Ask anyone why there is an obesity epidemic and they will tell you that it’s al down to eating too much and burning too few calories. That explanation appeals to common sense and has dominated efforts to get to the root of the obesity epidemic and reverse it/ yet obesity researchers are increasingly dissatisfied with it. Many now believe that something else must have changed in our environment to precipitate(促成) such
dramatic rises in obesity over the past 40 years or so. Nobody is saying that the “big two” – reduced physical activity and increased
availability of food – are not important contributors to the epidemic, but they cannot explain it all.
Earlier this year a review paper by 20 obesity experts set out the 7 most plausible alternative explanations for the epidemic. Here they are.
1. Not enough sleep
It is widely believed that sleep is for the brain, not the body. Could a shortage of shut-eye also be helping to make us fat?
Several large-scale studies suggest there may be a link. People who sleep less than 7 hours a night tend to have a higher body mass index than people who sleep more, according to data gathered by the US National Health and Nutrition Examination Survey. Similarly, the US Nurses’ Health Study, which tracked 68,000 women for 16 years, found that those who slept an average of 5 hours a night gained more weight during the study period than women who slept 6 hours, who in turn gained more than whose who slept 7. It’s well known that obesity impairs sleep, so perhaps people get fat first and sleep less afterwards. But the nurses’ study suggests that it
can work in the other direction too: sleep loss may precipitate weight gain.
Although getting figures is difficult, it appears that we really are sleeping less. In 1960 people in the US slept an average of 8.5 hours per night. A 2002 poll by the National Sleep Foundation suggests that the average has fallen to under 7 hours, and the decline is mirrored by the increase in obesity.
2. Climate control
We humans, like all warm-blooded animals, can keep our core body temperatures pretty much constant regardless of what’s going on in the world around us. We do this by altering our metabolic(新陈代新的) rate,
shivering or sweating. Keeping warm and staying cool take energy unless we are in the “thermo-neutral zone”, which is increasingly where we
choose to live and work.
There is no denying that ambient temperatures(环境温度) have changed in
the past few decades. Between 1970 and 2000, the average British home warmed from a chilly 13C to 18C. In the US, the changes have been at the other end of the thermometer as the proportion of homes with air conditionings rose from 23% to 47% between 1978 and 1997. In the southern states – where obesity rates tend to be highest – the number of houses
with air conditioning has shot up to 71% from 37% in 1978. Could air conditioning in summer and heating in winter really make a difference to our weight?
Sadly?there is some evidence that it does-at least with regard to heating. Studies show that in comfortable temperatures we use less energy.
Bad news: smokers really do tend to be thinner than the rest of us,and quitting really does pack on the pounds, though no one isn sure why. It probably has something to do with the fact that nicotine is an appetite suppressant and appears to up your metabolic rate.
Katherine Flegal and colleagres at the US National Center for Health Statistics in Hyattsville,Maryland, have calculated that people kicking the habit have been respousible for a small but significant portion of the US epidemic of fatness.From data collected aroud 1991 by the US National Health and Nutrition Examination Survey,they worked out that people who had quit in the previous decade were much more likely to be overweight than smokers and people who had never smoked .Among men, for example, nearly half of quitters were overweight compared with 37% of non-smokers and only 28%of smokers.
4. Genetic effects
Yours chances of becoming fat may be set,at least in part,before you were even born.children of boese mothers are much more likely to become obest themselves later in life.Offspring of mice fed a high-fat diet during pregnancy are much more likely to become fat than the offspring of identical mice fed a normal diet. Intriguingly,the effect persists for two or three generations.Grand-children of mice fed a high-fat diet grow up fat even if their own mother is fed normally-so you fate may have been sealed even before you were conceived.
5.A little older„
Some groups of people just happen to be fatter than others.surveys carried out by the US national center for health statisties found that
adults aged 40 to 79 were around three times as likely to be obese as younger people.non-white females also tend to fall at the fatter end of the spectreum:Mexican-american women are 30% more likely than white women to be obsess,and black women have twice the risk.
In the US,these groups account for an increasing percentage of the population.between 1970 and 2000 the US population aged 35 to 44 grew by 43%.the proportion of Hispanic-americans also grew,from under 5% to 12.5% of the population,while th