Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Even when your diet is on point and your workouts are consistent, the numbers on the scale can plateau. One often-overlooked factor? Sleep.
Research shows that insufficient sleep can disrupt hormones, slow metabolism, and increase fat storage, making it harder to shed pounds. In one study, adults who slept only 5.5 hours a night lost less fat than those who got 8.5 hours, even when both groups consumed the same calories.
Getting enough rest can make a real difference in how your body loses weight. Here’s how poor sleep affects your body and what you can do to turn it around.
Sleep and metabolism are tightly linked. While you sleep, your body balances hormones, repairs tissues, and regulates blood sugar, all key players in weight management. Poor or insufficient sleep disrupts these processes, leading to slower calorie burning and a stronger tendency to store fat. According to studies, chronic sleep deprivation can decrease your resting metabolic rate and impair glucose tolerance, making it harder to use energy efficiently.
Put simply, when you skimp on sleep, your body shifts into ‘energy conservation mode,’ slowing metabolism and making fat loss harder. For more information about the connection between sleep and weight, see Can Sleeping Help You Lose Weight?
When you’re running on little sleep, it’s not just your mood that takes a hit. Your entire weight loss process gets derailed.
Lack of sleep messes with two major appetite hormones. Ghrelin, the ‘hunger hormone,’ increases, while leptin, the hormone that signals fullness, decreases. This imbalance tricks your brain into thinking you’re hungrier than you really are.
Sleep-deprived brains crave quick energy, usually in the form of sugary, fatty foods. Research found that poor sleep enhances activity in the brain’s reward centre, making junk food more tempting.
Cortisol, the stress hormone, naturally rises when you don’t sleep enough. Elevated cortisol is associated with increased visceral fat, the stubborn kind around your belly. A journal study found that even one night of poor sleep can trigger noticeable hormonal changes the next day, including an afternoon spike in cortisol, which may affect metabolism and appetite.
When you’re tired, your body burns fewer calories at rest. Even short-term sleep restriction reduces your body’s ability to convert food into usable energy efficiently.
Less sleep means less motivation to move. Fatigue makes it harder to exercise, and you’re more likely to skip workouts or underperform during them, cutting into your calorie deficit.
Inadequate sleep causes insulin resistance, which means your body struggles to manage glucose. Over time, this can lead to weight gain and increase your risk of type 2 diabetes.
Your gut microbiome, crucial for digestion and metabolism, also suffers from poor sleep. Disrupted sleep can alter gut bacteria balance, making it harder to process nutrients and control appetite.
Poor sleep raises inflammation and fluid retention, making you feel puffy or bloated. You may not actually gain fat, but the scales might creep up due to water weight.
If you’ve been doing everything right but still aren’t seeing results, your sleep might be the culprit. Look out for these signs:
Constant fatigue and low energy
Intense cravings for sugary or salty foods
Difficulty controlling appetite
Weight plateau despite healthy habits
Unexplained weight gain
Mood swings or irritability
Trouble staying consistent with workouts
Increased belly fat or bloating
Even one or two of these signs can suggest that your body’s recovery and metabolism aren’t getting the rest they need.
According to the American Academy of Sleep Medicine and the Sleep Research Society, adults should aim for 7 or more hours of sleep per night on a regular basis to promote optimal health. Here’s what the research highlights:
Adults should sleep at least 7 hours per night to support healthy metabolism, hormone balance, and recovery.
Sleeping less than 7 hours regularly is linked to:
Weight gain and obesity
Diabetes and insulin resistance
Hypertension, heart disease, and stroke
Depression and mood disorders
Impaired immune function and increased inflammation
Reduced performance, concentration issues, and higher accident risk
Sleeping more than 9 hours per night may be suitable for:
Young adults
Those recovering from sleep debt
Individuals with illness or high physical demands
For most adults, consistently sleeping 7–9 hours is ideal for maintaining healthy body weight and overall wellbeing.
Healthy sleep isn’t just about duration. It also depends on:
Quality: Deep, uninterrupted rest
Timing: Sleeping at consistent hours each night
Regularity: Keeping a steady sleep–wake cycle
If you’re regularly sleeping too little or too much and noticing weight or mood changes, consider discussing it with a healthcare provider to rule out sleep disorders or underlying health issues.
Good sleep hygiene can be a powerful weight loss tool. Here’s how to get the most out of your nights:
Stick to a consistent sleep schedule – Go to bed and wake up at the same time daily, even on weekends.
Avoid late-night caffeine and alcohol – Both interfere with deep, restorative sleep.
Limit screen time before bed – The blue light from screens suppresses melatonin, your sleep hormone.
Create a cool, dark, and quiet sleep environment – Ideal sleep temperature is around 18–20°C.
Try relaxation practices like meditation or stretching – Calms your nervous system and lowers cortisol before bed.
Keep evening meals light and balanced – Avoid heavy or spicy food close to bedtime.
Get regular physical activity during the day – Exercise promotes better sleep quality and helps regulate hormones.
If you’re sleeping fine but still not seeing results, your stress levels might be the underlying culprit. Read How Stress Hormones Affect Weight Loss to learn how cortisol can stall your progress.
Sleep is more than rest. It’s when your body recovers, balances hormones, and fine-tunes metabolism. Skipping it leaves you tired and can slow down fat loss. Prioritising quality sleep helps your diet and exercise work more effectively, making weight loss smoother, more sustainable, and healthier.
So before you cut more calories or double your workouts, ask yourself: am I sleeping enough? Sometimes, the best fat-burning strategy starts with turning off the lights a little earlier tonight.
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.