Last month we learned about the need to space out our meals to allow the digestive system a time of rest. We also learned that our digestive system works over a period of many hours to days, to digest our food, and to eliminate the waste, thus the focus was on the timing of our meals based on the length of the process of digestion, especially taking into consideration the amount of time that our food remains in our stomach. We also learned that the length of the digestive process also depends on the types of foods we eat. However, there is another very important timing to consider, and that is the way the whole body responds to the timing of our meals over a 24-hour period. We need to be mindful of our meals throughout the day.
I was planning to continue discussing the importance of the timing of our meals, and then my research led me to consider, not only the importance of the timing of our meals in terms of our digestive health, but how our whole body runs on an internal time clock, with implications beyond just our digestion system. Therefore, I decided to segue into a look at our body’s internal clock, also known as the circadian rhythm. An understanding of our body’s circadian rhythm will better explain the reasons for the timing of our meals and how they impact our overall health.
Our bodies run on a 24-hour circadian rhythm; it is an internal clock, which determines how our physical and mental states, our mood, and behavioural patterns change over a 24-hour period. These patterns include body functions such as our sleep-wake cycle, immune function, digestion, alertness, hormonal activity, and body temperature. This internal clock is not governed by any external factors; it occurs naturally in humans, as well as in other animals, plants, and microbes. Even without external influences, our circadian rhythm follows closely to a 24-hour period. How marvellous is God’s wisdom, to create man so intricately in tune with the rest of nature!
In their findings published on June 11, 2020, in The Journal of Clinical Endocrinology & Metabolism, the researchers say eating late could promote obesity if these conditions happen often enough.
“What time you eat could be just as important as what you eat when it comes to metabolic health,” says Jonathan Jun, M.D., associate professor of medicine at the Johns Hopkins University School of Medicine. “When people eat identical meals at two different times, their bodies apparently process those calories differently. How an individual responds depends on their particular biorhythms and sleep behaviors.”
Although we have this internal clock, the circadian rhythm can also be influenced by the external environment. The human body can adapt its own internal clock to the 24-hour period of daylight and night. This relates specifically to the circadian rhythm that controls our sleep-wake cycle. In fact, most people think of the circadian rhythm as the clock that controls when we sleep and when we are awake, but it is so much more, as we will learn.
Disruption of our circadian rhythm has been associated with decreased cognitive (thinking) performance, and increased risk of obesity, diabetes, and cancer. The body can no longer maintain its proper homeostasis (balance). Many of the hormones in the body have rhythms that fluctuate during daylight hours. Two of the most important hormones that are regulated by the circadian clock is cortisol and melatonin. Often it is our lifestyles which no longer are in tune to the patterns controlled by the circadian clock, that predispose us to metabolic disorders such as diabetes, and cancer. This is specifically seen in the increased incidence of illness in shift workers, who do not adhere to the normal body patterns of sleep/wake and food intake/fasting cycles.
Most organs and tissues in our body also contain biological clocks and are capable of functioning in a circadian fashion. Certain proteins in the body are “time-keepers”, and they interact with cells throughout the body, either telling them to be more active or to slow down. A scientific breakthrough in the 1970s discovered that we have a “master clock” in our brain called the “suprachiasmatic nucleus”, or SCN. The SCN is a tiny region of the brain, contained in the hypothalamus, controlling all the other biological clocks in the body, keeping everything in sync. It works autonomously and is self-sustaining.
The SCN is also partly controlled by the amount of light that comes through our eyes, and thus regulates a 24-hour rhythm throughout the body aligning its function with periods of daylight and darkness. Other input that the SCN receives from other parts of the brain also assist in its time-keeping functions. Thus, light not only controls our sleep-wake cycle, but many other functions of the body that adjust themselves throughout a 24-hour timespan. Any exposure to light can alter the circadian rhythm, known as a “phase shift”. For example, if you are exposed to light during the night, it will affect sleeping patterns and shift sleep to a later time.
Our body is designed to start to feel sleepy when the sun begins to go down, in response to the decreased amount of light that enters our eyes. When darkness falls, the optic nerve sends a signal to the SCN, which then signals the pineal gland in the brain to start producing melatonin. In terms of its 24-hour rhythm, elevated melatonin levels only happen during periods of darkness. Once melatonin is produced, it leaves the pineal gland, and travels throughout the body, preparing various systems of the body for sleep. Levels of melatonin during the night increases 10–20 times above the levels that are present during the day. Melatonin suppresses certain signals in the brain that keep us awake. It also lowers body temperature and produces a sedating effect, preparing the body for sleep. Melatonin levels peak at about 2–4 a.m., and then slowly drop off to prepare the body for wakefulness in the morning. Levels also change throughout the year, with higher melatonin levels in the fall and winter months, when the nights are longer, and lower levels in the spring and summer.
