We know that there’s a relationship between obesity and sleep deprivation, but is it the extra weight that causes sleep problems or does the poor sleep make you fat? Well, it’s actually both. It’s a complex relationship, and one we’re going to explore today.
For people with a high BMI, there’s a correlation with sleeping later than normal (both going to bed and waking up late) and a shorter sleeping time overall. Although there are discrepancies in the norm (some people lose weight when they don’t sleep enough), the majority of the population will have a direct correlation between less sleep and added fat.
In many studies, we’ve been able to discover that long periods of shortened sleep will also lead to cardiovascular disease and insulin resistance. Why? When we lack sleep, we suddenly desire foods that are high in calories and carbohydrates. This pattern has been proven; thanks to advanced medical imaging scans, we see that the area of the brain linked with appetite is more active in people who sleep less.
The deeper picture is more complex, however. In some studies, the subjects still gained weight despite no notable difference in appetite. Could it be the foods we choose to eat? While one night of poor sleep may leave you wanting to eat more, a second night may change what you eat. For example, you may look for quick resolutions to your hunger through cake and chocolate as opposed to healthier options of fruit and vegetables.
At the moment, we’re in the middle of an obesity crisis and there’s two sides to the problem;
- Consuming too many calories
- Not burning enough calories through exercise
Unfortunately, both of these factors are affected when we lack sleep. When tired, we’re less inclined to exercise (and we also fidget less). Furthermore, we can’t ignore the hormones.
The Role of Hormones
Leptin and Ghrelin
Our bodies are incredibly clever; the fat cells (adipocytes) release leptin. Once it hits the bloodstream, it’s basically informing the mind that there’s sufficient fat stores and suppresses the appetite. On the flip side, the stomach will release ghrelin when empty…and then we eat. We’ve simplified this a little and scientists will tell you that those who are obese will tend to have higher ghrelin levels.
Regardless, the problem with sleep deprivation is that it pushes up the ghrelin levels and suppresses the leptin. Suddenly, the brain thinks the body is starving and that we need to eat. According to some experts, four hours is the magic switching point. If we get less than four hours of sleep in a night, the blood plasma will have higher levels of ghrelin and lower levels of leptin.
Just like the sleep circadian cycle, leptin actually follows a circadian rhythm. Instead of being tied to day and night, however, it’s more correlated with habitual meal patterns. Also, the amount of exercise you perform will decrease leptin levels.
Our sleep patterns are affected by the corticotropin-releasing hormone and growth hormone-releasing hormone (GHRH) and how these two interact. Also, sleep is promoted by two particular hormones; Neuropeptide Y and Galanin.
More recently, we’ve learned about the hypocretin (orexin) system in the hypothalamus. As we know, the release of leptin regulates appetite and informs the brain of energy levels in the body. In turn, leptin release is affected by the levels of orexin. Though scientists have tried to stay on top of these interactions and how/why they occur, they’ve been unable to understand all of them just yet.
Within the body, there are several cycles and systems that seem to compete. In the future, we hope that a better and deeper understanding of hormones will allow for treatments to be discovered for sleeping problems. Since sleep and weight have a direct relationship, this could also lead to improvements in the obesity crisis that so many specialists are concerned about in the Western world.
There is cause for hope and recently scientists are working closer with orexin. After noticing how it interacted with leptin, there was excitement that this correlation could become a therapy opportunity in the future. By increasing orexin levels, we could assist leptin release and help people who are obese.
People who suffer with sleep deprivation are well aware that this condition leads to drowsiness and fatigue the next day (low energy levels); which leads to less exercise. As we’ve already seen, it also causes a larger appetite than normal and we find ourselves craving fatty foods. So, it’s almost a double effect; we’re exercising less and eating more.
Biologically, evolution leads to us to store more fat in the summer in preparation of the colder months ahead. With short nights and long days, we sleep less, and these circadian signals might lead to the body storing more fat.
Thankfully, the hard work of scientists has allowed us an answer to most questions. For example, we know that the circadian clock controls certain genes that regulate the sleep-wake clock; these same genes impact fat deposits too.
Using genetic engineering, researchers managed to switch off this clock gene in mice and they didn’t gain weight…even when placed onto a high calorie diet compared with a control group. With a disruption in the glucose and lipid metabolic pathways, the mice in the first group (genetically modified) didn’t store anywhere near as much fat as the second group (control).
Released by adipose tissue and called adipokines, visfatin and leptin are both hormones that are higher in people with a risk of diabetes (i.e. have high insulin resistance). In a study, sleep deprivation was shown to increase the blood levels of the hormones. While leptin increased by 6%, the jump was higher for visfatin at 14% (PER HOUR of lost sleep).
Note: Retinol-binding protein 4 is another adipokine thought to influence insulin resistance, and there was no change here with sleep deprivation.
With all of this information, the link between craving foods high in fat and a disrupted circadian rhythm is only growing stronger (this has even been quoted "reports scientists have found in Nature magazine).
What about when stress levels are high? The body may just react differently during these times; when stress is to blame for sleep loss, the increase in calorie consumption is thought to be higher. We now commonly refer to this craving as ‘comfort food’.
Impact on Child Obesity
After the results of a British study were published, a link between time spent in the stage 3 and REM sleep and weight was established. Those kids who were moderately overweight spent more time in REM sleep and deep sleep. Yet, kids under the ‘obese’ classification had their REM sleep and deep sleep cut short.
Elsewhere, research has also brought up connections between sleep loss and insulin sensitivity in children.
Eating and Sleeping Correctly
If we needed further proof of the relationship between diet and sleep, we only need to look at eating habits that don’t conform to the ‘norm’. As a child, were you ever so naughty that you were forced to bed without dinner? If so, you’ll know how tricky it is to sleep with an empty stomach.
During Ramadan, the eating and drinking times of Muslims are confined to specific periods of the day. As a result, sleep latency increases while slow-wave sleep and REM sleep decrease. When body temperature fluctuations shift, this also indicates a shift in the circadian cycle. In another study, total sleep time and non-REM sleep stayed the same while REM time reduced.
Again, this is something that has been shown with mice. After adjusting their diet and time of eating, their circadian cycle was directly affected. However, we should note that the researchers couldn’t determine the importance of fat percentage in the diet, whether the mice were eating when they would normally sleep, or the molecular mechanism for this change.
Short-Term vs Long-Term Trend
Of course, it’s impossible to prove cause and effect just because many sleep-deprived people are obese (and vice versa). For doctors, there was much debate as to whether they should be intervening to get people to sleep more. Either way, the evidence that sleep duration is directly affected by metabolic hormone levels is only getting stronger.
While some scientists are hesitant, others look towards long-term trends to support the cause and effect idea. For example, over the past 100 years or so, average sleep duration has decreased. Across the last 40 years, obesity rates has grown, and average BMI has followed suit.
Can we make the jump from individuals to a whole society? To provide an insight to the other side, some will say that the decrease in sleep times are insignificant. Moreover, obesity can be a result of many other problems; for one thing, the increased machinery and automation in the workplace has led to a fall in demand for human muscle. For another, the fact that junk food is so cheap and widely available.
Whether clear evidence or sheer coincidence, many are still calling for people to correct their sleeping patterns to sleep more. For researchers, they’re pushing for more studies to learn more.
Despite this, many people are still skeptical, and this includes Jim Horne, a revered sleep scientist. He says that the link between weight gain and a lack of sleep is too thin and that sleepiness-related accidents are the more prominent concern for this new trend of sleep deprivation. Although he agreed that getting less than four hours in a night would affect glucose intolerance, he also stated that the ‘short sleeper’ quality would only be found in a small percentage of the obese people.