Editor's note: This article is the second of two parts. You can read Part I here.
A new study by Youfa Wang of John Hopkins University and Tim Lobstein of the International Obesity Task Force published in the International Journal of Pediatric Obesity, claims that half the children in North and South America and 38 percent of the children in Europe will be overweight or obese by 2010 if trends continue.
This has important implications for health, the researchers claim, because "obesity is the second leading cause of preventable disease and death, surpassed only by smoking" in the United States. And they also argue: "Obesity in early life is of particular concern due to its associated health consequences. ... Childhood obesity also confers long-term effects on mortality and morbidity."
Here's the problem: None of their claims is true.
For all the scares about a rising tide of child obesity, studies show that there is no epidemic. Trends for overweight and obesity have remained flat in recent years, at least in the leading edge countries, the United States, United Kingdom and Canada.
And the claim about overweight and obesity being the second leading cause of death was soundly refuted by the Centers for Disease Control almost a year ago. Katherine Flegal et al. reported net annual deaths from overweight and obesity at 25,814, not 400,000 as previously reported. Tim Gronniger of the Congressional Budget Office, in a recent American Journal of Public Health study, noted in the clearest language yet about the fat=early-death claim:
"Normal weight individuals of both genders did not appear to be relatively more long-lived than mildly obese individuals (BMI's of 30-35), whereas overweight people (BMI's of 25-30) appear healthiest of all."
The claim that fat children become fat adults has little empirical support. A review of literature dating from 1993 by M.K. Serdula et al, "Do Obese Children Become Obese Adults," in Preventive Medicine reviewed 17 different studies that followed various cohorts of children from childhood through adolescence to adulthood. These studies found was that most children become thinner as they get older, not fatter. According to the authors, 75 percent of children two and younger, 70 percent of pre-schoolers and 50-60 percent of school age children who are overweight or obese lose their extra weight by the time they become adults. At most, according to the study, from 5 percent to 20 percent of obese adults were obese children.
A study just published in the American Journal of Clinical Nutrition by Ulf Ekelund et al. looked at the links between obesity in childhood and later life. It found rapid weight gain in infancy and early childhood led to larger adolescents, but reported nothing about the crucial question of adult weight.
An earlier study in The Journals of Gerontology by Kenneth F. Ferraro et al., "The Life Course of Severe Obesity: Does Childhood Overweight Matter?" found that only morbidly obese children -- that is children with BMI's greater than 35 -- were at risk for adult obesity. The same study also found, though, that being overweight as a child resulted in LOWER adult mortality for women, and overweight children who were not morbidly obese did not have increased risks for mortality -- findings that contradict the claim that overweight and obese children are at risk for shorter adult lives.
The most definitive refutation of the fat-child=fat-at-risk-adult claim comes in the Newcastle Thousand Families Study from the United Kingdom. The study has followed a 1947 birth cohort from one thousand families in the northeastern English city of Newcastle since 1954. In an analysis of the effects of childhood obesity on adult obesity and health, "Implications of childhood obesity for adult health," British Medical Journal, Charlotte Wright clinically reexamined 412 of the original children when they reached age 50. Contrary to the claims that fat children become fat adults, her examinations found that there "was little tracking from childhood overweight to adulthood obesity." Indeed, when looking at obese adults, it was found that almost 80 percent of obese 36-year-olds, for example, became obese as adults not as children or adolescents.
As Wright noted in response to a letter claiming a large association between childhood and adult obesity,
"...it has been clearly demonstrated in many studies, as well as our own, that most obese adults were not fat children, but this is not generally known and is rarely mentioned when childhood obesity is discussed."
She went on:
"We found no evidence that being a thin child is of long term health benefit. We thus argue that efforts to turn the tide of adult obesity will be misdirected it they are directed primarily at turning plump children into thin children. The target should be those who are truly at risk: inactive, overeating adults."
Wright's conclusions are also found in a recent study in Pediatrics, "Screening and Interventions for Childhood Overweight" by E.P. Whitlock et al., which reported that the best current evidence indicates that a "substantial proportion of children under age 12 or 13, even with BMIs of >95th percentile [obese], will not develop adult obesity."
But even though most fat children do not become fat adults, some do. Why is this? According to James and the other obesity crusaders it is because of the pernicious influence of the food industry. Fat children are fat children and go on to become fat adults because of what they eat, and what they eat is determined by the Big Food industry.
The evidence, though, points at a very different culprit -- not the food industry but the children's parents, more specifically their mothers.
A 2001 study in BMJ by Tessa Parsons et al. looking at a 1958 birth cohort at ages 7, 11, 16, 23 and 33 found that it was the maternal weight (BMI) that explains the association between birth weight and subsequent adult weight. A recent Swedish study by M. Bonsestam et al. in Acta Paediatrica that looked at obesity and overweight in children in relation to parental BMIs also found a significant correlation between parental and child BMIs. So, too, did the Avon longitudinal study of parents and children from England, which found a high correlation of later obesity with infant size and body mass -- hardly something to be blamed on fast food restaurants or soda pop.
Indeed, Janis Baird et al. in a 2005 BMJ review of studies on later obesity and infant size -- "Being big or growing fast: systematic review of size and growth in infancy and later obesity" -- found that risk of subsequent obesity was strongly linked to infants with high BMI's. And a 2004 American study, "Predicting Preschooler Obesity at Birth" by Dr. Robert Whitaker in Birth Pediatrics, found that "among low-income children, maternal obesity in early pregnancy more than doubles the risk of obesity at 2 to four years of age."
Why is this evidence linking parental weight, particularly mother's prenatal weight, with child obesity largely ignored in favor of the claim that it is children's diets that make them fat?
That may be the most obvious yet often overlooked part of this story. While stories about supposedly epidemic increases in the numbers of overweight and obese adults may generate headlines, it is the epidemic of childhood obesity that grabs the most attention of everyone from the soccer mom to the policy wonk.
Threats to children assume an immediate and often uncritical priority: they generate moral panics much more reliably than adult issues. By focusing on the dangers of obesity for children, the obesity crusaders are guaranteed not only far more sympathetic and uncritical attention from the media, but also from parents and policy makers. Fat kids are important, because their plight can generate support for more research dollars, more government money, diet aids and more draconian policy interventions that would never be tolerated if the issue were simply fat adults.
"Just do it for the kids" has a powerful emotional logic that can easily short-circuit logic and preclude a rational discussion of the facts, which is just what the purveyors of fears and fictions desire.
John Luik is writing a book about health policy.