DEAR DR. BLONZ: Assuming I will eat the same number of calories from the same types and amounts of foods, is it better for me to have those calories earlier in the day, or later? -- A.C., Dallas
DEAR A.C.: There is a bit of evidence that a calorie may have varying effects when consumed at different times of the day. A classic 1976 study by professor Franz Halberg had volunteers consume only meal per day, either as their breakfast or their dinner. The participants adapted to the new routine and reported hunger pangs prior to their scheduled meal.
All things considered, those who had their meal at dinnertime were more likely to gain weight than those having their calories in the morning. The body, it seems, is more likely to use more calories when they're consumed earlier in the day.
There is some logic here, given that the one meal represents the entire day's energy intake. The full-day calorie supply entering the body after a morning meal will need to be portioned out to the energy-requiring activities of the day, as well as toward storage. Contrast this with a full-day's calorie supply being absorbed after an evening meal, with the evening's tapering energy demands. This creates more of an uninterrupted flow toward calorie storage.
The science that studies such time-related issues was first named chronobiology (chrono meaning "time"), but was more recently dubbed chronomics. It began in the early 1700s when botanists discovered that plant behavior adhered to a daily cycle. Since then, scientists have identified rhythmic behaviors in animals, and research continues on rhythms in the human body.
It has been learned, for example, that bodily events such as blood pressure, body temperature, heart rate and urine excretion all have distinct daily rhythms. Cycles that occur on a 24-hour basis are called circadian rhythms, but there are also those that are weekly, monthly or yearly. It helps explain hunger pangs, jet lag or even a ritual daily visit to the bathroom. Research is telling us that the patterns may provide a clue as to how nutrition could best serve us in the prevention and treatment of many ailments.
Optimizing meal timing can have implications for numerous groups of people: the elderly who find it difficult to eat large meals; pregnant or lactating women with limited food resources; athletes in training, seeking to foster muscle growth; or dieters continually baffled by their bodies' resistance to giving up excess weight. Other possibilities would include the most efficient timing of meals in relation to radical treatments, such as chemotherapy.
There's little question that research in this area may unlock many of the body's mysteries. Science once tended to gloss over the time factor, but an awareness of chronomics might provide tools to better understand the body's elusive rhythms.
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