56%, with the most affected performance being skill (-20.9%) and the least affected being strength (-2.85%).
| Selected examples of performance declines from sleep loss | ||
|---|---|---|
| Training type | Performance change | Notes |
| Skill | -20.90% | Fine motor skills (e.g., serving, shooting) take the biggest hit. |
| Strength-endurance | -9.90% | There is more variability in the studies here, and therefore a wider range of outcomes. |
| Anaerobic power | -6.30% | This can affect things like sprinting and jumping. |
| Endurance | -5.60% | This includes longer duration events and training. |
| Strength | -2.90% | Singles and one-repetition maximum will be more resilient. |
| Speed/power endurance | -2.90% | Moderate decline for short-duration, high-effort bursts in the 30–90 second range. |
| From Craven et al (2022) | ||
Looking at this practically, you’re likely to see that your top-end strength holds up okay, but the average amount of reps or sets feels harder than they probably should. Additionally, anything involving more precise skills could suffer the most (e.g., you might have a harder time putting a basketball in a hoop).
The Craven study also discusses that as the day goes on, performance can decrease, and we are more affected by sleep loss. And that intuitively makes a lot of sense as we are running through resources as each hour passes from waking after less-than-ideal sleep. If it’s one instance here or there, it’s not likely to be an issue you can’t solve with a little caffeine or a nap. But if it’s ongoing, you’ll likely benefit from addressing your sleep schedule.
One final thing to address: even with poor sleep, you still get benefits from training. Ideally, you’d have the best of both worlds (consistent sleep quality and consistent training), but it’s still worthwhile to train during periods when your sleep is less than ideal. For example, while sleep loss can reduce muscle protein synthesis, exercise helps restore it. We also see better glucose control, and even with 1–2 hours of sleep reduction, we can protect our gains in strength and muscle.
The worst-case scenario is poor sleep and no exercise. However, if you’re keeping up with your training, you’ll blunt some of the negative effects of poor sleep (and as we’ll discuss in a moment, exercise may even help improve your sleep over time).
Take home? Different types of training have different responses to low sleep quality. Skill work and endurance take the biggest hit, while max strength holds up a little better. With that said, it’s still best to keep training as it protects us from many of the negative impacts of sleep loss.
How training and nutrition impact sleep
So far, we’ve looked at how sleep affects body composition and performance, but the relationship goes both ways. Behaviors like exercise habits or being in a deficit can also shape how well you sleep. Here are a few ways that show up in the research, and where small changes might help you sleep better.
Exercise and its effect on sleep
One of the cleaner relationships we see is between physical activity and sleep quality. For instance, low daily activity is often linked to worse sleep quality, and generally, people who engage in regular moderate-to-vigorous physical activity tend to report better sleep. A 2025 meta-analysis by Zhou et al looked at 81 randomized controlled trials and 6,193 participants and found exercise improved both subjective sleep scores and objective sleep efficiency. It was also noted that the longer someone kept to a consistent exercise schedule, the more it seemed to benefit their sleep.
Another 2025 systematic review and meta-analysis looked at adults with obesity and also found that exercise improved both sleep quality (and not so surprisingly helped with weight loss). In short, exercise does seem to help with sleep. That said, one thing to consider is timing. A recent review looked at the effects of evening workouts at different intensities and found that high-intensity workouts in the later evening could reduce REM sleep and possibly contribute to less sleep quality for some individuals. Note: More moderate or low-intensity exercise in the evening did not have the same effect.
Weight loss and its effect on sleep
When it comes to weight loss and sleep, the relationship isn’t always straightforward. As we’ve discussed, there’s strong evidence that low sleep quality can make it harder to manage your weight. The reverse (whether losing weight helps you sleep better) can be slightly mixed.
People with obesity or obstructive sleep apnea often see improvements in sleep after losing weight, especially when excess weight contributes to airway obstruction. We can literally lose fat in our neck, tongue, or surrounding airway structures. A recent review found that weight reductions were linked with improvements in the apnea-hypopnea index. So, if someone’s weight physically interferes with breathing during sleep, weight loss is a realistic aid.
