To say that the relationship between sleep, eating and our weight is complicated is an understatement! More and more research is being carried out in this area. While numerous studies have shown that lack of sleep tends to increase calorie intake and weight, the reasons why aren’t yet clear.
Research recently published in the journal Nutrition and Diabetes saw that for each 30-minutes of sleep lost per day, we eat an average of an extra 83 calories. One possible reason for this is that lack of sleep alters levels of the hormones that control appetite – leptin and ghrelin – although not all studies have observed this.
Research published in the medical journal Sleep suggested that inadequate sleep increases the expression of genes related to weight gain, while other studies suggest that lack of sleep leads to impaired decision making or changes the way our brains respond to junk food.
How much sleep we need
Sleep experts suggest that between seven and nine hours of sleep is about right for most adults. Both too much and too little sleep has been associated with weight gain.
One of the main reasons why many of us lay awake at night is stress. Stress can impair sleep by increasing levels of the hormone cortisol, which is meant to peak in the morning just before we wake up.
This is exacerbated by some of the things we tend to use to deal with stress – high-caffeine drinks, a glass of wine, or late-night TV, for example. Drinks that contain caffeine (coffee, tea – even green, energy drinks) increase alertness, but individual tolerance levels vary. Meanwhile, the more alcohol you drink, or the more you watch TV or use a computer close to bedtime, the poorer your sleep quality tends to be.
The long-term effects of lack of sleep
Sleep and weight gain are inversely related. One large study found that adults who slept for fewer than five hours one and a half times more likely to be obese. In our deepest and most restorative sleep, blood pressure drops and our bodies get the chance to fully relax. At the same time, blood is driven to the muscles, providing nutrients for recovery and repair. Sleep is also known to regulate mood and help our brains function better, by improving learning and memory functions. So, long-term, lack of sleep can affect everything from skin health to mood. Disruption of the circadian system (our internal body clock) has also been associated with increased risk of cardiovascular disease.
Particular cravings associated with a lack of sleep
People who sleep less tend to have irregular meal patterns, choosing more high-fat and high-sugar foods and fewer portions of vegetables. One study at the University of California, Berkeley, found that sleepiness made complex decision-making more difficult – it might not be that we crave certain foods when we’re sleepy, just that we tend to pick the easiest option, which is often unhealthy convenience food!
Foods that rich in the amino acid tryptophan, such as milk, meat, fish, poultry, eggs, beans, peanuts and leafy veg, may help you to sleep better. It's converted in the brain to serotonin, the feel-good chemical that is then made into melatonin, which helps regulate the internal body clock. Carbohydrates also boost serotonin production – so serve a turkey, soybean and broccoli stir-fry with some brown rice for maximum impact.
In a study at Taipei Medical University, participants who ate two kiwi fruits an hour before bedtime saw an increase in average nightly sleep and an improvement in subjective sleep quality. This was thought to be because kiwi fruit is high in antioxidants and serotonin, but larger studies are needed to confirm the link. Kiwi fruit goes best in fruit salad, but works in savoury salads and salsas too.
Juice extracted from the tart Montmorency cherry is promoted for its sleep-enhancing benefits, but again there’s no firm evidence that it’s effective. It is naturally rich in melatonin, and one study at Northumbria University observed a significant increase in total sleep time and sleep efficiency with daily supplementation. It can be hard to get hold of tart cherries, but you can buy them dried to add to cereal, or in juice or capsule form.
Lastly, it’s important to remember that an active lifestyle can help you to sleep better and relieve other stresses. If you are struggling with sleep habits, try a good workout in the afternoon or early evening.