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  • Biological clocks, circadian rhythm and weight control

    Many associate weight gain with eating high fat, high calorie food, and a lack of exercise. Recent advances in medicine discovered that there is another important factor, possibly more important than the type of food you eat, which could affect the body's weight. That is our own biological clock. Most of us know that the "biological clock" is important in regulating the daily functions of our bodies, what we don't realize, is just how important this clock really is; and the fact that the "biological clock" is actually an intricate network of "clocks", which are made up by a group of molecules that is present in nearly all cells throughout our bodies. This means almost every single cell in our body has its own clock. All these clocks are controlled, synchronised and coordinated by a master clock in the hypothalamus of the brain called suprachiasmatic nucleus pacemaker neurons. The biological clock influences almost all physiology and behavior in humans, such as sleep-wake cycles, cardiovascular activities, endocrine system that controls the body's metabolisms and hormone levels, kidney activities, and gastrointestinal and liver functions. In addition, the biological clock has been linked directly to lipid (fat) metabolism (Froy 2010, Endocrine Reviews). The disruption/alteration of these clocks will have implications on the gastrointestinal and metabolic functions of the body and consequently influence our food digestion, processing and absorption that are essential for maintaining a healthy body weight and personal well-being.

    The regulation of our master clock is based on the 24-hour light and dark cycle where our earth rotates along its axis. As such, the principle signal for the regulation of our master clock is light, which then sends output signals to the clocks in other cells of the rest of the body to synchronize their functions. This system allows the body to produce optimal functions at optimal times within a 24-hour day. However, unlike the master clock in the brain, the individual clocks in our tissues can also be affected and reset by stimuli other than light, such as eating times. As a result, this can create time "misalignment" between individual clocks in our body and the mater clock in the brain.

    Circadian rhythm is the daily physiological and behavior patterns driven by our biological clocks. Part of its functions is metabolizing food and nutrients and managing energy input and expenditure, hence maintaining optimal body weight. This rhythm can be disrupted by our own voluntary behaviors, such as irregular eating habits or working irregular shifts, outside the control of the master clock in our brain. When time misalignment occurs between different parts of the body, the balance of the body's energetics and metabolism will be disturbed, and potentially serious health related issues would follow, including obesity and diabetes (Wong et al. 2007, PNAS; Scott et al, 2008, International Journal of Obesity), which in turn will affect circadian rhythm, creating a vicious circle.

    Ok, until now I have emphasized enough about the importance of our biological clocks and circadian rhythm in maintaining a healthy body weight, and probably scared enough people about the potential metabolic and weight management complications associated with the disruption of this rhythm. The reality is, we live in a highly stressful and demanding society, it is almost impossible for an average Joe like you and me, to plan our lives based on our innate rhythms and clocks. We need to work with other people's schedules, we have responsibilities on our shoulders and deadlines to meet, all at the expense of our circadian rhythm. But remember, at the end of the day, we neglected one thing that is the most precious to us, our own health. Although it is unrealistic to plan our daily lives fully based on our own exact circadian rhythms, partly because even with all the advanced medical technologies at hand, we are still not sure what the precise rhythm for each organ is, we could follow some general principles, which would put us more or less on the ball park.

    Evidence has indicated that there is a direct link between the fluctuation of the body temperature of a mammal throughout a day (yes, the body temperature of warm blooded mammals fluctuates) and circadian rhythm (Buhr et al. 2012, Science). By looking at a graph of an average person's body temperature cycle, it is not hard to figure our how we should plan our daily activities. The body temperature is an indication of metabolic rate, and it is at the lowest at around 6am each day and gradually increases as the day goes on. There is a little dip in temperature at around 1pm, which is why many of us feel tired and sleepy at around that time. Body temperature reaches its highest level at around 6pm and then it's all downhill from there, until reaching the lowest point at 6am, the cycle is complete.

    circadian-rhythmResults from numerous studies unanimously concluded that the time one eats and the time one sleeps are two important daily rituals that help to manage body weight and BMI, more so than the amount of calories contained in the food. Our body functions according to the 24-hour light-dark cycle. At light we eat; at dark we sleep.

    Since we first came to existence, our body is designed to fast overnight and only eat during the day. This practice follows our natural circadian rhythm and allows our organs and tissues to properly rest and recover from a day's activities. However, we now live a very different lifestyle compared to what we are evolved as humans to live. This disrupts the metabolic pathways controlled by our natural circadian rhythm, and some speculate that it is one of the main causes of the current obesity epidemic in many first world countries.

    It has been shown that eating at night is less satisfying than eating in the morning, which results in over-eating (de Castro, 2004, Journal of Nutrition). Nighttime eating can result in higher fatty acid uptake and triglyceride storage in scientific studies conducted in animals (Bray and Young, 2007, Obesity Review). A more recent study also found that mice eating during a restricted 8-hour period are significantly leaner and healthier than those consumed the same amount of calories but were allowed to eat freely throughout the day, regardless of the content and quality of the diet (Hatori et al. 2012, Cell Metabolism). This suggests that having a high fat diet is not the main culprit for weight gain. The time which people eat their meals can have a bigger impact on body weight and metabolic functions. If the Hatori study is applicable in humans, by consuming food frequently only during the 8 hour day period and fast at night, we will cure obesity, regardless of what type of food we eat. How about that?

    Another important aspect of maintaining correct circadian rhythm is sleep. Sleep depreciation, short sleep and poor sleep quality have been associated with diabetes, higher BMI, metabolic syndrome, increased appetite and obesity (Huang et al. 2011, Journal of Clinical Investigations). People who habitually sleep less than 6 hours or over 9 hours per night have an in crease risk of developing type 2 diabetes and impaired glucose tolerance (Gottlieb et al. 2005, Archives of Internal Medicine). The duration of wakefulness at times when one should be sleeping is directly related to BMI and waist to hip ratio independent of age, sex and physical activity (van Amelscoort et al. 1999, International Journal of Obesity Related Metabolic Disorders). So if you want to be lean, make sure to sleep 7-8 hours a day, can't be that hard!

    It is true that many of the studies mentioned above were conducted using animals not humans. However, the biological clock is present in all living things on earth, even in plants. Its function to regulate the body's physiology and behavior based on the 24-hour earth cycle is shared across species. Therefore, it is reasonable to assume that findings from animal studies can be translated into humans, possibly with small variations of course.

    Even though living a balanced life based on the biological clock and circadian rhythm has been described in alternative medicine for centuries, it is still a relatively new field in modern western medicine and science. Modern technologies however, provided concrete scientific evidence linking the biological clock with the well-being of the body as well as obesity. Thus by adapting eating/sleeping habit with this rhythm, one can maximize the body's potential, and subsequently improves its well-being.

    An adaptation of the appropriate eating/sleeping pattern for obtaining the ultimate lean body based on the circadian rhythm should look something simple like this: eat regularly during the day, have more food in the morning and gradually decrease the amount as the day goes by; try not to eat at night if you can help it and make sure to get 7-8 hours of sleep per night. Sounds simple, right? Of course, each person is different. This is just a basic framework that can be modified based on one's own personal circumstances. The important thing is that you know the science behind it.

    Researching and writing this article made me realize just how in-one we are with our surrounding environments, the earth and even the universe. We function by the basic rules of nature, regardless of how superior we think we are compare to other organisms on earth. We all want to be healthy and feel good about ourselves. We pursue that by taking the best supplements, go through the tedious exercise regimes, eat some of the most ridiculous foods. They do work, however, we forgot the most basic and important factor, the rhythm of ourselves. Play by rule of nature and you will live a healthy and feel-good life.

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