Sleep is like good nutrition for your brain. Poor sleep is like putting your brain on a junk food diet – literally. Now a growing pool of research is linking poor sleep habits and disrupted sleep patterns from shift work with adverse health problems that include obesity and metabolic conditions such as type 2 diabetes and heart disease. In this podcast, I’ll look at the sleep-health connection and explain what disrupted sleep could be doing to your food habits, hormones and weight.
The recommended sleep duration for adults is seven to nine hours a night, but many people often sleep for less than this. Research has shown that sleeping less than the recommended amount is linked to having greater body fat, increased risk of obesity, and can also influence how easily you lose weight on a calorie-controlled diet.
When it comes to weight loss, diet and exercise are usually thought of as the two key factors that will achieve results. However, sleep is an often-neglected lifestyle factor that also plays an important role.
One of the best-studied areas to do with altered sleep habits and health comes from studying people who do shift work. Shift work is becoming increasingly popular because of the high demand for flexibility and productivity in workforces in modern society. The flexibility of shift work though comes with a downside.
How strong the link between shift work and obesity was the subject of a recent scientific review which I’ll link to in the show notes. Shift work, in this case, was defined as where employees regularly switched between daytime and overnight schedules or worked exclusively overnight shifts. The review looked at 28 studies that explored the health impact of shift work. https://onlinelibrary.wiley.com/doi/abs/10.1111/obr.12621
The link between shift work and obesity was strong with up to a 30 percent higher risk of obesity seen for those that were regular shift workers. These same permanent shift workers were more likely to gain excess weight compared to people that alternated between day and night shifts. This points to the ongoing disruption of normal sleep patterns being particularly harmful.
And the review also found that it was not so much weight gain in general that was the biggest concern, but where that excess weight was found. In this case, there was more of the metabolically dangerous visceral fat found around the abdomen in people who routinely worked the graveyard shift.
So, why it is it do? Shift work is a challenge to the body’s natural circadian rhythm. The circadian rhythm is a 24-hour internal clock which cycles between sleepiness and alertness at regular intervals. Shift work creates a misalignment between the internal clock and the outside world. This can cause the body to secrete drowsy-inducing chemicals when you’re working or make you alert and awake when you’re trying to sleep.
Sleep duration also influences metabolism, particularly glucose metabolism. When food is eaten, our bodies release insulin, a hormone that helps to process the glucose in our blood. However, sleep loss can impair our bodies’ response to insulin, reducing its ability to uptake glucose. We may be able to recover from the occasional night of sleep loss, but in the long term this could lead to health conditions such as obesity and type 2 diabetes
Exposure to bright lights at night can compound the problem of shift work even more. Light exposure suppresses the production of melatonin – a key hormone that can regulate the production of other hormones such as insulin, cortisol and the hunger hormones leptin and ghrelin. Ghrelin stimulates your appetite while leptin decreases it. When you don't get enough sleep, ghrelin spikes and leptin levels stay low. The result? Your appetite goes through the roof because leptin isn't there to say, "Stop eating, you’re not hungry."
Showing how much alterations in these hormones and the circadian rhythm can be, researchers have previously conducted sleep laboratory experiments over 5 weeks where people had their sleep patterns disrupted and were slowly shifted to daytime sleeping and nighttime waking to mimic shift work. The reversal of the circadian rhythm caused a drop in metabolism. They also saw a fall in insulin by a third – making them less able to control blood glucose and even suppress appetite. And likewise, studies in people who were only allowed 4 hours of sleep find that they are much more likely to overeat the next day. That’s bad news for long-term weight gain.
Good sleep habits around shift work are vital. Shift work can be a challenge to healthy eating and exercise regularity. Shift workers should be even more aware of this and take healthy foods and snacks with them to work rather than rely on more limited options during the nighttime hours. Employers also need to take some level of responsibility and be flexible with schedules to avoid prolonged exposure to long-term night shift work for any single employee.
Altered sleep
Studying shift workers is a great model to look at the effects of sleep on metabolic health, but what about for what happens in people who have poor sleep habits in general and struggle to get a restful night’s sleep?
