Tell me your daily routine, and I’ll tell you how healthy you feel. Tell me when you eat, and I’ll tell you if it is easy or difficult for you to maintain your weight. Tell me when you exercise, and I’ll tell you whether you are building your body’s systems or wearing them down. Tell me when you turn off your television or computer at night, and I’ll tell you how sensitive you are to stress. Tell me when you fall asleep, and I’ll tell you whether you need coffee to power your way through the afternoon, or whether you snap at your loved ones at the end of a long day when you wanted to be patient.
Does this sound like magic? It’s not. A growing body of science reveals how closely our bodies are linked to the circadian rhythm of light and darkness, right down to the cellular level. This research shows that when you eat is as important as what you eat, when you fall asleep is as important as how much sleep you get, and when you exercise is as important as how much exercise you get. Your daily schedule determines your weight, your stamina, your general health, and your mood. Don’t believe me? For decades, diabetes researchers have known that a simple way to trigger obesity in laboratory mice is to wake them up and feed them during their sleep cycle. In fact, mice gain weight within a week if researchers just expose them to low-level lights when they should be sleeping.
Still don’t believe me? Think back to the last time you experienced jet lag. How did you feel? Anyone who has experienced jet lag knows the symptoms can go far beyond sleep disruption. Often, you suffer from constipation, upset stomach, cognitive fog, low energy, and an increased sensitivity to stress. A recent study even linked jet lag to weight gain because disrupting your schedule through long-distance travel confuses the microbes in your gut.
Yet these same complaints—weight gain, insomnia, exhaustion, stress, depression—are the very things that bring people to my clinic. And, if you’re reading this book, I’d guess that these complaints sound awfully familiar to you, too. Thanks to the demands of modern jobs and 24/7 connectivity, many of us live in a constant state of self-imposed jet lag, sleeping, eating, and exercising at times that don’t coincide with the body’s natural rhythms. But there is good news, and I’m here to tell you what I tell all my patients: It’s not you; it’s your schedule. There is an easier way to lose weight, get energized, and get to sleep at night. By working with your body’s natural rhythms and not against them, you can create a daily schedule that will transform your health and your life.
The Circadian Rhythm
Physiologists know that the body has a natural rhythm—called a circadian rhythm—that operates on a nearly twenty-four-hour cycle, resetting itself every morning when you first experience daylight. This rhythm directs the body on when to digest food, how to prepare for sleep, and how to regulate everything in your body-including blood pressure, metabolism, hormone production, body temperature, and cellular repair. Your skin cells, too, repair and regenerate on a daily schedule. Even the population of microbes in your intestinal tract changes profoundly throughout the course of a single day. Certain strains of gut bacteria proliferate during the day, while others predominate at night. At every hour of the day, your body is changing its function. The cells and systems are primed to do different things, depending on the time of day or night. That’s how we know that you hit your deepest sleep cycle at about two a.m., that your body temperature is lowest at about four a.m. Your body’s sharpest rise in blood pressure comes at about six forty-five a.m., and a bowel movement is most likely at eight thirty in the morning. By ten in the morning, your mental alertness peaks, and your digestion is operating most efficiently at noon. Your coordination, reaction time, and cardiovascular strength peak in the afternoon while your digestion powers down. After sunset, your blood pressure hits its highest daily level, along with your body’s temperature. At about nine p.m., your brain starts releasing melatonin, and your digestion slows to half speed. By ten thirty, your bowel movements are suppressed, and your digestion is at a crawl. This happens, or should happen, every day. This is why your body gets so confused when you cross time zones. The light changes and the body loses its compass for controlling these bodily functions.
This is fascinating because we think we are so isolated from nature. We live in climate-controlled homes and work in offices or cubicles. And yet every system in our bodies is changing in a predictable, daily pattern. Your body is always trying to coordinate all of its systems on a central clock using available natural light. Every organism in nature operates in this cyclical way, and a new field within biology, called chronobiology, studies all the ways in which different organisms operate in accordance with a circadian rhythm.
What researchers are studying now is how our daily habits interact with this circadian rhythm, and they’ve discovered that the modern schedule profoundly disrupts it. Staying up late at night watching TV or doing work fools your body into thinking that night hasn’t started yet. Eating a big meal in the evening does the same thing. It delays the cycle and disrupts sleep, only to have you jolt the body awake first thing in the morning when your alarm goes off. Lack of exercise and natural light further disrupt the circadian rhythm, which in turn disrupts everything from your digestion to your hormone secretion and your nervous system.
