The health and weight impact of your circadian rhythm
Anyone who has attended a school band concert understands how awful it is to be out of rhythm. Like a good beat, the human body seems to thrive when steady lifestyle patterns and routines are followed. When daily habits are predictable and regular, the body anticipates and prepares for certain stimuli on a rhythmic basis. Because these rhythms seem to have a frequency of about 24 hours (“circa diem” meaning “about a day” in Latin), they are often referred to as circadian rhythms. These rhythms play a key role in managing the function of vital organs in our bodies (including the heart, lungs, pancreas, and adipose tissues) through hormone and nervous control. When these biological and chemical rhythms are established and maintained, the organ systems work in a more synchronized style, which provides an optimal environment for health and healing. When irregularity alters these rhythms – a term known as chronodisruption – increased incidence of cardiovascular disease, metabolic syndrome, ageing, and even some forms of cancer  are observed.
Let’s discuss how sleep, diet, and exercise each influence circadian rhythm and how these impact metabolic health and weight management.
Circadian Rhythm and Sleep
With industries such as healthcare, manufacturing, and transportation requiring continuous operation, it is estimated that nearly one fourth of the worldwide population works either a swing shift or a night shift. Add to this a growing population of 24/7 technology addicts, video gamers, a growing night life industry, and demanding work/school/social life balance and it quickly becomes evident that much of our population is more than willing to sacrifice sleep for work or pleasure without recognizing the impact on their metabolic health  and immune system.
Studies that intentionally cause sleep deprivation have observed plasma glucose levels increase by 20-30% and that insulin sensitivity decrease by 20%. Not surprisingly, circadian rhythms and their effects on metabolism are not only dependent on sleep quantity, but on sleep consistency as well. While it is recommended that most adults get between 7 and 9 hours of sleep each night , getting that sleep in the same routine is one modifiable risk factor that can lead to improvement in several health indicators. In fact, regularly shifting a sleep schedule by an hour is associated with a 41% increase cardiovascular disease, a 14% increase in type 2 diabetes, and a 63% increase in BMI compared to a consistent sleep group.
In addition to the impacts of sleep on circadian rhythm and its influence on metabolism, the circadian system also exerts a strong influence on immune functions. The body adapts over time to be most efficient according to a 24 hour sleep-wake cycle with differentiated immune cells (like natural killer cells) peaking during the waking hours to contest specific antigen exposure which is more likely during the waking hours of the day. Undifferentiated cells (like memory T cells) peak at night to fight slower, more general antigens. When sleep is curtailed or asynchronous, pro-inflammatory cytokines are released and a low-grade inflammation is present.
Circadian Rhythm and Diet
The brain sends signals to eat during the light hours and abstain from food during the dark hours. The gastrointestinal system anticipates these cycles of eating and fasting and establishes its own circadian rhythm of hormone and enzyme production to digest and absorb our foods. For example, hormones that help produce peristaltic contractions, such as motilin and gastrin, are produced in the anticipation of moving food down the pipeline. If this circadian physiology is disrupted, these hormones and enzymes produce their actions at inappropriate times. This may ultimately result in various GI disturbances or diseases such as irritable bowel syndrome, gastroesophageal reflux disease, non-alcoholic steatosis hepatitis, and peptic ulcers.
Meal timing and its relationship to weight gain has also been a popular topic of scientific debate. An overwhelming number of reports suggest that eating most of ones calories earlier in the day is more in sync with circadian rhythm and allows for better utilization of the calories throughout the day, leading to a lower BMI compared to those who eat more calories later in the day.[16-18] Early eating changes patterns in cortisol and the expression of several circadian clock genes which results in lower 24-hour glucose levels and enhanced lipid metabolism. This evidence supports the notion that eating in a regular pattern and keeping calories stacked towards the beginning of the day can provide circadian synchronization and its associated benefits.
Circadian Rhythm and Exercise
Like patterns of sleep and eating, exercise can act as an influencer on circadian rhythm. Beyond its benefits of developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness, exercise performed in a regular routine boasts additional benefits because of its ability to synchronize peripheral and central circadian rhythms.[20-21] However, humans are unique from other animal species because we voluntarily shift activity phases to abnormal times of day, causing a misalignment between our activity period and our internal circadian clock.
It is well established that physical performance, VO2 max, and body temperature are all elevated later in the day. In terms of circadian rhythm, this means that exercising later in the day, according to personal chronotype (how early or late your body elevates these levels) will improve physical performance.
The body thrives when it receives internal and external cues in regular patterns so that it can anticipate and prepare for certain stressors appropriately. Sleep is a major contributor to circadian rhythm and is mediated by both the amount of sleep and the consistency in sleep timing. When adequate sleep is achieved on a regular basis, blood glucose, insulin resistance, immunity, and inflammation all improve. Eating later in the day increases the risk of weight gain and chronodisruption which may lead to irritable bowel syndrome, gastroesophageal reflux disease, non-alcoholic steatosis hepatitis, and peptic ulcers. Finally, circadian rhythm is influenced by exercise and studies suggest that physical performance, VO2 max, and body temperature are all elevated later in the day and that this is when the body is most primed for physical activity according to circadian signals.
Ultimately, maintaining regular patterns in diet, exercise and sleep will contribute to a synchronized circadian rhythm and a better environment for health and healing. This is especially difficult in our society when international travel, demanding work deadlines, abundant social activities, and other demands regularly change our sleep patterns, dietary habits, and exercise routines. No one is perfect but achieving and maintaining your life in a rhythm might be what you need to get out of a rut and on to achieving the next level of your best health.
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This article is for informational and educational purposes only. It is not, nor is it intended to be substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice.