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Circadian Rhythms: Why Big Meals at Night Make Us Fat

 Do you consider yourself to be a morning person or an evening person? Do you load most of your calories into the end of the day? If so, listen up because this newsletter is for you.

An interesting study done in Spain reported that consuming the majority of calories later in the day slows down weight loss. Four hundred overweight individuals were into two groups, based on when they ate their largest meal, which in Spain happens to be lunch. Those who ate lunch before 3 pm were “early eaters” and those who ate after 3 pm were “late eaters”. At the end of the 20-week study it was found that the early eaters lost 25 percent more weight. When calories and exercise were analyzed – there was little difference between the groups. What accounted for the difference then?

Circadian Rhythms
The rotation of the earth around its axis imparts light and dark cycles of 24 hours. Organisms on earth developed the ability to predict these cycles and evolved the ability to restrict their behavior to day or night, becoming diurnal or nocturnal, respectively. All plants and animals have an inherent circadian rhythm. With this adaptation, plants and animals ensure physiological processes are performed at the optimal time. In mammals, circadian rhythms influence all behavior, sleep-wake cycles, cardiovascular processes, body temperature, hormone release, digestion, and liver metabolism.

Circadian rhythm in the human body is determined by a region deep within our brain, the suprachiasmatic nucleus of the hypothalamus. Responding to the signal of light, this master clock sends thousands of signals to the organs of the body as to whether they should be active or inactive.

What happens when we sleep? At rest, heart rate slows. Levels of stress hormones – cortisol, norepinephrine and epinephrine - fall as we relax. Melatonin, the sleep hormone, is released inducing sleep. Core body temperature is lowest during sleep as blood flow is directed towards the warming of our inactive extremities by the secretion of melatonin. Growth hormone is released during deep sleep, allowing repair of muscle damage and consolidation of memories. Leptin, the fat cell hormone, peaks during sleep, informing the brain of nutrition status. Insulin levels fall as melatonin increases insulin sensitivity in cells. During the night, we are programmed to sleep, allowing the body to rest and repair.

Consuming the majority of calories late at night forces the release of digestive enzymes and hormones, raising core body temperature. As food is digested insulin, the fat storage hormone, is released. By eating a large meal late in the day the body will store calories as fat rather than metabolize them for energy. Skipping meals to “save” calories for the evening meal works against our basic biology. My motto: At night, keep it light!
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