My hubby reads our local paper’s Health + Science section religiously and often finds nutrition articles he wants my take on. When he handed me this one, Keeping Calories on the Clock, which discusses the impact our circadian rhythms have on metabolism, he didn’t merely suggest I read it – he insisted. Good call, Honey.
Circadian rhythms are fascinating. According to some quick research I did, it appears scientists first began studying circadian rhythms in the 1970’s, thanks to some interesting mutations they observed in the lowly fruit fly that led them to identify an internal 24-hour “rhythm” or “biological clockwork” within each of us. But even though scientists have known about these internal 24-hour rhythms since the 70’s, many mysteries have remained regarding the impact and influence circadian rhythms have on our health.
Fast forward to the year 2017 and you may remember the Nobel Prize in Physiology/Medicine went to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their discoveries of “molecular mechanisms controlling the circadian rhythm.” It turns out those fruit flies had some very important teachings for us.
Most people already know that circadian rhythms seriously impact sleep cycles and the quality of our sleep, but this “clockwork within our cells” impacts much more than just sleep. The article I’m sharing with you discusses how circadian rhythms also impact our metabolism. For those of us in nutrition, this is important news to share with the world. It reinforces what we’ve know for a long time – it’s not just about “what” you eat, “when” you eat also matters. If we don’t fall into step with the rhythm our body has set for us, we could be sabotaging our efforts at maintaining a healthy weight.
It’s a pretty quick read. Enjoy.
Keeping Calories on the Clock:
We’re hard-wired to eat at key times; Ignoring that can raise health risks.
By Melissa Healy, of the Los Angeles Times, reprinted in Star Tribune
Next time you stagger into a Waffle House in the wee hours of the morning and order the Texas sausage egg & cheese melt (1,040 calories), consider this new research finding: At roughly that hour, the most basic operations of the human body throttle back their caloric needs by about 10 percent compared to the rate at which they will burn calories in late afternoon or early evening.
Maybe you’d prefer to come back around dinnertime.
This pattern of calorie use doesn’t significantly vary based on whether you’re the server working the graveyard shift, or a 9-to-5er stopping in for breakfast after eight hours of shut-eye, the researchers found. Humans’ “resting energy expenditure” – the body’s use of calories to power such basic functions as respiration, brain activity and fluid circulation – follows a predictable cycle that waxes as the day progresses and wanes as night sets in.
The study, published in the journal Current Biology, offers evidence that circadian rhythms dictate not just when we feel the urge to sleep but how complex mechanisms like metabolism operate across a 24-hour period. It may help explain why people who keep irregular sleep schedules, including swing shift workers, have higher rates of obesity and are more likely to develop metabolic abnormalities such as type 2 diabetes.
And it demonstrates that whether we hear it or not, our body’s clock is always ticking, locating us in our daily cycle with uncanny precision.
At “hour zero” – roughly corresponding to somewhere between 4 and 5am – our core body temperature dips to its lowest point and our idling fuel use reaches its nadir. From that point, the body’s “resting energy expenditure” rises until the late afternoon/early evening. After reaching its peak at roughly 5pm, the number of calories we burn while at rest plummets steadily for about 12 hours.
And then, we start again.
These new findings are a reminder that no matter how 24/7 our schedules have become, our bodies were built for a slower, simpler world in which humans moved around all day in search of food, ate while the sun was up, and slept when the sky was dark.
Today, our appetites and the all-night availability of food may induce us to eat well after sundown. And our jobs may demand that we sleep during the day and care for our patients or drive trucks through the night. But our bodies still adhere to their ancient, inflexible clocks.
The findings also come with an implicit warning: When we disregard the biological rhythms that rule our bodies, we do so at our peril.
Resting energy expenditure accounts for the majority of the minimum calories we burn in a day. Just to spend a day eating, sleeping and breathing uses 60 to 70 percent of our “resting energy expenditure.” So a serious mismatch in the time when calories are consumed and the time when most of them are burned could prompt the body to make decisions – like sorting calories as fat – that aren’t necessarily healthy.
The study adds to a growing body of evidence suggesting that a good 12-hour fast, when aligned with darkness and our bodies’ nocturnal response, may be a way to prevent or reverse obesity. In lab animals and a growing number of people, Salk Institute researcher Satchin Panda has demonstrated the impact of dietary obedience to our circadian rhythms.
Others have demonstrated the power of timing by showing how readily it can be disrupted. In a 2014 study, 14 lean, healthy adults agreed to turn their days upside-down over a six-day period. Fed a diet sufficient to maintain their weight, the subjects quickly adapted by turning their thermostats down. Compared to the baseline readings taken upon their arrival (when they were awake by day and asleep eight hours at night), the subjects burned 52 fewer calories on day 2 of their swing-shift schedule, and 59 fewer calories on day 3 of that schedule.
Do that for a couple days and you might feel a little off. Do it for months, years, or a lifetime and the result could be metabolic processes that go haywire.
“One takeaway is indeed that for optimal health, including metabolic health, it’s best for us to have a regular schedule seven days a week – getting up and going to bed at the same time and eating our meals at the same time, “ said senior author Jeanne F. Duffy, a neuro-scientist and sleep specialist at Brigham & Women’s Hospital in Boston. “We have these powerful clocks in ourselves.”
When we sleep late on weekends, hopscotch across time zones, or work on schedules that have us up all night then back on the day-shift, “we’re disrupting our clocks and making our metabolisms inefficient, and in the long term, that will lead to disease,” she said. “Staying on the same schedule is the best way to prevent that.