How Your Body Clock Impacts Your Weight (and How to Reset It)
Your internal body clock affects your eating patterns, and when disrupted, it leads to binge eating and higher calorie consumption.
STORY AT-A-GLANCE
The circadian rhythm acts as the body's internal 24-hour timekeeper, regulated by the suprachiasmatic nucleus (SCN) in the brain, which coordinates sleep, hormones, metabolism and other bodily functions
When your body clock is disrupted, it leads to reduced insulin sensitivity and hormonal imbalances, including increased cortisol and decreased leptin, contributing significantly to weight gain and metabolic issues
Recent research revealed that liver “clock genes” communicate with the brain through the hepatic vagal afferent nerve (HVAN), influencing eating patterns and offering new therapeutic approaches
Modern lifestyle factors disrupting circadian rhythms include artificial blue light from electronic devices, shift work, irregular sleep schedules and social jetlag from inconsistent weekend sleep patterns
Resetting your internal clock requires consistent sleep schedules, morning sunlight exposure, limiting evening artificial light, regular meal timing and maintaining proper exercise routines during daylight hours
Ever feel like you’re doing everything right — eating healthy, hitting the gym — but the scale just won't budge? It can be incredibly frustrating. While diet and exercise are crucial for weight management, there’s another key player that often gets overlooked — your body’s internal clock, also known as your circadian rhythm.
The circadian rhythm acts as an internal timekeeper that regulates a wide range of bodily functions, and disruptions to it significantly impact your metabolism, hormones and even your behavior1 — all of which contribute to weight gain. Understanding this connection is essential for achieving your weight management goals and improving your overall health.
What Makes Us Tick — Decoding Your Body's 24-Hour Rhythm
Your circadian rhythm is a 24-hour cycle that governs many of your body’s processes. Like a conductor leading an orchestra and keeping all the musicians in sync, your circadian rhythm keeps all your bodily functions working together harmoniously.
This internal clock influences everything from when you feel tired and awake to when your body releases certain hormones. This cycle is found not only in humans, but also in most living things, including plants, animals, fungi and even some bacteria.2
At the heart of this system is a tiny region in your brain called the suprachiasmatic nucleus (SCN). This is often referred to as the “master clock” because it’s the main control center for your circadian rhythm. The SCN receives light cues directly from your eyes. When light enters your eyes, it sends signals to the SCN, which then interprets these signals to determine the time of day. This helps synchronize your internal clock with the external world.3
The circadian rhythm influences a vast array of bodily functions. The most obvious is the sleep-wake cycle, which determines when you feel tired and alert. It also plays a crucial role in hormone release, particularly melatonin (which promotes sleep) and cortisol (the stress hormone).
Body temperature, digestion and metabolism are also under the influence of this internal clock. A common example of circadian rhythm disruption is jet lag. When you travel across time zones, your internal clock is out of sync with the local time, leading to fatigue, difficulty sleeping and other symptoms.
It's important to recognize that everyone's internal clock is slightly different. This leads to the concept of chronotypes, which categorize people as either "morning larks" (who naturally wake up early and feel most energetic in the morning) or "night owls" (who prefer to stay up late and feel more productive in the evening). These individual differences in circadian rhythm significantly affect daily routines, preferences and even how well someone performs at certain times of day.
When Your Clock Is Off, Your Weight Goes Up
When your circadian rhythm is disrupted, it significantly impacts your metabolism, leading to reduced insulin sensitivity — this means your body doesn't respond as effectively to insulin, a hormone that regulates blood sugar, increasing your risk of developing Type 2 diabetes.4 It also affects how your body processes glucose (sugar) and how it burns fat for energy.
Think of your metabolism as a factory. If there's a power outage, the factory can't function efficiently, The same is true for your metabolism when your internal clock is off.
Circadian rhythm disruption also throws your hormones out of balance. It leads to increased levels of cortisol, the stress hormone. Elevated cortisol increases your appetite and promotes fat storage, especially around the abdomen.5
At the same time, it decreases levels of leptin, a hormone that signals fullness, making you more likely to overeat. The regulation of ghrelin, the hunger hormone, is also disrupted, further contributing to increased appetite.6 Shift workers, who often have irregular sleep schedules, are a prime example of how circadian disruption leads to weight gain and metabolic problems.7
Disruptions to your body’s natural rhythm also lead to behavioral changes that contribute to weight gain. People with disrupted circadian rhythms often find themselves eating late at night, often choosing unhealthy snacks. They may also experience decreased physical activity due to fatigue and poor sleep quality. Poor sleep also triggers cravings for high-calorie foods as your body seeks quick energy to compensate for the lack of rest.
Sleep deprivation, which is often a consequence of a disrupted body clock, further compounds the problem. When you don't get enough sleep, it exacerbates the hormonal imbalances already present due to circadian disruption, further promoting unhealthy eating habits and weight gain. Studies have consistently shown a link between insufficient sleep and increased risk of obesity.8 9
A New Piece of the Puzzle — Study Sheds Light on the Liver-Brain Connection
While the link between circadian rhythm disruption and weight gain is well established, the exact mechanisms behind this connection haven't been fully understood. However, a recent animal study published in the journal Science sheds new light on how the liver and brain communicate to regulate food intake patterns. This research offers exciting insights into the complex interplay between our internal clock, metabolic health and, ultimately, our weight.10
The study focused on the liver, which is responsible for various functions, including processing nutrients, detoxifying the body and regulating blood sugar levels. Interestingly, the researchers discovered that the liver also plays a crucial role in our internal clock. They found that the liver contains its own set of "clock genes" that regulate its daily activity cycles.
