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What to eat and how much to eat have significant health consequences. But what about the timing of a meal – does when a person eats have health implications?
There are some examples of this timing consideration in traditional medicine practices. Meal timing is a key piece of the health puzzle in Ayurveda, an ancient healing system that originated in India. In Ayurveda, it is believed that physiological processes are aligned with the natural cycles of the day; therefore, there are timing guidelines for food intake, physical activity, and sleep. Similarly, Traditional Chinese Medicine (TCM) believes each organ possesses its own rhythm. Following this practice, certain therapies are recommended at specific times of the day. Both alternative healing modalities encourage individuals to live in sync with daily cycles to foster health.
The circadian rhythm
Current scientific research is validating ancient wisdom. Research on the circadian rhythm is shedding light on the metaphor of the “ticking biological clock.” The 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 the circadian rhythm or the series of physiological and behavioral changes that occur throughout a 24-hour 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.
Several physiological reactions are intertwined with our circadian rhythm, including our sleep and wake cycle, body temperature regulation, hormone fluctuations, food intake, and detoxification processes. Research suggests that synchronizing the administration of drugs for certain conditions (such as asthma, cardiovascular disorders, rheumatoid arthritis, and several types of cancer) with circadian rhythms appears to be of considerable importance in increasing success rates and decreasing side effects. Major influencers of the circadian rhythm are light/dark, temperature, fasting/eating, and rest/activity. Mutations to the “clock genes” or any changes to the body’s natural rhythm can disturb its delicate balance and open the door to disease.
Studies conducted on both animal and human subjects have shown that a disruption in the circadian rhythm is associated with metabolic syndrome, obesity, type 2 diabetes mellitus, cardiovascular disease, gastrointestinal diseases, mental disorders, and cancer risk. One study found that disruptions to the normal circadian rhythm caused altered hormone secretions and insulin resistance. Researchers found that metabolic abnormalities were improved through time-restricted eating, which restored gut hormone secretions and activated brown fat thermogenesis.
Disruptions in the sleep-wake cycle appear to increase the risk of developing metabolic diseases. A cross-sectional study on 200 night shift workers assessed the connection between night shift work and obesity. Researchers found that night shift workers, compared to day shift workers, were more obese, independent of age or gender. Night shift workers also slept fewer hours and had increased levels of social jetlag, which is associated with obesity and defined as a discrepancy in sleep patterns between workdays and weekends when more social activities tend to occur. However, a systematic review of 15 randomized controlled trials found that disruptions to sleep/wake cycles, as is common in night shift workers, may also be amplified by other risk factors, including unhealthy diets, inactivity, and meal-skipping.
How meal timing and composition affect health
Meal timing and the composition of meals appear to affect metabolic function. When mealtimes fall outside of the body’s circadian rhythm, the master clock and peripheral clocks are out of balance. This desynchrony is associated with glucose dysregulation, reduced insulin sensitivity, increased blood pressure, increased levels of inflammation, increased calorie consumption, and reduced energy expenditure. Studies have shown that eating meals later in the day may cause an increased risk of developing metabolic diseases, including obesity and diabetes. Additionally, late-night eaters may experience heightened appetites due to increased ghrelin and decreased leptin, which can further increase the risk of developing metabolic diseases.
Late-night eating may lead to poor sleep quality. A recent randomized crossover trial conducted on 10 men and 10 women found that eating a meal an hour before bedtime caused glucose intolerance and reduced fatty acid oxidation. During sleep, the metabolic rate decreases, and nutrient metabolism shifts toward fatty acids. However, if eating late at night causes elevated glucose and lower fatty acid oxidation, individuals are at risk of increased adiposity and body weight. Another concern is that digestion patterns slow at night, which means late-night eating may cause discomfort, acid reflux, and heartburn. Researchers also concluded that late-night eating led to a heightened glucose and insulin response after breakfast the next day, which further increases the risk of developing a metabolic disease if this eating pattern becomes chronic.
An extreme example of the effects of late-night eating can be seen in individuals who experience night eating syndrome (NES). NES is characterized by excessive food intake at night. It is associated with increased body weight, obesity, poor sleep, and depression. Because circadian rhythm is altered by meal timing, and sleep insufficiency affects hunger, appetite, and the reward center of the brain, NES is correlated with the development of metabolic disease.
