Recalibrating Calorie Intake and Energy Expenditure

"It's not only what we eat, but when we eat -- and rest -- that impacts how much energy we burn or store as fat."
"The vast majority of the calories that we burn every day [60 to 70 percent] are burned just to maintain our body functions."
"If you ate at the wrong biological time once, it wouldn't have much impact. [More frequently than occasionally] it could add up over time and lead to weight gain." 
"Let’s say we get up an hour or two hours early and eat breakfast an hour or two hours early. We may be eating that breakfast not only at a time when our body might not be prepared to deal with it, but at a time when we need less energy to maintain our functions. Therefore, the same breakfast might result in extra stored calories, because we don’t need those to maintain our body functions."
"Regularity of habits such as eating and sleeping is very important to overall health."
Dr. Jeanne Duffy, neuroscientist, sleep and circadian disorders, Brigham and Women's Hospital

"The fact that doing the same thing at one time of day burned so many more calories than doing the same thing at a different time of day surprised us."
Kirsi-Marja Zitting, study co-author, Brigham and Women's Hospital and Harvard Medical School

A new study finds that an imbalance between one’s circadian rhythm and eating and sleeping habits may contribute to weight gain. (Credit: Pakula Piotr/Shutterstock)

Biological sciences keep coming up with interesting items to explain processes that might otherwise forever appear inexplicable to us about how our bodies work. As was done when researchers from Boston launched their experiment with seven volunteers. The seven participants in the study were kept for 37 days in windowless rooms where there were no clocks, radios, televisions, phones or Internet. No distractions, nothing to inform the participants of what was happening in the world outside their temporary cocoon.

Everything was geared to perfect conformity in timing; bedtimes adjusted so that study participants went to sleep each night four hours later than they normally would, the effect disturbing their body's natural circadian rhythms in a manner they likened to the effect of an flight from England to Halifax one day then the following day on to Vancouver, followed by a trip to the Marshall Islands the third day and the fourth day on to Hong Kong.

The study, published in the journal Current Biology, found that at rest the human body burns ten percent more calories in late afternoon and early evening than it does in the early morning hours. A conclusion that explicates why night- or rotating shift-work can effect the risk of becoming overweight or obese. Resting energy expenditure (REE) was the focus to determine the number of calories the body burns simply to exist -- reflecting the minimum amount of calories required in the maintenance of physiological functions such as circulation of blood, breathing, body temperature and brain activity.

The researchers investigated whether resting energy expenditure rate varies with circadian rhythms representing the body's innate, 24-hour cycle set to control the body's awareness of day and night, and when to eat and when to sleep. The 37 days the volunteers -- aged 38 to 69 -- spent in chambers free of any distractions much less indications of time, enabled them to read, watch videos or DVDs, but enjoy no visitors. Contact with family or friends conducted through mail only.

All subjects were given the same proportion of protein, carbohydrates and fats; body temperatures monitored with rectal sensors (more calories are burned when the core temperature is highest).

For their time and willingness to surrender such a large amount of their time and free agency, study participants were given an award of $12,000 each. Each night for three weeks the assigned bedtime was moved four hours later than that of the night before to confuse the normal circadian rhythms. During scheduled "sleep opportunities" all lighting was switched off, the process enabling researchers to take measurements across each waking period for the duration of the three weeks.

"So that we could get an idea of whether resting energy expenditure was always the same no matter what biological time they woke up at, or whether it varied", explained Dr. Duffy. It was discovered that the amount of calories burned turned out to be lower during late night, corresponding to the dip in core body temperature, and highest 12 hours later which would relate to the equivalent of late afternoon or early evening.

While the study answered some questions, there are others yet to be approached by further studies. It is not known whether people should be timing meals to late afternoon-early evening peak, or whether they might be better off avoiding meals after early morning workouts at a time when resting calorie burn is at its lowest. The researchers estimated that about 130 calories per day is involved in the difference between peak and minimum calorie burn time.

Photo Taken In Bangkok, Thailand (Getty Images)