We know that what we eat and how much we eat has significant health consequences. But what about the timing of the meal? Could it also have health implications? Ayurveda, an ancient healing system originated in India, emphasizes meal timing as another key piece to the health puzzle. In Ayurveda, it is believed that our physiological processes are aligned with the natural cycles of the day; therefore, there are timing guidelines for food intake, physical activity, and sleep (1, 2). Similarly, Traditional Chinese Medicine believes each organ possesses its own rhythm, thereby recommending certain therapies at specific times of the day (3). Both of these alternative healing modalities encourage us to live in sync with these cycles in order to foster health. Now, emerging Western research seems to validate this ancient wisdom. Circadian rhythm research sheds new light into - and gives new meaning to - the metaphor of the “ticking biological clock”.
Our master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus receives input from the environment and synchronizes its rhythms to the outside world. This biological clock is the mastermind of our circadian rhythm or the series of physiological and behavioral changes that occur throughout a 24 h cycle. This master clock is also in sync with peripheral clocks located in other tissues such as the liver, adipose tissues, muscle, heart, stomach and lungs (4, 5).
Several physiological reactions are intertwined with our circadian rhythm, including our sleep and wake cycle, regulation of body temperature, hormone fluctuations, food intake and detoxification processes (4, 5). In fact, there is even research suggesting that synchronizing the administration of drugs for certain conditions (such as asthma, cardiovascular disorders, rheumatoid arthritis and several types of cancer) with our circadian rhythms appears to be of considerable importance to increase success rates and decrease side-effects (5). One of the major influencers of circadian rhythm is the light/dark cycle, followed by temperature, fasting/eating and rest/activity. As expected, any mutation to the “clock genes” or any changes to the body’s natural rhythm can disturb its delicate balance and open the door to disease (4).
Studies conducted in both animal and human subjects have shown that a disruption in circadian rhythm is associated with metabolic syndrome (6), obesity (7), cardiovascular disease (8) and cancer (9). One study conducted with 85 overweight and obese women found that circadian rhythm abnormalities, as measured by wrist temperature, correlated with decreased weight loss (10). The study concluded that an altered circadian rhythm could be in fact used as predictor of future weight loss. Furthermore, a rodent study showed that sleep restriction induced metabolic changes resulting in increased food intake and fat storage, contributing to obesity (11).
Similarly, other human studies have shown that alterations in meal timing increase the risk of metabolic diseases. For instance, a clinical trial (12) with 420 individuals in a 20-week weight loss program showed that despite consuming the same amount of calories, late eaters lost less weight than early eaters and also had higher insulin levels (which is related to blood sugar imbalances). In a different study (13) comparing two groups of overweight and obese women receiving the same amount of calories, it was found that the group given a bigger breakfast and a smaller dinner had greater weight loss and reduced waist circumference as well as improved metabolism. Another study (14) found that late eaters burned fewer calories throughout the day, had altered glucose tolerance, cortisol (stress) levels and wrist temperature leading to less circadian signaling to peripheral clocks.
So it seems that meal timing does play a critical role in determining health outcomes and it can potentially be used as a measure to forestall obesity and other metabolic diseases. In fact, the new term ‘chrono-nutrition’ (15) refers to coordinating food intake with the body’s daily rhythms. This appears to be a sensible approach - and one that is increasingly gaining attention as more research emerges - considering that a variety of enzymes involved in lipid and glucose metabolism are regulated according to circadian cycles. As such, any disruption to this rhythm as it happens with nocturnal shift work or jet lag (16) can throw the body’s rhythm out of balance and increase the risk of disease.
For instance, night shift-workers who veer from the normal physiological tendencies of the body (i.e., sleeping at night and being active during the day or eating at physiologically unsuitable times) have an increased risk of high blood pressure, high cholesterol, high triglycerides, atherosclerosis and heart attack (17). However, once the circadian rhythm is restored, even if only partially, these risk factors tend to improve (18). It goes to show the body’s resilience in its quest for balance.
Circadian rhythm is such a fascinating field of research because it validates the body’s wisdom and, in doing so, allows us to work with its natural rhythm in order to maintain or restore health. And instead of adding another layer to the pile of things we need to do to be healthy, it brings it back to basics. It serves as a reminder that the simplest practices - like eating meals at the appropriate times, getting bright light exposure during the day and going to bed early - are sometimes the most powerful medicine.
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