Other human studies have shown that alterations in meal timing, or meal irregularity, may contribute to the risk of metabolic diseases. A randomized crossover trial on 30 persons who were overweight or obese compared morning-loaded versus evening-loaded weight loss diets. While both diets resulted in similar weight loss, morning-loaded diets contributed to less hunger. Ultimately, researchers found that the behavior of morning-loaded calories may help with weight loss compliance and suppression of appetite.
Unusual routines around eating times (i.e., erratic eating patterns) may be more disruptive to circadian rhythms. A study from 2017 evaluated 10 healthy men to see if mealtime alterations affected circadian rhythm. Over the 13-day study period, researchers found that constant routines did not affect the master clock markers melatonin and cortisol. However, late-night eating delayed plasma glucose and adipose PER2 clock gene expression. This means that meal timing may play a role in peripheral circadian rhythm synchronization and could be used to reset circadian rhythm disorders, along with night shift work and jet lag.
In addition to the timing of meals, meal composition and dietary patterns may influence the circadian rhythm. For example, a high-fat diet disrupts the circadian rhythm and causes a reduced amplitude (i.e., a weak rhythm). This diet changes circadian gene expression and increases inflammation. In animal models, high-protein diets were also found to negatively influence the circadian rhythm by affecting liver lipid metabolism. Both protein and carbohydrates are associated with changing the expression of clock genes. PER2 and Rev-erbα are expressed with these foods but are normally at peak expression during daytime hours.
A study from 2007 compared the effects of a high-glycemic and low-glycemic meal in the 4 and 1-hour windows before bedtime. They revealed that the high-glycemic meal consumed 1 hour before bedtime increased sleep onset latency, thereby prolonging the time it took to fall asleep. However, consuming that same meal 4 hours before bedtime reduced sleep onset latency. This suggests that meal composition and timing are important considerations, but more studies are needed to confirm this finding and elucidate the effects of other dietary patterns on health and sleep.
Based on the current body of evidence, it seems that meal timing and composition do play a critical role in determining health outcomes, and it can potentially be used as a measure to forestall obesity and other metabolic diseases.
What is chrononutrition?
Chrononutrition refers to coordinating food intake with the body’s daily rhythms. Because a variety of enzymes involved in lipid and glucose metabolism are regulated according to circadian rhythms, chrononutrition may be a healthful approach. Disruptions to the circadian rhythm, such as nocturnal shift work or jet lag, may throw the body’s rhythm out of balance and increase the risk of disease.
For example, 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 cardiovascular problems, mood disorders, hypertension, diabetes, certain cancers, and obesity. However, establishing routines around sleep-wake cycles and eating times may partially restore circadian rhythm, and these risk factors improve. It shows the body’s resilience in its quest for balance.
A randomized crossover, 8-week study on 12 individuals found that an early eating schedule, compared to a delayed eating schedule, led to better weight loss outcomes, increased energy metabolism, and improved insulin sensitivity. Another study found that adopting a routine around eating an earlier breakfast (instead of prolonging or skipping) and earlier dinner (e.g., 8 PM vs. 9 PM) is beneficial for the prevention of cardiometabolic disease. Research suggests stopping food consumption before the 3-hour window before bedtime to improve sleep quality. It appears that time-restricted eating, in alignment with the circadian rhythm, may be beneficial to health.
Understanding an individual’s chronotype may be a further area of study. A longitudinal cohort study assessed 196 adolescents and how eating in alignment with their chronotype affected body composition. Each participant’s chronotype, or personal preference in the sleep/wake cycle, was determined to best align their timing of highest energy consumption. Participants with a later chronotype were found to have better body composition outcomes (i.e., increased fat-free mass) when aligning their calorie consumption with chronotype. This means that the presumed negative health outcomes from late-night eating may require further exploration of individual chronotypes to understand the metabolic effects.
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 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. While social media is a growing point of dissemination of information about chrono-nutrition, it is important to remember that the simplest practices—like eating meals at the appropriate times, getting bright light exposure during the day, and going to bed at a reasonable time—are sometimes the most powerful medicine.
If you have trouble sleeping, wonder if your chrononutrition is misaligned, or experience health complications, talk to your doctor, nutritionist, dietician, or another member of your healthcare team for personal options based on your individual circumstances.
