Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Struggling with sleep? It might be affecting your weight more than you think. Insomnia, marked by restless nights, frequent awakenings, and relentless fatigue, does more than leave you feeling drained. It can throw off your metabolism, disrupt appetite signals, and lead to unexpected weight changes. Some people find themselves gaining weight, while others experience unexplained weight loss.
But why does this happen? In this article, we will explore the causes and symptoms of insomnia, its effects on the body, and the science behind these surprising changes. Keep reading to find out how your sleep (or lack of it) might be shaping your body in ways you never expected.
Ever found yourself staring at the ceiling, willing yourself to fall asleep? Insomnia can be more than just an occasional restless night—it often has deeper roots. From stress and anxiety to lifestyle habits and medical conditions, several factors could be keeping you awake.
Stress and Anxiety: When your mind won’t switch off, neither will your body. Racing thoughts, worries, and heightened alertness can make it nearly impossible to fall or stay asleep. Research suggests that some people are especially sensitive to stress-related sleep disruptions, making insomnia a long-term struggle.
Poor Sleep Habits: Late-night screen time, erratic sleep schedules, frequent naps, or an uncomfortable sleep environment can all confuse your body's natural sleep-wake cycle. Without good sleep hygiene, your body may not recognise when it’s time to wind down.
Medication Side Effects: Some medications, including antidepressants, stimulants, and corticosteroids, can interfere with your ability to sleep. Even common substances like caffeine, nicotine, and alcohol can throw off deep sleep cycles, making insomnia worse.
Neurological Problems: Conditions, such as Parkinson’s disease, Alzheimer’s, and restless leg syndrome, can disrupt the brain’s ability to regulate sleep, leading to chronic insomnia.
Difficulty Falling Asleep: Lying in bed for long periods without being able to drift off is one of the most common signs of insomnia.
Waking Up Frequently During the Night: Even if you manage to fall asleep, frequent awakenings can prevent you from getting deep, restorative rest.
Waking Up Too Early and Not Being Able to Go Back to Sleep: Waking up hours before your alarm and struggling to fall back asleep can leave you feeling unrested.
Feeling Tired Upon Waking: A full night's sleep should leave you refreshed, but insomnia often leads to grogginess and a lack of energy in the morning.
Daytime Fatigue or Sleepiness: Poor sleep can result in excessive tiredness during the day, making it difficult to focus or stay productive.
Irritability or Depression: Lack of sleep can affect mood, leading to increased irritability, anxiety, or even symptoms of depression.
Yep, struggling to sleep can mess with your appetite. When you’re sleep-deprived, your body produces more ghrelin (the hormone that makes you hungry) and less leptin (the hormone that signals fullness). The result? You’re more likely to crave high-calorie, carb-heavy foods.
Research backs this up. A study found that just one night of bad sleep can increase ghrelin levels by 15% and drop leptin levels by 16%. Over time, this hormonal shift can lead to overeating and weight gain, making good sleep just as important for appetite control as diet and exercise.
Lack of sleep doesn’t just affect energy levels—it impacts nearly every system in the body.
Insomnia slows cognitive function, affecting memory, concentration, and decision-making. Chronic sleep deprivation can also increase the risk of anxiety and depression.
Sleep is crucial for immune function. Poor sleep weakens the immune response, which makes you more susceptible to illnesses.
Insomnia can worsen existing respiratory conditions, such as asthma and sleep apnoea, leading to further sleep disturbances.
Sleep deprivation affects digestion and can lead to imbalances in gut bacteria, potentially influencing metabolism and weight changes.
Lack of sleep increases the risk of high blood pressure, heart disease, and stroke due to increased stress on the heart.
Disruptions in sleep affect hormone production, including those regulating stress, metabolism, and appetite.
While insomnia is often linked to weight gain, it can also contribute to weight loss in several ways.
Insomnia can reduce hunger signals, leading to lower food intake. Stress and fatigue can also suppress appetite.
Some people with insomnia engage in late-night physical activity or pacing, which can lead to higher calorie expenditure.
Sleep deprivation increases the body’s resting energy expenditure, meaning you burn more calories even at rest.
Insomnia disrupts metabolism, causing the body to use energy inefficiently and sometimes leading to weight loss.
Chronic stress from insomnia increases cortisol levels, which can lead to muscle breakdown and unintentional weight loss.
Not getting enough sleep can throw your body out of balance, and weight is often caught in the middle. Some people lose weight due to insomnia, but for others, it leads to weight gain. One reason is appetite. Sleep deprivation increases hunger hormones, making high-carb and sugary foods more tempting. It also saps your energy, which means less movement and fewer calories burned.
Metabolism takes a hit too. Research found that sleep-deprived individuals burn fat less efficiently and lose more lean body mass instead. This imbalance in energy use could make it harder to manage weight, so if the scale is creeping up, your sleep schedule might be a hidden factor.
Improving sleep quality can help regulate weight and overall health.
Going to bed and waking up at the same time every day helps regulate your body’s internal clock.
A cool, dark, and quiet room improves sleep quality. Invest in a good mattress and pillows for better comfort.
Blue light from screens can disrupt melatonin production, making it harder to fall asleep. Try reading or listening to calming music instead.
A warm bath, meditation, or deep breathing exercises can signal your body that it’s time to sleep.
Caffeine can stay in your system for hours, and large meals can cause discomfort, making it harder to sleep.
Physical activity promotes better sleep, but intense workouts too close to bedtime can be stimulating rather than relaxing.
Looking for more tips to fall asleep quickly? Click here.
Insomnia affects weight in complex ways. It can also lead to both weight loss and weight gain, depending on how it impacts appetite, metabolism, and energy expenditure. While some lose weight due to a decreased appetite and increased energy use, others experience weight gain from hormonal imbalances and cravings. Prioritising good sleep habits can help restore balance and improve overall well-being.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.