单选题   We are what we eat, and now researchers are saying that our diet affects how we sleep. A study, published in the journal Appetite, found differences in the diets of people who slept for seven to eight hours a night compared with those snoozing for five. Since less sleep is associated with high blood pressure, poorer blood-glucose control (increasing the risk of diabetes) and obesity (as is more sleep in some studies), shouldn't we eat the foods that are most likely to help us sleep a healthy amount? And does anyone know what foods these are?
    The study in Appetite used data from the US National Health and Nutrition Examination Survey and found that those who slept the standard seven to eight hours ate the greatest variety of foods. Those who slept the least (less than five hours) drank less water, took in less vitamin C, had less selenium (硒) (found in nuts, meat and shellfish) but ate more green, leafy vegetables. Longer sleep was associated with more carbohydrates, alcohol and less choline (胆碱) (found in eggs and fatty meats) and less theorbomine (茶碱) (found in chocolate and tea). The researchers took into account other factors such as obesity, physical activity and income, and still found these differences in diet.
    They concluded that both long (nine hours-plus) and short sleep are associated with less varied diets but say they don't know if changing diet would affect how long we sleep for. The study shows only an association, although the link with short and long sleep both being 'unhealthy' holds true with a 2011 review of evidence about the length of sleep and risk of heart disease.
    The evidence on what diet would help us sleep best isn't clear. It is also not evident how much individual preferences for sleep—some like to sleep longer than others—affect these results. But there is more research on the relationship between sleep and weight, with studies showing the shorter the amount of sleep a person has, the hungrier they feel.
    A German study presented at the Annual Meeting of the Society for the Study of Ingestive (摄食的) Behaviour last year showed that after just one night of sleep disruption the volunteers in the study were less energetic (so used up fewer calories) but hungrier. The researchers said their volunteers also had raised blood levels of ghrelin (胃饥饿素), a hormone linked to the feeling of hunger. A commentary a few months later in the Journal of the Canadian Medical Association backed this association, saying that while encouraging a weight-loss regime of eating less, moving more and sleeping more might be too simplistic, diets were helped by good amounts of high quality sleep.
    So while no one knows what foods will stop you waking up at 5 am, you won't go wrong with a more varied diet and a sensible bedtime.

单选题     What can we learn from the first paragraph?

单选题     What can we learn from the second paragraph?

单选题     What does the 2011 review indicate?

单选题     According to the fourth paragraph, it is clear that ______.

单选题     What does the German study find?