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核心提示:When it comes to weight gain, the timing of your meals may be just as important as what or how much you eat. According to a study of lab animals published online by the journal Obesity, eating during the hours that the body would naturally be sleepi

    When it comes to weight gain, the timing of your meals may be just as important as what or how much you eat. According to a study of lab animals published online by the journal Obesity, eating during the hours that the body would naturally be sleeping may lead to excess weight gain.

    In the first study to associate meal timing with degree of weight gain, sleep scientists at Northwestern University compared two groups of mice, each placed on opposite feeding schedules for a six-week period. Both groups were fed the same high-fat food, and both had the same amount of daily physical activity. The only difference: one group was fed during its normal 12-hour waking period, while the other rodents where fed while they should have been asleep. By the end of the study period, the latter group had gained more than twice as much weight as the mice that ate during active hours: 10.4 g, a 48% increase in body weight, versus 4.4 g, or a 20% gain in baseline weight.

    "For a long time we questioned whether or not eating patterns had anything to do with gaining weight," says obesity expert Dr. Louis Aronne of NewYork-Presbyterian Hospital/Weill Cornell Medical Center. He points to previous observational research suggesting that people who skip breakfast in favor of massive meals in the evening hours tend to be overweight. "We had no proof that it's a real problem," says Aronne, who was not involved in the study. "If an experiment like this is replicated in humans, it might clarify for us just how much time of day matters when it comes to obesity."

    The salient issue, says study co-author Fred Turek, may be the disruption of the body's internal clock, known as the circadian rhythm. Eating at inappropriate times may disturb the body's natural rhythm, setting off a string of metabolic reactions that ultimately lead to weight gain. "Because our bodies are naturally cued to eat at certain times of the day, dining at the wrong time might affect the body's ability to maintain its energy balance," he explains, meaning that our body starts to use its calories differently than it normally would. That in turn could cause fluctuations in numerous hormones, including an increase in ghrelin and a decrease in leptin - the two key hormones that govern appetite and satiety. The hunger hormone ghrelin, which is produced by the stomach, sends a "feed me" message to the brain; leptin, the satiety hormone, signals the brain to stop eating.

    But while these hormones have been successfully manipulated in lab mice to prompt weight gain or loss, the same has not been true in humans. Experiments in which obese human patients were injected with leptin have failed, because the metabolic pathways that control hunger and fullness in people are far more complex than they are in mice. Knocking out one of, say, 50 such pathways through drug treatment just means the other 49 will eventually pick up the slack, says Dr. George Fielding, a bariatric surgeon at the NYU Program for Surgical Weight Loss.

    Although the new findings in Obesity cannot yet be applied outside the lab, other research supports the idea that the disruption of sleep (that includes standing in front of the fridge eating chicken at 2 a.m.) may have something to do with weight gain in humans. Studies of night-shift workers like nurses and factory workers indicate they are at higher risk for being overweight than their daylight counterparts, partly due to poor sleep routines and partly because of their tendency to eat heavy meals late at night, says Aronne. Other studies show that people who get a full eight hours of sleep at night tend to be thinner than those who get less, while numerous epidemiological studies have established a link between short or poor sleeping patterns with overweight-related conditions including diabetes and cardiovascular disease.

    Until future studies in humans bear out Turek's preliminary findings, Aronne suggests that avoiding post-dinner snacking is probably still a good strategy, regardless of size. Not only could it help prevent extra weight gain, it can also lower the risk of gastroesophageal reflux and other digestive problems that may compound sleep problems. Aronne further recommends taking well-balanced and evenly spread meals throughout the day, rather than consuming 50% or more of your daily calories at dinner or afterward, since that may also lead to unwanted pounds.








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