The balance between weight gain and weight gain loss
is predominantly determined by what you eat, how much you eat, and by how much
exercise you get. But another important factor is often neglected... it's not
just how many calories you eat, but WHEN you eat them that will determine how
well you burn those calories.
The balance between weight gain and weight gain loss
is predominantly determined by what you eat, how much you eat, and by how much
exercise you get. But another important factor is often neglected... Published
February 27 in the open-access journal PLOS Biology, research conducted by
Kevin Kelly, Owen McGuinness, Carl Johnson and colleagues of Vanderbilt
University, USA shows that it's not just how many calories you eat, but WHEN
you eat them that will determine how well you burn those calories.
Your daily biological clock and sleep regulate how the
food you eat is metabolized; thus the choice of burning fats or carbohydrates
changes depending on the time of day or night. Your body's circadian rhythm has
programmed your body to burn fat when you sleep, so when you skip breakfast and
then snack at night you delay burning the fat.
The researchers monitored the metabolism of mid-aged
and older subjects in a whole-room respiratory chamber over two separate
56-hour sessions, using a "random crossover" experimental design. In
each session, lunch and dinner were presented at the same times (12:30 and
17:45, respectively), but the timing of the third meal differed between the two
halves of the study. Thus in one of the 56-hour bouts, the additional daily
meal was presented as breakfast (8:00) whereas in the other session, a
nutritionally equivalent meal was presented to the same subjects as a
late-evening snack (22:00). The duration of the overnight fast was the same for
both sessions.
Whereas the two sessions did not differ in the amount
or type of food eaten or in the subjects' activity levels, the daily timing of
nutrient availability, coupled with clock/sleep control of metabolism, flipped
a switch in the subjects' fat/carbohydrate preference such that the
late-evening snack session resulted in less fat burned when compared to the
breakfast session. The timing of meals during the day/night cycle therefore
affects the extent to which ingested food is used versus stored.
This study has important implications for eating
habits, suggesting that a daily fast between the evening meal and breakfast
will optimize weight management.
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