How do sleep, stress and mental health affect weight?

How does sleep affect appetite and weight?

Too little sleep increases hunger and makes high-energy foods more tempting. The US National Institutes of Health advise adults aged 18 to 64 to aim for 7 to 9 hours of sleep a night, and adults over 65 for 7 to 8 hours.

In a well-known laboratory study, healthy young men slept only four hours a night for two nights. Their leptin, a hormone that signals fullness, fell by 18%. Their ghrelin, a hormone that stimulates hunger, rose by 28%. They reported 24% more hunger and a stronger appetite for sweets, salty snacks and starchy foods. Being tired also makes it harder to be active and to plan meals.

Large population studies find that people who regularly sleep less are more likely to live with obesity, in both children and adults. These studies show a link but cannot fully prove cause and effect. The relationship also runs the other way: obstructive sleep apnoea, which is common in people living with obesity, disturbs sleep. Read more about health risks of obesity.

Shift work and night work

Working night shifts is linked to a higher risk of obesity, especially fat around the belly. A meta-analysis of 28 studies found that night shift work was linked to a 23% higher risk of overweight or obesity. People working permanent night shifts had a higher risk of abdominal obesity than those on rotating shifts.

Night work disrupts the body clock, which helps regulate appetite and how the body processes food. It also shortens sleep and makes regular meals and exercise harder. These are working conditions, not personal choices, and employers can help by planning shifts carefully and offering healthy food at night.

How do chronic stress and cortisol affect weight?

Long-term stress can contribute to weight gain through the stress hormone cortisol and through changes in eating, sleep and activity. Short bursts of stress are normal. But when stress goes on for months, for example because of money worries, caring duties, discrimination or an unsafe home, the body stays in an alert state.

Cortisol can increase appetite, especially for energy-dense food, and may favour fat storage around the abdomen. Very high cortisol levels, as in the rare condition Cushing's syndrome, cause marked weight gain. Studies that measure cortisol in hair, which reflects levels over several months, have found higher cortisol in people living with obesity.

Weight stigma is itself a source of chronic stress. In a large English study, people who reported weight discrimination had higher hair cortisol, and this partly explained the link between obesity and cortisol. Read more about weight stigma and its effects.

How are depression and weight linked?

Obesity and depression each increase the risk of the other. A meta-analysis of 15 long-term studies with 58,745 participants found that obesity increased the risk of developing depression by 55%. Depression increased the risk of developing obesity by 58%.

Depression can change appetite, sleep and energy, and some antidepressants can cause weight gain (see medication and weight gain). In turn, living with obesity can bring stigma, physical health problems and low self-esteem, which raise the risk of depression. Treating both together usually works best.

Trauma and adverse childhood experiences

Difficult experiences in childhood, such as abuse, neglect or growing up with violence, are linked to a higher risk of obesity later in life. A meta-analysis of 41 studies with more than 190,000 participants found that people who were maltreated as children had about 36% higher odds of obesity.

Possible reasons include long-term changes in the stress system, using food for comfort or a sense of safety, disturbed sleep and depression. Care that takes past trauma into account, without judgement, is more likely to help. You never have to share your history to get good care, but it can help your care team understand your situation.

Binge eating disorder

Binge eating disorder is a treatable eating disorder in which people regularly eat a very large amount of food in a short time and feel a loss of control. Unlike bulimia, binges are not followed by vomiting or other ways to compensate. It is often accompanied by shame and distress, and it is more common in people living with obesity.

Strict dieting can sometimes make binge eating worse. Psychological treatments, such as cognitive behavioural therapy, are effective. If this sounds familiar, talk to your doctor and read about psychological support.

Which practical steps can help?

Small, steady changes to sleep and stress can support your health and make other treatment easier.

• Protect your sleep: keep regular bed and wake times, limit screens and caffeine in the evening, and keep your bedroom dark and cool.
• If you work shifts: plan your main meals at regular times, take healthy food with you, and protect your sleep after night shifts with a dark, quiet room.
• Look after stress: regular movement, time outdoors, relaxation techniques and contact with people you trust can all help.
• Ask about snoring: loud snoring, breathing pauses or daytime sleepiness can be signs of sleep apnoea, which can be treated.
• Talk about mood: if you feel low, anxious or out of control around food for more than a couple of weeks, tell your doctor.
• Be kind to yourself: self-criticism adds to stress. Progress is rarely a straight line.

Your doctor can check for sleep problems, depression and eating disorders and refer you for support. Our doctor visit checklist can help you prepare.

If you have thoughts of harming yourself, contact your local emergency number or a crisis helpline straight away.