Many of my patients routinely stay up until midnight, working and snacking, and then wonder why they can’t fall asleep until one. Then they drag themselves out of bed at six a.m. and wonder why they can’t eat or concentrate in the morning. A couple of hours of deviation from your body’s natural rhythm may not seem like much, but to put this in perspective: if you only sleep between one and six a.m., it’s as though you flew from California to New York in the evening, only to fly back before work. No wonder you feel sick.
Many of our most common physical complaints are created or exacerbated by a modern schedule at odds with the body’s needs. Fortunately, physiologists have generated a lot of new research about the body’s clock and how behavior either helps strengthen the clock’s signals or gets in its way. This new field is called chronobiology, and it offers insights about how you can set a daily schedule that will keep you healthy and energized.
How Your Body Tells Time
Your body always knows what time it is, even if you don’t. It may sound absurd to think that you don’t know what time it is. You are probably hyperaware of the time at every moment of the day. You have a train to catch or you have kids to drop off at school. You have a meeting in fifteen minutes and a call in an hour. You have to get to the dry cleaner before it closes. You have project deadlines, dinner reservations, and an alarm clock (or two) that wakes you every morning. My patients tell me that they are constantly aware of the time and that the clock dictates nearly every one of their daily activities.
But there is a different kind of clock inside your body, one that rules all of its cells and systems. To understand how it works, you have to step inside the brain and into the hypothalamus. The hypothalamus sits at the center of the brain and is responsible for regulating all of the body’s systems. It activates the fight-or-flight response when you feel stress or danger. It tells you when you are hungry or thirsty. When you begin a strict diet, the hypothalamus is what’s telling you that you are starving because you are eating differently. You may know that you aren’t starving, but the body is signalling to the brain that it’s not getting the same amount of food as before. When you start a new exercise routine, the body signals muscle fatigue and cardiovascular stress to the brain and the hypothalamus urges you to stop. And when you stay up late to work on a project, the hypothalamus is what’s telling you that you are sleepy and bored. So this part of the brain can read the body’s signals and try to affect your behavior, trying to keep everything the same as it was yesterday.
The hypothalamus also regulates all kinds of things that you don’t consciously control, including body temperature, hormone balance, and metabolism. All of these changes happen at predictable times of the day. For example, your body temperature peaks in the evening, then decreases during the night and reaches its lowest point just before dawn. Your blood pressure rises sharply as you wake up each morning, and then increases slowly throughout the day before falling during the night. The sharp rise of blood pressure in the morning comes at a time when blood platelets are stickiest, which explains why many heart-attacks happen first thing in the morning. Cortisol levels, too, change at predictable times. Cortisol is a steroid that the body produces and it’s sometimes called the ‘stress hormone’. The level of cortisol in your body is lowest when you go to bed and then accumulates during the night. It is partially responsible for your body’s inflammatory response, so it’s no wonder that those aches and pains are at their worst when you get out of bed, or that you feel most bloated and puffy in the morning. Cortisol levels discharge steadily throughout the day, fluttering briefly upward after every meal.
Colonic motility—which is a fancy term for bowel movements—changes during the day as well. First thing in the morning, the colon wakes and moves at three times its normal level of activity, with predictable results. That’s why so many people feel constipated while in the throes of jet lag. A poor eating schedule can also confuse the colon. At night, the colon rests and bowel movements are suppressed. Mood and brain waves alter throughout the day and night as well.
In order to regulate the body’s systems, your hypothalamus takes its cues both from the body’s tissues and organs and from the environment. When you smell food, you feel hungry; when you see danger, you feel anxious and energized for action. All true. But let’s don’t forget the most pervasive signal the brain takes in all day—the presence of light. There is a small part of the hypothalamus, called the suprachiasmatic nucleus (SCN) that is tasked with noticing light. It’s about the size of a grain of rice, and it contains approximately twenty thousand neurons. Physiologists have long understood that these neurons respond to light and regulate the body’s systems based on light and darkness. When light hits the retina of the eye first thing in the morning, the SCN signals to the body that it’s daytime. In the evening, the SCN helps signal the body’s natural production of melatonin that tells you when it’s time for sleep. But it’s only in the past twenty years that researchers have looked at how much power this tiny bundle of neurons exerts over every cell and system in the body.
Excerpted with permission from Change Your Schedule, Change Your Life by Suhas G. Kshirsagar. Now available in bookstores.