Canadian researcher Jean-Philippe Chaput concluded a five year study demonstrating that insufficient sleep predicted the likelihood obesity and overweight more closely than either the amount of exercise or caloric intake.
This surprising result flies in the face of standard advice for overweight people to “exercise more and eat less.” It is generally recognized that we are now sleeping 20-25% less than even two generations ago, and since sleep debt is cumulative we are in effect skipping more than a full night’s sleep every week.
In fact, a meta-analysis of 89 longitudinal and prospective research studies showed that 81 of the published papers demonstrated a positive correlation between sleep debt and weight regulation disturbances.
This is not necessarily intuitive, so it is worth looking at the many reasons that play into this effect:
Sleep debt reduces metabolic activity. When you are more tired, you are less likely to engage in physical activity. More subtly, sleep debt also changes the amount of energy a person burns in fidgeting or holding one’s posture.
Perhaps even more significant is impaired cognition when tired, such as reduced diligence and alertness. In a distracting or stimulating environment, it’s hard to know when a person has eaten enough, and sleep debt makes it harder to notice those signals. Researcher Christian Benedict took FMRI (functional magnetic resonance imaging) of people’s brains when shown high-calorie and low-calorie foods, and in the condition of sleep deprivation the anterior cingulate cortex responded differently. This is part of the frontal cortex that processes emotional decision making, and sleepy people gravitated toward higher calorie food choices.
Sleep deprivation also reduces impulse control. We make 200 or more food related decisions every day. Someone who has not slept enough has less inhibitory control over their impulses. If one is tired there is an increased tendency to simply grab something appealing and convenient rather than considering what might be in one’s best interests. Additionally, a tired person feels less motivated to prepare nourishing meals.
At a most basic level, sleep deprivation directly alters hormones that trigger the sense of hunger as well as other metabolic activities such as regulating blood sugar levels and the processing of body fat.
The cumulative effects of these many effects resulted in findings that sleep deprived people ate an average of 300 calories more per day than rested people. In some of the studies sleep deprived people reported more hunger, but in many studies tired people did not perceive themselves to be any hungrier than in sleep satiated conditions. Nevertheless they ate more and digested it less efficiently. Sleep deprivation alone would account for a weight gain of approximately a pound every ten days, or around 35 pounds a year.
So if you are concerned about regulating your weight and managing your fitness, you might just be better off getting to bed earlier tonight…and tomorrow night as well.
Human Fitness tip: If you need an alarm to wake you up in the morning, you are probably not getting enough sleep. In general, a person wakes when rested, and by definition an alarm wakes you before you wake up on your own. Adjust your bedtime until you reliably wake at the time you need for your morning routines. Assuming that you are currently carrying a sleep debt, it may take a while of extra sleep in order to burn down your deficiency and discover the amount of sleep that you normally require each night.