Artificial light during periods of darkness can interfere with melatonin production, and thus affects the body’s ability to sleep. The blue light from electronic devices mimic sunlight; many people have trouble sleeping if using electronic devices late into the evening. Traveling through multiple time zones, restricting sleep at night, or doing night shift work will result in a mismatch between the internal circadian rhythm of the body and the external light-dark cycle. When this occurs, symptoms include decreased alertness, motor coordination and cognitive performance, sleep disturbances, digestive system disruption and lack of appetite. Sleep restriction and daytime sleep are associated with an increased body mass index (BMI), risk of metabolic syndrome and alterations in insulin, sugar, and cortisol levels.
Taking melatonin supplements can induce sleep at times when the body clock does not normally trigger sleepiness, for example, in people who do night shift work and must sleep during the day, or when needing to reset the sleep-wake cycle when traveling through different time zones to prevent jet lag.
Cortisol is a hormone, which regulates many vital processes in the body, including metabolism in controlling blood sugar levels, influencing the formation of memories, controlling the salt and water balance, influencing blood pressure, acting as an anti-inflammatory, assisting with immune function and lowering sensitivity to pain; cortisol also helps the body respond to stress. Cortisol is
secreted by the adrenal gland, and it also has a circadian rhythm. Cortisol levels are lowest at night, and reach their peak in the morning when we wake up. The levels then drop during the day. In people who do night shift work, cortisol levels are reversed, thus cortisol is affected by one’s daily activity and sleep patterns. Cortisol boosts energy production when we wake up and when we exercise, to release glucose into the bloodstream, to be taken up by the muscles as a fuel source. It also suppresses insulin so that the glucose is not stored but is available for immediate use. It also releases fat from adipose tissue, reducing weight. Cortisol increases blood pressure, preparing us for activity. Thus, cortisol release is triggered by our sleep-wake circadian rhythm, it is in lower levels in the body when we least need it during sleep.
Studies show that melatonin decreases the production of cortisol from the adrenal glands. Thus, melatonin and cortisol, working together, appear to stabilize the circadian rhythm of multiple systems in the body. Shift workers doing night work and sleeping during the day had significantly lower levels of melatonin overall than those who worked during the day. Serum cortisol levels were also lower. Chronic reductions in melatonin and cortisol can have a cancer-causing effect.
In relation to digestion, a study was done with participants either eating a meal at 6 p.m. or 10 p.m. Those who had the later meal, had higher spikes in blood sugar (30% more), less breakdown of fat (by 20%) leading to increased fat absorption by the cells, and elevated levels of cortisol, which can lead to weight gain. This study proves that even when eating identical meals, the way the body processes calories is completely different depending on the time of day that the meal is eaten, indicating a circadian rhythm in the efficiency of the digestive process.
Also, extra cortisol is released by the adrenal gland in response to stress, to help the body respond appropriately. Cortisol is known as the “stress hormone.” It prepares the body for stress by raising heart rate and blood pressure, to ensure that the body can react with either “fight or flight”. However, if your body is under constant stress, the body continually pumps out cortisol. Ongoing high levels of cortisol can have a negative impact on your health, with impacts that counteract the function of normal cortisol levels, including impaired immune function, leading to more infections and increasing the risk of cancer and auto-immune diseases, increasing inflammation leading to heart attacks and strokes, elevation of blood sugar and blood pressure. Lack of sleep can affect the stress response, and increase the risk of metabolic and cognitive effects due to high cortisol levels. When stress levels are high in response to a threat, the body shuts down less important functions including the digestion of food.
Ghrelin, another hormone, is released by the stomach when it is empty, and is known as the “hunger hormone.” It travels through the bloodstream to the brain, and sends signals to increase appetite, thus stimulating food consumption. It also triggers fat absorption. Levels of ghrelin are highest just before a meal, and lowest just after a meal. However, studies have shown that when people eat during the period of time when the body normally rests, ghrelin production remains high instead of dropping off after a meal, which can trigger overeating. Overall ghrelin levels increased by 24% when eating at night. Shift workers who eat at night are at risk for developing weight gain and metabolic illnesses such as diabetes. Ghrelin is involved in the complex processes that maintain a healthy energy balance—energy input, by adjusting hunger signals—and energy output, by adjusting the amount of calories that goes into fat cells and glycogen (sugar) storage.
