Sleeping and eating constitute some of a body’s most basic and necessary functions, and yet for people living across the globe they represent two of the largest concerns for maintaining health. A wealth of research evidence suggests that these two vital functions are linked, and that a disturbance in one can impact the other. As such, seemingly disparate conditions such as insomnia and obesity may be linked by underlying mechanisms.
Ethologists note that the body’s essential functions of sleeping and eating are in competition with each other because of how they are mutually exclusive. Otherwise put, short of receiving nutrients intravenously, it remains impossible for humans to eat and sleep at the same time. The conflict between these two interests comes to a head when an organism is deprived of both sleep and food. Experiments with rats have explored which need becomes more important to satisfy after a prolonged period of starvation and sleep deprivation. One study found that rats deprived of food spend an increasing number of hours awake. Even when they sleep, such rats experience a steady decrease in slow wave sleep (deep, non-dreaming sleep) and an even more precipitous decrease in their amounts of REM sleep. After about six to 11 days of starvation conditions, the rats no longer slept. After all sleep behaviors had disappeared the researchers re-introduced food to the rats and let them eat as they wanted. The rats that did not spontaneously eat this food died within 24 hours.
Other research studies have further confirmed the connection between sleeping and eating by examining how different energy sources affect one’s inclination or disinclination to sleep. While many will be familiar with this concept from examples such as falling into a “food coma” after a very large meal, a considerable body of evidence indicates that more so than the act of eating, what really impacts an animal’s circadian rhythm is the availability of easily-absorbed molecules to cells within the body. A study conducted in 1978 found that food-deprived rats that were given infusions of glucose after several days of starvation re-bounded back into the extended periods of sleep characteristic to rats that had dined only on normal food. They also noted that the effects of food deprivation on sleep varied according to the weight of the rat. Fatter rats experienced less dramatic alterations to their sleep patterns, presumably because their bodies had enough fat reserves that could be broken down and circulated in the bloodstream as an alternative source of energy.
Due to ethical reasons, experiments involving concurrent starvation and sleep deprivation in humans are out of the question. However observational studies of humans have confirmed a strong relationship between sleeping and eating habits in Homo sapiens as well. A longitudinal study of 60,000 women found that subjects that slept an average of five or fewer hours a night had a 15 percent greater risk of developing obesity than women who slept over seven hours per night. Other studies have found that sleep deprivation decreases the body’s sensitivity to insulin and consequently increases an individual’s risk for developing diabetes. Finally, yet more research has revealed that sleep curtailment causes dysregulation of a body’s appetite and sensitivity to satiation. Therefore, despite being two necessarily mutually exclusive biological imperatives, there is strong evidence to support the idea that a healthy living style must consider sleep and eating as two inter-locked functions.
By Sarah Takushi