According to SciTechDaily, “Even though the SCN manages overall timing, nearly all cells in the body — including those in the liver — have their own internal clocks.”11 In mice, when these liver clock genes were disrupted, it led to a breakdown in communication between the liver and the brain.
The key communication pathway between these two organs is the hepatic vagal afferent nerve (HVAN), a nerve that acts as a messenger, sending signals from the liver to the brain's "feeding center," the arcuate nucleus. To simulate having a disrupted liver clock in the test subjects, the researchers targeted genes called REV-ERBs, which are important proteins in liver cells that help regulate the body's internal clock.
When their liver clocks were disrupted, the HVAN sent out faulty signals — this led to altered food intake patterns. The mice began consuming more calories during their resting phase and throughout the day, even when they weren't hungry.12
According to the study's senior author, Mitchell Lazar, MD, Ph.D., the director of Penn Medicine's Institute for Diabetes, Obesity, and Metabolism, and the Ware Professor of Diabetes and Metabolic Diseases:
“Both mice and humans normally eat at times when they are awake and alert, and this circuit provides feedback from the liver to the central clock in the brain that keeps the system running smoothly.”13
The good news is that the study also found a potential solution. When the researchers severed the HVAN in mice with disrupted liver clocks, it essentially blocked the transmission of the faulty signals. Remarkably, this intervention normalized the eating behavior in these mice.
“These findings open the door to future therapies that can target specific neural pathways to help those struggling with metabolic disorders caused by irregular eating schedules.
Future research should focus on what kind of chemical signals the liver sends to the vagus nerve, to help us understand how the liver affects the brain and the body through this communication,” Lauren N. Woodie, Ph.D., a post-doctoral researcher in Lazar's lab, said.14
Modern-Day Culprits Behind Circadian Rhythm Disruption
One of the biggest culprits disrupting our circadian rhythm today is artificial light, especially the blue light emitted from electronic devices like smartphones, tablets and computers. This blue light interferes with melatonin production, the hormone that makes you sleepy, making it harder to fall asleep and stay asleep. Using these devices right before bed significantly delays your sleep onset and disrupts your sleep quality.
Shift work and irregular work schedules are another major source of circadian disruption. Working nights or rotating shifts forces your body to operate on a schedule that’s out of sync with the natural day-night cycle. This leads to a host of health problems, including weight gain, metabolic disorders and even an increased risk of certain cancers.
Social jetlag, which is the difference between your weekday and weekend sleep schedules, also contributes to circadian disruption. Many people tend to sleep in on weekends to catch up on sleep they missed during the week. However, this shift in sleep timing throws off your internal clock, making it harder to get back on track when the workweek starts again. It’s like constantly changing time zones every weekend, making it difficult for your body to establish a consistent rhythm.15
Other factors, such as chronic stress, poor diet and lack of exposure to natural sunlight, also contribute to circadian rhythm disruption. These factors further amplify the negative effects on your health and weight.
Reset Your Rhythm and Reclaim Your Health — Practical Steps to Sync Your Body Clock
The good news is that there are ways to reset your internal clock and improve your circadian health. One of the most effective strategies is to prioritize light exposure. Getting plenty of natural sunlight in the morning helps regulate the SCN and promotes wakefulness during the day. Conversely, it’s important to minimize exposure to artificial light, especially blue light, in the evening. This helps your body produce melatonin naturally and prepare for sleep.
Establishing a regular sleep schedule is also crucial. Going to bed and waking up at the same time every day, even on weekends, helps reinforce your body’s natural rhythm. This consistency signals to your body when it’s time to sleep and when it’s time to be awake.
Diet and exercise also play important roles. Eating healthy, regular meals at consistent times helps regulate your metabolism and hormone levels, while avoiding late-night snacks prevents your digestive system from working overtime while you sleep. Exercising regularly, preferably during daylight hours, also helps regulate your circadian rhythm and improves sleep quality.
Creating a relaxing bedtime routine, such as taking a warm bath, meditating or reading a book, will help prepare your mind and body for sleep. Optimizing your sleep environment by ensuring it’s dark, quiet, and cool also boosts sleep quality to enhance your circadian health. For more helpful tips to improve your sleep, read “Top 33 Tips to Optimize Your Sleep Routine.”
Syncing Your Internal Clock for a Healthier You
The connection between your circadian rhythm and your weight is undeniable. Disruptions to this internal clock will have a profound impact on your metabolism, hormones and behavior, ultimately leading to weight gain. By prioritizing your circadian health, you can take control of your weight management efforts and improve your overall well-being.
Implementing the practical strategies discussed — avoiding artificial light at night, getting bright morning sunlight, establishing a regular sleep schedule, prioritizing healthy diet and regular exercise, and creating a conducive sleep environment — will help you reset your rhythm and reclaim your health. Taking these steps is an investment in your long-term health and well-being, paving the way for a healthier, happier you.
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