By Christopher Pearson
Health ministers, state and federal, are of one mind on the question of obesity. Lack of exercise and poor diet (known in the trade as the Big Two) are to blame. Recent articles in the International Journal of Obesity tell a different story.
Pathways, an obesity prevention program associated with the Johns Hopkins school of public health, ran a three-year study on Native American children. Improved diet and more exercise did not lead to any significant difference in body mass index between the youngsters who participated in the program and the control group. As well, there's a marked paucity of experimental evidence to support the proposition that lack of exercise and too much junk food cause obesity. Not for the first time, medical science has been artlessly assuming that which had to be proved.
The trailblazing IJO article (by S. W. Keith, D. T. Redden et al) concludes that: "Undue attention has been devoted to reduced physical activity and food marketing practices as postulated causes for increases in the prevalence of obesity, leading to neglect of other plausible mechanisms and well-intentioned, but potentially ill-founded, proposals for reducing obesity rates." They suggest no fewer than 10 other possible causes.
Given that being overweight is usually attributed to the sins of gluttony and sloth, these are tidings of comfort and joy just when we needed them, on the eve of a protracted period of feasting. If you've been feeling guilty in advance about all that succulent ham on the bone, roast pork with extra crackling and Christmas pudding with brandy butter, forget it and let your joy be unconfined. Thanks to the IJO, those of a fuller figure can confidently tell the Fat Police to mind their own business and eat to their heart's content. I've been doing so for years now, on the grounds that it's not what you eat or the exercise you miss out on for the festive season but year-round habits that make the difference. But this Christmas there'll be 10 more strings to my bow.
The first blameless cause of obesity is lack of sleep. The evidence from the First World is that since 1960 the average amount of sleep we get has declined by about 90 minutes The researchers say unhealthy sleeping habits potentially have as much effect on our body weight as junk food. There's solid evidence to demonstrate the connection between lack of sleep and BMI, not only in rats but in human beings. Levels of leptin, the hormone that tells the brain that the stomach is full, decrease in the sleep-deprived, and ghrelin, the hormone that prompts hunger, increases. If you want to lose weight, the trick might be not to engage in strenuous exercise but make sure you get a good eight hours of shut-eye.
Another blameless and well-established cause of obesity is man-made poisons that have found their way into the food chain. One indicator the research identifies is polybrominated diphenyl ether. Apparently it almost doubled every five years in Swedish mothers' breast milk between 1972 and 1998. DDT, which is known to increase the fatty tissue in laboratory rats, is also a contender, known to affect human hormone systems.
Natural hormonal changes are responsible for puppy fat in young children and for post-menopausal women's weight gains. There are also various medications that can drastically affect fluid retention and BMI. If you've put on weight recently, it may well have been because of new drugs for diabetes, blood pressure, depression, allergies or oral contraceptives. If, like a good many middle-aged people, you suffer from more than one of those afflictions, it's quite likely they compound the weight problem. Beta-blockers induce a mean weight gain of approximately 1.2kg. One study of oral contraception estimated a mean weight gain of 5kg after two years.
If taking medications is an example of blameless weight gain, then giving up smoking must surely count as conspicuous virtue. Yet there is no surer way to put on weight. Nicotine is a powerful appetite depressant. The best estimate on offer is that between 1978 and 1990, stopping smoking was responsible for about a quarter of the increase in the prevalence of overweight in men and about one-sixth of the increase in women.
Another factor contributing to obesity, in which none of us has any say, is the age at which our mothers bore us. A study of 10-year-old girls found that the odds of obesity increased by more than 14 per cent for every five-year increment in maternal age. Sociological factors such as the propensity to spoil late-arriving children may play a part but there's a biological correlation in sheep between maternal age and fat deposition related to uncoupling protein levels. The mean age of mothers at birth has been inexorably increasing globally since 1960. Another cause for increased obesity levels in the US lies in changes in the distribution of ethnicity and age. "Compared with young European Americans, middle-aged adults, African-Americans (when comparing women only) and Hispanic Americans have a markedly higher obesity prevalence." The increase of Hispanic American adults as a proportion of the population from 5 per cent in 1970 to about 13 per cent in 2000, and a 43 per cent increase in adults aged between 35 and 44 over the same period, argue for a small but statistically significant factor.
Air-conditioning is one explanation for the obesity epidemic, which is very much a late 20th-century First World phenomenon. Exposure to ambient temperatures either above or below the comfort zone "increases energy expenditure, which, all other things being equal, decreases energy stores that is, fat". If you've ever felt that extremes of hot or cold were enervating and left you hungry, that's why.
The most obvious of the blameless components to stoutness is heredity. The heritable component "is well supported by animal breeding studies and human twins, family and adoption studies with an estimated heritability of approximately 65 per cent". There is also a compounding factor over the generations. There's evidence that fatness is associated with greater reproductive fitness, which leads to natural selection of obesity-disposed genotypes.
Last but not least, Father Ephraem Chifley, sometime food reviewer at The Adelaide Review, has drawn my attention to another IJO article (S. D. Vangipuram, M. Yu et al). The human adenovirus Ad-36 causes obesity by reducing leptin expression and secretion and increasing glucose uptake by fat cells. As Chifley remarked: "The moral vanity of the authoritarian and lean is far from being the answer to obesity. It is gratifying for some to think that the fat problem can be solved by boot camps and by the stigmatisation of the overweight. The idea that you might be able to catch obesity as easily as you can the common cold should give us all pause for thought."
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