Junkfood Science: <i>Junkfood Science Special:</i> New Age Numerology — Why kids are little Tyrannosaurus rexes

January 23, 2007

Junkfood Science Special: New Age Numerology — Why kids are little Tyrannosaurus rexes

Parents have a tough job. They want what’s best for their children but they’re being bombarded from every direction with frightening information indicating that their children are in danger. One of the biggest worries for any parent is whether their child is growing normally and is healthy.

Today, they hear so many conflicting numbers and definitions for “overweight,” “at risk for overweight,” “obese,” “body mass index,” and percentiles on a growth curve. But most parents would probably be surprised to learn just how arbitrary and controversial these definitions are and the level of special interests and politics behind them.

Growth charts and growing kids

Decades of American pediatricians have used the growth charts developed in 1977 to help them track each child’s growth pattern. The original charts had been created by the National Center for Health Statistics at the U.S. Centers for Disease Control and Prevention by plotting on a graph the head circumferences, weights and heights of a sample of American children back then. Smooth curves were then drawn using statistics to represent the ranges found among those children at different ages, with different percentiles marked. Growth charts are one tool doctors have used to help ensure each child was growing well. Special attention has traditionally been given to children who “fall off” their growth curve — that means a child drops below the percentile range normal for them which could indicate a medical problem or that the child isn’t getting enough calories, fats and nutrition necessary for their brains and bodies to develop well.

Growth charts might seem pretty cut and dry, but they’re much more complicated. Every single child is uniquely different. When a pediatrician finds a child at higher or lower percentiles on the growth chart, they first look at their parents and families. All children take after their families, with some being short and stout, others tall and thin, and everything in between. If a little one was premature or small for their age at birth, they may also fall lower on the curve for a few years before catching up. Each child also grows at his/her own rate and manner. And kids don’t grow in nice even lines like the charts, either. They grow in spurts, some get taller first and then fill out, while others plump up first and then sprout up in height. Researchers at the University of Manchester reported in the Archives of Disease in Childhood that prepubescent children in their research had experienced 3 to 6 unpredictable growth spurts, lasting 13 to 155 days, with stable periods of 8 to 52 days in between. They also found growth was seasonal and slowed over the winter and spurted in the spring! Boys grow at different rates than girls and they all enter puberty at different ages. In addition to genetics, good nutrition, health and socioeconomic status affects the onset of puberty. Every child at a given age is at a different level of maturity which can significantly affect where they fall on those growth curves. Children with family genes for being fatter also tend to be taller, mature earlier and have advanced bone ages and fall higher on the curve compared to genetically smaller children. The point is, it's all normal!

What matters is whether each child is “tracking” on their individual growth curve in a way that is normal for them. Traditionally, wherever a child fell on the curve, if he/she was growing and generally staying in the range normal for him/her and otherwise healthy, pediatricians would be unconcerned. Today, with the growing panic over obesity, some have directed their attention to children in the upper percentiles. But as you recognize now by understanding how children normally grow, overreacting to a child who plumps up could compromise their normal growth. Researchers at the CDC Pediatric Nutrition Surveillance System followed nearly 11,000 children through preschool years, for example, and found a high rate of shifting several major percentiles up and down on the growth curve as they grew. In a June 2004 issue Pediatrics, they cautioned pediatricians that such shifts in childhood are a “normal phenomena that affects large numbers of children” and a period of “watchful waiting” is prudent before raising concerns about obesity.

But puberty is where growth spurts can exceed all expectations. Teenagers are a lot like teenage tyrannosaurus rexes. As paleobiologist, Gregory M. Erickson, at Florida State University in Tallahassee found, upon examing the remains of four tyrannosaur species, during their adolescence growth spurt these dinosaurs put on as much as half their adult weight in a mere 4 years! Human teens, eating their parents out of house and home aren’t much different. :)

Girls begin puberty at 8 to 15 years of age, well before boys, and it is a period of rapid fat gain for them. It’s normal for girls to gain 20 or more pounds in one year as their bodies prepare for childbearing. “At puberty, it is natural and healthy for girls to add up to 20 percent of their body weight in fat,” said Kathy Kater, LICSW, a body image and eating disorder specialist in St. Paul, Minnesota and author of Real Kids Come in All Sizes (2004). When girls and their parents don’t expect or understand this normal change, puberty is also when mistaken concerns about “getting fat” are especially prevalent. Even among some health professionals who should know better.

The dividing line between acceptable and “too” fat

How are the cut-offs on the growth curves labeling children as “too” fat or “too” thin chosen? Surprisingly arbitrarily. A 1999 review of 26 countries, published in the American Journal of Clinical Nutrition, looked at the methods, reference information and cutoff points used and found all were considerably different. There is even significant variations in the measurements among kids in different countries and ethnicities.