The body’s use of glucose also fluctuates with a circadian rhythm, controlled by the SCN, with the most efficient use of glucose by the liver occurring during normal pattern waking hours. Eating outside of these hours can raise blood sugar to unhealthy levels.
Insulin sensitivity is also reduced when eating at night, which can bring on a pre-diabetic state, with elevated blood sugar levels. It has been shown in studies, when shift workers change their eating patterns to align with normal activity times during daylight hours, blood sugar levels drop and weight gain is prevented.
Metabolism of fat also has a circadian rhythm, with disruptions in the circadian rhythm causing increased accumulation of triglycerides into fat cells, and elevated blood levels of cholesterol and fats.
Leptin is a hormone produced by the fat cells; when this hormone is released, it inhibits hunger, promotes satiety (feeling full), and also decreases the amount of fat that is taken up by adipose (fat) cells. When melatonin levels rise during the night, it also causes leptin levels to increase. This causes a decrease in appetite during sleep. However, sleep deprivation lowers leptin levels, thus increasing one’s appetite at night. When eating at night, leptin levels are 18% lower than they are during the day, thus the hormone’s ability to curb hunger is lessened, and typically more food is consumed than would be during the day; also the amount of fat intake into adipose cells increases. Thus, eating late at night can lead to diabetes and obesity. Also, in obesity, a decreased sensitivity to leptin occurs, leading to loss of the sense of satiety (feeling full) despite high levels of leptin in the body and high energy stores.
Not only do hormones fluctuate on a 24-hour basis, but sleep plays a vital role in regulating hormone levels. Lack of sleep itself can trigger increased levels of ghrelin and decreased levels of leptin, leading to increased hunger and appetite. This makes overeating more likely, as staying up late can also increase opportunities for food intake. Then, after a big meal, the body needs to use energy to digest the food, which can take several hours. However, digestion slows during sleep, which puts your normal time for sleeping at odds with the stomach’s need to digest food. Late eating has been shown to disrupt normal sleep for this reason. And the more calories that are consumed the worse the sleep becomes. Certain foods also impact sleep more, for example, meals low in fibre and high in sugar and saturated fats; this occurs by increasing body temperature, which goes against the body’s typical process of cooling down during sleep.
Disrupting the circadian clock by restricting the amount of sleep is also detrimental to one’s health. Studies done in children show that reduced sleep duration was associated with an increased risk of obesity 3–5 years later. These studies may explain increasing rates of obesity in children and teenagers. It has been proven that reduced sleep duration during adulthood (typically less than six hours) increases the risk of diabetes because of reduced insulin sensitivity, and increases in glucose, cortisol, and leptin.
Another interesting fact is that when eating at night, appetite for high carbohydrate foods increased by 43%, thus people consume more calories when sleep-deprived, due to increases in feelings of hunger from elevated levels of ghrelin, and decreased satiety from decreased levels of leptin. Insufficient sleep also affects parts of the brain that determine how we think of food, seeing it as a positive reward, also increasing the chance of eating too much. Persistent eating late at night can modify the amount and type of food eaten.
Circadian rhythms optimize our health, by coordinating many of the functions of the body. When we eat impacts the health of these daily biological rhythms. Erratic eating patterns can disrupt these rhythms, leading to chronic diseases that are so often part of the aging process. Just maintaining a strict feeding-fasting cycle, even without dramatic changes in the nutritional quality or quantity of food can reverse these chronic diseases. In studies, optimizing eating times, especially with prolonged overnight fasting is connected to protection against breast cancer. Therefore, being mindful to the body’s internal clock, and adhering to the optimal timing of sleeping and eating patterns can improve our overall health and prevent disease.
Let us close with a quote from Sister White: “Another pernicious habit is that of eating just before bedtime. The regular meals may have been taken; but because there is a sense of faintness, more food is taken. By indulgence this wrong practice becomes a habit and often so firmly fixed that it is thought impossible to sleep without food. As a result of eating late suppers, the digestive process is continued through the sleeping hours. But though the stomach works constantly, its work is not properly accomplished. The sleep is often disturbed with unpleasant dreams, and in the morning the person awakes unrefreshed and with little relish for breakfast. When we lie down to rest, the stomach should have its work all done, that it, as well as the other organs of the body, may enjoy rest. For persons of sedentary habits late suppers are particularly harmful. With them the disturbance created is often the beginning of disease that ends in death.” –Child Guidance, p. 389
Next month: we will continue to learn about the health impacts of timely eating
Helen Marttinen