Recent evidence suggests there is a link between sleep quality and weight control – poor sleep correlates with risk of obesity. The possible causal connection goes both ways. Obesity increases the risk for sleep apnea and other conditions that may interfere with sleep, such as back pain. Recent studies also suggest that sleep deprivation increases appetite and decreases energy ependiture. A recent review summarizes the evidence:
On this basis, the present review examines the role of sleepcurtailment in the metabolic and endocrine alterations, including decreased glucose tolerance and insulin sensitivity, increased evening concentrations of cortisol, increased levels of ghrelin, decreased levels of leptin and increased hunger and appetite. It will be discussed how sleeprestriction may lead to increase in food intake and result in greater fatigue, which may favour decreased energy expenditure.
All of the hormonal factors listed above would tend to increase hunger and fat storage and decrease satiety. Fatigue also decreases energy output. Resulting weight gain may further worsen sleep, leading to a vicious cycle.
A new study adds another element to the mix. Researchers looked at 23 healthy subjects over two sessions, one with normal sleep and one with sleep deprivation. They then exposed them to various food choices while in an fMRI scanner. They found that the sleep deprived subjects had decreased activity in their frontal lobes while making food choices.
This is a small and preliminary study, and fMRI data is very tricky to gather and analyze reliably. It also hasn’t been published but was presented at a scientific meeting. If we assume the results are valid, however, the study tells us two things. The first is that there is a difference in brain activity in the sleep deprived vs well rested state. This is not surprising, as optimal brain function is known to be highly sensitive to sleep deprivation. The other question the researchers were interested in, however, is what part of the brain is involved with food choices and sleep deprivation. It’s possible that there could have been increased activity in the more primitive centers of the brain that drive hunger, but that is not what they found.
The frontal lobes are involved in executive function, making complex strategic behavioral choices, such as which food to eat. We may be faced with many motivational factors simultaneously, such as hunger, the allure of our favorite foods, and also the desire to be healthy. The executive function of our frontal lobes is needed to balance these factors and come up with a final decision and act upon it. Avoiding tasty but unhealthful food takes a lot of mental energy, and those subjects who were sleep deprived had decreased mental energy. This means they are more likely to give in to their more basic urges rather than override them with their executive function.
Added to the prior research, and again assuming these results hold up, we can see that sleep deprivation causes a significant shift in the balance of factors that determine our behavior. We are more hungry and less able to modulate that hunger.
What do you do if you are trapped in this vicious cycle? It seems that we need further research to explore various approaches, but there are some common sense and evidence based approaches that will likely help. The first is to address sleep quality and duration. If that is the primary problem (such as sleep apnea) then the sleep disorder needs to be properly diagnosed and treated. Many of my patients have terrible sleep but do not volunteer that information or list it as a complaint, but when asked they relate having serious sleep problems. They simply did not consider it to be part of whatever complaints they were presenting with. If you have any sleep issues a reasonable first step is to see it as a problem and discuss it with your physician. They may want to order a sleep study and may be able to diagnose a specific problem.
Even without a specific underlying sleep disorder, many people can use improved “sleep hygiene” – basic methods of improving sleep quality and duration. These include things like not eating right before bed, avoiding caffeine, especially in the evening, and allowing for a sufficient winding down time before getting into bed.
In order to address the fatigue part of the equation, regular exercise is advised. Exercise has many documented health benefits in any case, and there is some research to support the conclusion that exercise improves sleep.
Because we are dealing with a complex interconnected physiological response, it is probably necessary to address many factors at once – overall eating habits, sleep quality, exercise, and any underlying conditions that may be affecting the quality of sleep or the ability to engage in physical activity. Further the research suggests that we need to consider the fact that maintaining healthy lifestyle habits is difficult. It takes a lot of mental energy, and there are factors that can decrease our mental energy and leave us vulnerable to poor decisions. It just takes a moment of sleep-deprived weakness to ruin a whole day of healthful eating.
This, perhaps, might be the biggest challenge, from both a personal and public health perspective. Part of the strategy of addressing the rising rates of obesity might be to make healthful eating decisions easier to make (requiring less of that frontal lobe mental energy). Some have suggested, for example, that perhaps it’s not a good idea from a public health perspective to ask every fast food customer if they want to supersize their order. We can preserve individual choice, but make the more healthful choices the default, low mental energy, pathway of least resistance. Make unhealthy choices take more mental energy and effort.
We also may want to consider the role of rationalization. This is where I think fad diets and many dieting products fail – they provide the illusion of eating healthy and make it easy to rationalize unhealthy behavior. Those low-fat cookies still have a lot of calories, but the “low-fat” on the label is very effective at short circuiting our executive function with denial and rationalization. Having restaurants print calorie content, for example, is likely an effective way to combat denial, and at least will help those who are paying attention.
We definitely need more research in this area to identify the optimal strategies for making healthful eating more common and to reverse the obesity trends in our society. I do think that taking a physiological and neurological view is helpful – identifying all the various factors that ultimately contribute to caloric intake and energy expenditure.