In the U.S., using data on American children, weights above the 95th percentile have traditionally been labeled “overweight,” and weights in the 85th-95th percentile termed “at risk for overweight.” [Because of normal fluctuations during growth and development and the natural variations among children, the medical community, including the CDC, has long resisted any attempts to label these children as “overweight.” Never mind that there is no sound data to support the idea that these children actually go on to become fat.]

But other countries use different data and cutoffs and those are “intrinsically no more valid than the 90th, 92st, 97th or 98th centile,” said researchers inside the CDC in the May 6, 2000 issue of the British Medical Journal. “Regardless, the cut off point can still be criticized as arbitrary.”

Calling a child “overweight” simply because he/she is at the top 5% of children, hence insuring 5% of children will always be labeled as “overweight,” has been criticized as irrational. And creating the illusion that children in the 85th-95th percentiles are somehow at risk has no basis in fact. The growth curves have traditionally been used on an individual basis, not as a way to compare children. These children “are not necessarily ‘overfat’ or ‘sick’ or at risk of imminent illness, and they should not be labeled as such,” said Dr. Jennifer O’Dea, MPH, Ph.D., an internationally-known childhood obesity researcher, and nutrition and eating disorder specialist at the University of Sydney, Australia. “Giving children this ‘fat, sick’ label is inaccurate and unhelpful.”

Changes afoot

But the growth charts underwent a significant change in 2000 which has made them even more controversial. The new charts, issued by the CDC in May 2000, were based on BMIs, rather than weights and heights. They were announced by Health and Human Services Secretary Donna E. Shalala and Surgeon General David Satcher at a press conference and became part of “a national action plan to address weight problems and obesity.” Secretary Shalala told audiences: “The BMI is an early warning signal that is helpful as early as age 2. This means that parents have an opportunity to change their children's eating habits before a weight problem ever develops.”

What didn’t make the news and few parents may know is that the new BMI-based growth charts meant children’s percentile on the growth curves changed. With the new charts, nearly two-thirds of children were suddenly at higher percentiles, with greater discrepancies among shorter children. And children were more likely to be classified as above the 85th percentile, according to Katherine Flegal and colleagues inside the CDC’s National Center for Health Statistics.

As was discussed in this post and this post, BMI measurements in children (and adults) are not accurate measures of fitness, behaviors, health or future health outcomes. But our society gives a lot of power to what is believed a number says about us or our children. I can think of no better word than numerology to describe the soundness of today’s obsession with divining meaning from most health indices.

Numerology: “The study of the magical meanings of numbers and of their supposed influence on human life. It is a purported calculative means of obtaining information about one's personality, capabilities and future.” — Jack Raso, M.S., R.D., Dictionary of Metaphysical Healthcare (1997)

There are several important points that parents may find helpful when they are given their child’s BMI. BMI numbers in children are very different from adult numbers. BMIs are lower in children and they change with a child’s age, so it is normal for their BMIs to increase as they grow. Body compositions and disease risks are also radically different between adults and children, said Dr. John J. Reilly, Department of Human Nutrition, University of Glasgow, Scotland. The adult cutoffs of 25 and 30 to define “obese” and “overweight” were based on adult illnesses, not children’s, but even they were arbitrary and “chosen primarily for convenience.” The adult cut-offs of 25 and 30, said Flegal and colleagues, were simply “convenient round numbers.”

Deducing from adult values to equivalent BMI percentiles in children is inappropriate, said Dr. Reilly. After outlining the weaknesses of adult BMIs in a 2002 issue of Obesity Research, he concluded:

[W]e should not extrapolate what are essentially limited adult definitions into pediatric use without good evidence that this is practical, safe, and offers an improvement over existing pediatric obesity definitions.

If these failures weren’t bad enough, children today are maturing earlier and are taller and larger than children were 40 years ago when the charts were developed. So instead of 5% of children falling in the top 5th percentile, today, about 15% of children do. And another 15% fall in the 85th-95th percentile.

But it even goes beyond the data being used and the cutoffs being chosen. There has been another growing movement over recent years — spearheaded by weight loss interests using claims of an “obesity epidemic” — to change the labels applied to the various growth chart percentiles.

In order to create a perception of an epidemic of childhood obesity, they need “obese” children.

So, rather than use the term “overweight” to describe children in the top 5th percentile on the growth curves, they are moving to label them “obese.” And children in the 85th-95th percentiles, previously “at risk,” are now being called “overweight.”

Those same interests are increasingly going a step further. They are describing the epidemic by piling onto their newly-labeled “obese” children, the “overweight” children, as well. It serves to effectively double the numbers of children that can now be considered “too” fat.

“The figure of 30% often reported in the media is an overstatement that ought to be qualified every time it is used, since about two-thirds of those are mislabelled as overweight. They are simply bigger and possibly fatter than their peers,” said Dr. O’Dea.

There is a lot more to this story that the public hasn’t heard and the truth behind claims of an epidemic of childhood obesity. Stay tuned for more on the creation of this epidemic.

© 2007 Sandy Szwarc

Bookmark and Share