Berkeley, CA, Nov. 23, 2011--America’s waistline has been expanding at an accelerating rate, prompting both concern about the nation’s health and puzzlement over the cause. Now a researcher at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has come up with some intriguing new data and a provocative hypothesis: that obesity itself makes people much more susceptible to risk factors that promote weight gain in the first place.
New research published in the journal PLoS One by Paul T. Williams, a staff scientist and biostatistician at Berkeley Lab, depicts a vicious circle -- what researchers call a positive feedback loop -- in which weight gain itself creates conditions that amplify vulnerability to well-established drivers of obesity. WIlliams contends that this phenomenon may be the root cause of America’s runaway weight problem. "We are getting fatter because we are fat," he says. "It’s depressing, isn’t it?"
As Thanksgiving and the holiday season approaches, people tend to be more conscious of their overeating and weight gain. With this latest study, there is now more statistical evidence to back the common perception that the heavier you become, the harder it is to control weight. "These findings suggest that people should start worrying about a weight-loss program when they are still lean,’’ says Williams. "But of course, nobody does that." Williams says he is no exception. He recently cut his food portions in half, and shed 31 pounds.
His latest findings, however, are ammunition for those who favor more vigorous efforts to reduce the risk of obesity where possible. "This information may be useful in advocating weight control in the young and lean who are likely unaware of the insidious nature of weight gain," says Williams.
Obesity is a leading cause of preventable death in the United States, second only to smoking. The proportion of adults who are obese rose in the U.S. from 15 percent in 1980 to 33 percent in the early part of this decade. It is expected to reach 50 percent by 2030 according to a 2008 Johns Hopkins study. Among the explanations proposed are consumption of energy-dense foods, larger food-portion sizes, too little activity, and even widespread availability of air conditioning. The obesity epidemic has alarmed U.S. health officials and become a cause for First Lady Michelle Obama, who inaugurated her "Let’s Move" fitness campaign in April 2009.
While the causes of this rapid increase in obesity are continually debated, there is general agreement that weight gain and obesity are associated with a number of major risk factors, including a sedentary lifestyle, low-educational attainment, family history of obesity, and poor dietary choices.
In an earlier study, Williams first detected statistical evidence that the risk of obesity posed by a sedentary lifestyle was more pronounced among people who were already overweight. The latest study builds on that finding, and revealed striking evidence that obesity magnifies those three other risk factors. These effects emerged when Williams applied a statistical technique known as quantile regression, which divides people into groups based on how fat or lean they are, and analyzes the relationship between Body Mass Index (BMI) and risk factors of the different groups. BMI is a measure of body fat calculated by a formula that compares weight and height.
Differences in susceptibility to risk emerged clearly when BMI’s of the heaviest 10 percent (90th percentile) and leanest 10 percent (10th percentile) were matched to various risk factors. For example, when the effect of low educational attainment on BMI was considered, it was at least three times stronger among the heaviest 10 percent of women in the study compared to the leanest 10 percent. Among men, the difference was twice as strong in the heaviest group.
Similarly, among women the adverse effect of a diet high in meat and low in fruit was at least four times greater for the heaviest group; among men it was at least twice as strong for the heaviest group. Among both men and women, the effects of a family history of obesity were twice as strong for the heaviest groups.
Williams’ statistical analysis shows a pattern of risk factor amplification. "The three major risk factor for obesity -- poor dietary choices, low educational attainment, and a family history of obesity -- all had relationships to obesity that were strongest in men and women who were heaviest, least in those who were leanest, and intermediate in those of average weight," he notes.
While the statistics reveal a pattern of obesity compounding itself, they show only an association, not a cause. Williams says that further research is warranted to find a biomedical process responsible for this phenomenon.
Evidence to support this notion of a vicious circle of obesity is found in William’s analysis of data collected from two large cohorts of Americans who have provided a rich source of information about their diet, exercise, health, and demographic background: The National Runners’ Health Study, which began in 1991, and the National Walker’ Health Study, which began in 1996. Together, these studies included 159,000 participants. From those two studies, Williams examined subsets totaling nearly 15,000 men and 26,000 women and began to tease out of the mountain of statistics data strongly suggesting that obesity has a way of building upon itself.
Williams’ paper, "Evidence that obesity risk factor potencies are weight dependent, a phenomenon that may explain accelerated weight gain in western societies," is published in the Nov 23, 2011 edition of PLoS One (http://dx.plos.org/10.1371/journal.pone.0027657), a peer-reviewed, open-source scientific journal.
–Written by Sabin Russell