When it comes to healthy living, there’s no shortage of competing views on how to fight flab, run faster, sleep sounder and feel happier.

But what if when you exercise — and eat and sleep — is just as important as how?

Mounting evidence suggests that our bodies perform differently at different times of the day. Like all living things, we have an internal clock that affects our hormonal responses, body temperature, heart rate and sleep cycles. It’s determined by something called circadian rhythms, which follow the 24-hour pattern of the Earth’s rotation.

Does this sound a bit mystical? Maybe. But health experts say knowing your body’s clock can help you synchronize your daily activities for optimal health. Mastering these internal rhythms can pay dividends — from controlling your weight to sleeping better to improving your overall mood.


“Whether you are a yeast in beer or a fly or a dog or a fish, we all have this innate 24-hour circadian rhythm,” said Dr. Michael Howell, a neurologist at the University of Minnesota. “What your body is doing at 8 o’clock in the morning is different than what your body is doing at 10 o’clock in the morning. Your gut responds differently to food at different times of the day, and we have different capacities for exercise at different times of the day.”

What happens if you disrupt these natural rhythms? You might be setting yourself up for a host of health problems.

The well-timed sleep

For many people, a good night’s sleep is the hallmark of optimal health.

There’s no perfect time to wake up, Howell said, because sleep cycles vary dramatically from person to person. But finding the time when you naturally wake up is crucial to getting good rest. Sleep problems more often stem from mistimed sleep than from anything else.

Nighttime, Howell said, isn’t the only time our bodies crave sleep. Our energy level and body temperature takes a natural dip in the middle of our waking day, making us tired. Before industrialization, most people did not work a conventional eight to nine hours in a row without pausing for rest, he said.

Although most modern work schedules do not make it possible to accommodate a midafternoon power nap, the most refreshing sleep comes from having slept six hours at night and then napping for up to two hours in the afternoon, Howell said.

Nap times vary, depending on when you get up in the morning. “It’s usually 6 hours after your normal wake-up time,” he explained, “so if you wake up at 7 a.m. then your natural time to fall asleep is at one in the afternoon.”

Fitting in fitness

Martha Mattheis, a lawyer from Carver County, is an avid long-distance runner and has completed 17 marathons. She enjoys running in the morning, but has tried running at different times of the day.

She’s made a discovery: “I think I run faster in the afternoon,” she said, “because I am warmed up and I’ve had quite a load of caffeine on board.”

Some physiologists back up the idea that afternoons are the perfect time to tackle high-intensity exercise.

“That’s because you have the day to warm up as opposed to waking up with stiff joints, and blood flow [in the morning] might not be quite what it is at the end of the day,” said Paul Mellick, assistant professor in the Department of Health and Human Performance at the University of St. Thomas.

Yet some trainers and fitness coaches say people should just keep it simple: The best time to exercise is whenever works best for you. “As a physiologist, I don’t care when you do it. Just do it,” said Mark Blegen, chair of the Exercise and Nutrition Sciences department at St. Catherine University.

Blegen prefers to exercise in the morning.

When to fuel up

When it comes to eating, experts differ on timing.

“From a scientific standpoint, there have been studies that say eating smaller meals, more frequently can be beneficial. So, eating every two hours,” said Katherine Zeratsky, a registered dietitian with the Mayo Clinic in Rochester. “There’s equivalent research that says eating three meals is adequate.”

But they’re unanimous on the importance of breakfast. It keeps your mind sharp and can prevent overeating later. Some say you should eat within an hour of waking up, while others say within two hours is ideal.

So when should you stop eating for the day? Many diets ban foods after 7 p.m. as a way to discourage snacking on unhealthy foods. Sleep experts say eating late at night, especially anything with caffeine, will raise your heart rate and prevent you from falling asleep on time. But some nutritionists see little harm in eating past 7 p.m. and one even recommends having a healthy snack an hour before sleeping.

“This is where we might differ from a lot of people,” said Darlene Kvist, founder of Nutritional Weight and Wellness in the Twin Cities. “We believe that an hour before you go to bed, you need to have a snack with a little fat and a little bit of carbohydrates. The fat helps to stabilize blood sugars through the night so [people] sleep more soundly and deeper and they’re more rested in the morning.”

Indeed, early risers stand to benefit from several wellness pursuits timed perfectly for the morning hours.

Erik Storlie teaches meditation at the University of Minnesota’s Center for Spirituality and Healing, where his students often ask “when should I meditate?” He tells them that they must find their own optimum time, but generally, one of the best times is when you wake up — when the world is quiet. He also suggested pausing in the middle of the day, and just before you lay your head on the pillow at night.

The body’s inner clock can even help you perform better in other, more surprising, wellness areas.

Levels of oxytocin, also called the “love hormone,” are highest in the morning hours. Men’s testosterone levels also peak early in the day.

When it comes to having great sex, it seems, everyone should be a morning person.