The Latest on the Sleep-Weight Connection and How Sleep Affects Gut Health

I know a lot of you are interested in the connection between sleep and weight. Me too! (In fact, I wrote a best-selling book about it.) I’m also deeply interested in the relationship between sleep and gut health. As we’re learning, the gut microbiome—the collection of trillions of microorganisms in our intestines—has a powerful influence over sleep, as well as other fundamental aspects of physiology, including digestion, mood, cognition, immunity, and hormone production. In turn, sleep can affect the health of the gut microbiome, and all those physiological processes it touches.

Science is continually uncovering new facets of the sleep-weight connection. And the emerging science on the role of the microbiome in sleep and health is deepening our understanding of just how important gut health is to how we sleep, think, and feel.

A couple of recent scientific discoveries on these topics are worth digging into for a closer look. They both involve what is probably the single most important sleep habit you can adopt: a consistent sleep-wake routine.

Your Weight Loss

Can the consistency of your sleep routine help you lose more weight? YES! 

Just about everyone who’s tried to lose weight has struggled at some point with a weight-loss plateau. You’re working hard to eat right and exercise, but the weight has stopped coming off. New research shows that getting enough sleep and sticking to a regular sleep routine can help you break through a weight-loss plateau.

Regular readers have heard me preach the importance of consistency in sleep schedules. Sticking to regular bedtimes and wake times—on weekdays and weekends, both—has a fundamental impact on sleep quality, helps you fall asleep more quickly and sleep more soundly, and helps to ensure you get the amount of sleep you need to perform at your best. Consistent sleep routines strengthen and reinforce circadian rhythms—and healthy bio rhythms come back to further improve the quality and quantity of sleep, along with protecting a healthy metabolism, sharper cognitive function, and a stronger immune system. (There’s very little about our minds and bodies that bio rhythms don’t influence.)

This new research shows how consistent sleep routines may help you kickstart a stalled-out weight loss goal. A study published recently in the International Journal of Obesity investigated how both sleep amounts and the degree of variability in sleep schedules affect weight.

Scientists tracked sleep, weight, and measurements of body fat (including waist circumference and BMI) in a group of more than 1900 overweight and obese adults, for a period of 12 months.

The takeaway?

  • Better Sleep will help your weight loss plateau
  • People who stuck to a more routine sleep schedule, with less variability in bedtimes and wake times, lost more weight than people whose schedules were less regular. The more consistent sleepers also saw greater positive changes to BMI, or body mass index.
  • Sleep amounts also mattered to weight loss. People who slept 7-9 hours a night lost more weight than people who slept less than 6 hours. The 7-9 hour-a-night sleepers also experienced greater reductions in waist circumference, an important indicator of abdominal fat. Too much abdominal fat is accompanied by greater risk for cardiovascular and metabolic disease.

Getting enough sleep AND sleeping on the same schedule are both critical for weight loss, weight management, and metabolic health. As much as we might wish it so, sleep isn’t something that can be shifted around, or set aside temporarily and made up for later, without having negative effects on our waistlines and underlying health. 

Other recent, related sleep-weight news:

A study conducted by scientists in Japan investigated how the time that elapses between eating dinner and going to bedmight affect blood sugar and metabolic health. What they found was that sleep was the significant factor, more so than the amount of time between an evening meal and bedtime. Scientists found that both short sleep and more variable (i.e., less regular) sleep routines were closely linked to obesity and to elevated blood sugar, a key factor in prediabetes and diabetes.

Scientists from the University of Colorado found that weekend catch-up sleep does not protect against the negative metabolic and weight-related effects of short sleep during the week. This study found people who didn’t get enough sleep during the work week, and who slept extra on the weekends to “catch up,” consumed more calories after dinner, expended less energy (aka fewer calories), and gained weight. Their bodies also used insulin less efficiently.

Your Microbiome

Irregular sleep schedules can disrupt a healthy gut 

I’ve been paying close attention to the emerging research on the relationship between sleep and the human microbiome. We’ve known for a while that a dynamic, complex two-way street exists between healthy sleep and a healthy gut, and that both are important to overall physical, mental, and emotional health.