For healthy individuals, it can get a little more complicated. Some studies have found that caloric restriction can improve sleep quality, but for others, it might actually disrupt sleep, especially if it leads to weight cycling. In short, you should consider the effect your weight loss could have on your sleep.
Take home? Losing weight could make a big difference for something like sleep apnea. However, caloric restriction itself is a mixed bag and seems to depend on more variables.
How to improve sleep (and make it work for you)
Sleep advice is a lot like fat loss advice in that it’s usually the boring stuff that works best. The goal here is to put together the pieces so you can take what’s useful, and apply it where it fits.
Decreasing sedentary behavior: As discussed, exercise is pretty beneficial for helping overall sleep quality. But even if you’re not participating in a formal training program, you’d likely benefit from decreasing too much consistent sedentary behavior and too long sitting stints. Try to do what you can to break up the day with walks outside and at least have some general step goals, as even low-impact physical activity could help sleep quality.
Sleeping extension: You could say a secret ingredient to sleep health is more sleep. Sleep extension is about creating a larger window of possibility for sleep, especially if you’re habitually getting fewer than your ideal hours at night. For most people, this involves going to bed earlier versus sleeping later, but either way works. Sleep extension can help with weight management and performance, so it’s a pretty solid choice.
I should note that sleep extension is not the same as “catching up” on sleep, where you use the weekend or a varied day of the week to catch up on sleep. While it’s better to get extra sleep where you can, that style of catching up on sleep isn’t the best choice for overall sleep health. It’s better to work on a consistent schedule.
Avoiding caffeine too late in the day: The tricky thing about caffeine is that everyone responds very differently. With caffeine, there is a range of half-life and periods that can affect sleep. For some, this can mean no caffeine, even 12 hours before bedtime. For others, they have way more leniency. It’s also good to test things for yourself because even if caffeine doesn’t affect sleep onset, it could still affect overall sleep quality. In short, test out your intake windows so you can find the best fit.
Naps: Like caffeine, naps affect people differently. For some, short naps (especially in the early to midafternoon) can boost performance, even if you’ve had a full night of sleep. For others, naps might interfere with nighttime sleep or leave you feeling groggy. The timing and length of naps seem to matter, with longer naps sometimes offering more benefit but also increasing the chance of sleep inertia. If you’re experimenting, starting with shorter naps (around 20–30 minutes) and leaving enough time between your nap and training session is a good place to start.
Constructive habits: While evidence is a little mixed across the board on the topic of sleep hygiene, there are some ideas (creating a repetitive bedtime schedule and reducing too much evening stimulation) that seem to work, especially when approached through the lens of habit formation. If you checked out our habit series, you know that triggers or environments can help you initiate behaviors without having to consciously act on them every time. What this means is something as simple as turning down the lights in your bedroom before you go to brush your teeth can start the process of getting you ready for bed. The more these cues occur in the same order and context, the more they become automatic and help you fall asleep.
Take home
I’m one of those who really believes your bed (and the whole vibe of your bedroom) is worth the effort. And to be clear, you’ve got to test what works for you, but if you’re making an active effort to make sleep a priority, you’re probably going to see some small benefit from that alone.
Lastly, a few tips:
Stick to a sleep schedule. Doesn’t have to be perfect, just consistent.
Watch the timing of your caffeine intake. For some people, that’s stopping at noon, and for others, it’s earlier.
Move more during the day. And if you can, walk outside during the daytime.
During your normal sleep hours, try adding a little more time (sleep extension). Even if it’s going to bed 30 minutes earlier, it can make a difference.
Use repeatable “winding down” cues. Start a bedtime routine of dimming the lights, brushing your teeth, opening up a book, or putting your sleep mask on your nightstand. Your body will start to notice.
Go for the tried-and-true “boring” solutions: Give an honest shot at the basic stuff before experimenting with less research-supported methods.