Disrupted and inadequate sleep is not just a problem for feeling tired and fatigued the next day. Changes in hormonal signalling, glucose metabolism, insulin sensitivity and levels of fatty acids in the blood have all been described in people with restricted sleep habits.
Most of the metabolic studies on sleep restriction have focused on glucose metabolism which is important for the risk of diabetes. How fat digestion and metabolism is affected is less clear. Addressing this, a study recruited 15 young healthy men to spend 10 nights in a sleep laboratory. After three nights of plenty of sleep in the lab, for the next five consecutive nights, they spent no more than five hours in bed. After this, they had two more nights of normal sleep. And I’ll link to the study in the show notes https://pubmed.ncbi.nlm.nih.gov/31484696/
How did the different sleeping patterns affect the metabolism of a high-fat meal? After four nights on the disrupted sleep protocol, participants found a standard high-fat meal to be less filling and satisfying than when they were fully rested. They also cleared the fat from their bloodstream quicker when sleep deprived. Having fewer feelings of fullness from a meal and clearing and storing fat quicker can combine to heighten the risk of weight gain.
Poor sleep patterns and inadequate sleep are a metabolic health hazard that can affect how the body metabolises carbohydrates and fats and even the feelings of fullness after a meal.
Junk food
And if you’ve ever wondered why a sleepless night can easily find you craving junk food the next day, science seems to have figured out just what is going on in the brain to drive this.
It is a common observation that people who do not get enough sleep, often start to favour energy-dense sweet and fatty foods - which is not so good for the risk of weight gain. Just why there is a connection between sleep deprivation and food preference has mystified scientists. One theory is that it could be because of a change in endocannabinoid production.
Endocannabinoids are neurotransmitters that act in the brain and the peripheral nervous system and have wide-reaching regulatory functions on memory, sleep and the immune system. Of greatest interest though is the effect of endocannabinoids on appetite and energy balance metabolism.
Endocannabinoids can change how the brain responds to smell with this sense tightly linked to how and what a person chooses to eat. Recent experiments show that in rodents, endocannabinoids enhance food intake by influencing the activity of the brain areas that processes odours.
So, what happens to endocannabinoid activity, smell and food preference in sleep-deprived humans? To answer this, a research team from the United States recruited 29 healthy men and women aged between 18 and 40 to take part in a sleep study. In a sleep laboratory, one group were given a normal night’s sleep and then 4 weeks later were only allowed 4 hours sleep. The second group had the sleep experience reversed with the sleep deprivation first followed by a normal night’s sleep 4 weeks later. The day after each sleep session, volunteers were served controlled menus for a full day of meals as well as a buffet of snacks. What and how much they ate was closely monitored. And I’ll link to this study in the show notes https://elifesciences.org/articles/49053
So, the big question: what happened? Food choices were very different after each of the sleep conditions. With sleep deprivation, more high-energy food options like doughnuts and chips were eaten. Blood levels of endocannabinoids were also higher after sleep deprivation and this increase was related to changes in food choices.
To round out the experiment, people also underwent a functional MRI scan before the buffet to look at brain region activation. Food smells were wafted to the participants while being scanned. They then were presented with several different food and non-food odours. For sleep-deprived subjects, activity in one part of the brain called the piriform cortex differed the most between food and non-food odours.
The piriform cortex communicates with a part of the brain called the insular cortex and in sleep-deprived subjects, the connection between the two regions was impaired. This is important because the insula regulates food intake related to smell, taste and how much food is in the stomach. So, sleep deprivation could be a marker for lack of stimulation of these brain regions which leads to a desensitised smell response or faulty energy balance signalling.
Sleep deprivation is never a good thing and now science shows how it can change the brain to make it more tuned to enticing food smells from high-energy junk food. So apart from getting more sleep, it is worth paying attention to the faulty signals that the brain may be sending for highly desirable food and keeping some distance from the enticing smells.
Getting a good night’s sleep is easier said than done especially if you’re battling insomnia, stress or maybe even a new parent, but it is vital to have the foundation of good sleep habits in place to give yourself the best chance. And these fundamentals revolve around:
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.