Just-published research in the journal Nature has delivered some insightful new information about the connections between sleep, circadian bio rhythms, and the gut microbiome. This research points to a regular sleep routine as one way to protect and promote optimal gut and immune system functioning.

Before I jump into what we’ve learned, let’s do a quick refresher on what the microbiome is and why it matters so much:

  • The human microbiome is home to a nervous system and about 100 million neurons. For that reason, it’s often called the “second brain.” The microbiotic nervous system communicates constantly with brain and central nervous system, regulating hormone production, immune system function, appetite, digestion and metabolism, mood and stress responses. Every individual’s microbiome is unique in composition. Our microbiome develops as a result of genetic factors, along with the microbial life in our environments and diets.
  • The gut is a major producer of melatonin, a hormone essential for initiating sleep and maintaining sleep-wake cycles. The gut microbiome makes and releases other hormones that are critical to sleep, including dopamine, serotonin, and GABA among them.
  • The precise make-up of our individual microbiome is highly both dynamic and unique to each of us. There are tens of trillions of micro-organisms living within our gut microbiome. Most provide benefits for the body’s health; others can promote illness and disease. A healthy microbiome maintains a diverse, balanced composition of microbiotic life. When that balance is upset, the body may be at greater risk for disease.
  • The make-up and the diversity of organisms within the microbiome—both the types and amounts of different bacteria and other microbes—appear to have a profound effect on mental and physical health, influencing mood, metabolism, cardiovascular and circulatory health, immune system functioning, and our risk for chronic disease.

In search of an explanation for the broad effects that sleep has on these same chronic and serious health conditions, researchers in this latest study went looking for an answer to the question, how is the microbiome affected by circadian rhythms? They focused their investigation specifically on a type of immune cells that are located in the gut.

These cells perform a number of critical functions, including:

  • Helping to control the composition of the microbiome
  • Regulating metabolism
  • Limiting inflammation
  • Protecting the gut from infection
  • Keeping the lining of the gut strong (and avoiding a so-called “leaky gut)

Like most other cells throughout the body, these immune cells in the gut contain genes that control circadian bio rhythms. Immune function, in the gut and throughout the body, operate within a 24-hour circadian cycle. All the circadian activity of the body—from immune functioning, to metabolic activity, and cycles of eating and sleeping—are synchronized by a master bio clock located in the brain. That master clock communicates with the “clock genes” located in cells all throughout the body. Those cell-placed clock genes keep time for the specific activity of each type of cell.

This new study made a couple of really important discoveries. Scientists learned that these immune cells, which do so much to keep the gut microbiome healthy and strong, and the immune system functioning optimally, are highly influenced by shifts in circadian rhythm activity, via changes to their clock genes. Scientists also discovered a direct communication pathway between the brain’s master bio clock and these gut microbiome immune cells. In their study of mice, researchers found that when circadian rhythms directed by the brain’s master clock were disrupted, there was a significant impact on the gut microbiome. Among the changes? The balanced composition of microbes was disrupted, inflammation increased, and the intestines became more prone to infection. Metabolic activity also suffered.

What disrupted mice circadian clocks and compromised the communication between the master bio clock and these immune cells? Some of same things that disrupt circadian rhythms in humans, including exposure to light at night and irregular eating patterns. Sleeping on variable schedules, rather than maintaining consistent bed and wake times, also disrupts the body’s circadian bio clocks. 

 This isn’t the first research to show ways that the human microbiome is regulated by circadian rhythms. Other research has demonstrated that when circadian rhythms are disrupted, the health and functioning of the microbiome suffers.

The takeaway?  This is some crucial new detail how deeply sleep and circadian rhythms appear to affect the health and functioning of the gut. Sticking to a sleep routine, limiting nighttime light exposure, managing stress, and practicing healthy, sleep-friendly eating habits are all ways to keep your circadian clock—and your gut microbiome—functioning optimally.

Interested in learning more about the microbiome, and how it relates to sleep? I’ve written about this topic here, and here. To learn more about how your bio rhythms affect your sleep, your health, and your performance in just about every way imaginable, check out my book, The Power of When.

Sweet Dreams,

Michael J. Breus, PhD

The Sleep Doctor™

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