Prevalence of overweight and obesity

The prevalence of obesity has increased sharply from the early 1980s, for both adults and children, after holding fairly stable during the 1960s and 1970s. Then they gained considerable weight, particularly at the upper end. In other words, heavier men and women became heavier.

Solid evidence for the increase comes from the National Health and Nutrition Examination Studies (NHANES), the nation’s most comprehensive look at our health and nutrition. In this series of multiyear studies, beginning in the mid 1960s, large, representative samples of Americans are interviewed, weighed, measured and clinically tested in mobile clinical centers.

The same increases are seen worldwide. There is every reason to expect that obesity and its associated health risks (perhaps especially related to sedentary lifestyles) will extend globally into the future as developing countries modernize.

Some of the highest rates of obesity in the world are found in Polynesian populations, as people move from rural areas to the cities, changing both their activity levels and nutrition practices. About 77 percent of women in American Samoa and 63 percent of native Hawaiian women have a BMI of 27.3 or more. One study in Hawaii found an average BMI of 31 for both men and women.

Obesity is less common in Africa and Asia. However, it is more prevalent in urban areas and growing as people move from their rural villages to the cities. In Asian cities, there is growing concern for escalating rates of both obesity and eating disorders. It should be noted that for most countries statistics are still incomplete, and not based on representative samples.

The American woman at the median, or midpoint, is 5-foot-4 ½ inches tall and weighs 144 pounds. This is an increase of a half-inch taller and six pounds heavier since 1980. She has a body mass index (BMI) of 25, up from 24. (The average woman is a little heavier, but since this statistic can be a distortion it is used less often.) The median man is 5-foot-10, weighs 176 pounds, and has a BMI of 26, an inch taller and six pounds heavier than in 1980.
(Excerpted from Women Afraid to Eat: Breaking Free in Today’s Weight-Obsessed World.)

Obesity increase leveling off

After a quarter century of increases, weight gain has leveled off in the past few years, according to the latest announcement from the NHANES surveys, conducted by CDC’s National Center for Health Statistics.

The 2005-2006 study reported by CDC in November 2007 shows that, while the obesity rate appears to be up somewhat, the figures are not statistically different from 2003-2004.

The new figures suggest more than one-third of U.S. adults – over 72 million people, 34 percent of adults age 20-74 – were obese in 2005-2006. This includes 33.3 percent of men and 35.3 percent of women. This is a change, though not statistically significant, from 2003-2004 when 32.9 percent of adults were found to be obese including 31.1 percent of men and 33.2 percent of women.
Adults age 40-59 had the highest obesity prevalence compared with other age groups, with about 40 percent of men and 41 percent of women in this age group being obese. Younger and older ages had lower rates. There were large race-ethnic disparities in obesity prevalence, especially among non-Hispanic black women and Mexican-American women.

The two surveys show increases in overweight among children and teens. For children age 2–5 years, the prevalence of overweight increased from 5 percent to 13.9 percent; for those age 6–11 years, prevalence increased from 6.5 percent to 18.8 percent; and for those age 12–19 years, prevalence increased from 5 percent to 17.4 percent. (CDC News Release Nov. 2007)

Note: CDC no longer includes the “overweight” category in its news releases after the agency’s own research by Flegal found this to be the level associated with the lowest mortality rates. Neither does it include categories other than obese, even though the Flegal research found higher risks to be focused at the upper end of that category, with higher risks at the “normal” level, and much higher risks in the “underweight” level. Thus, unfortunately, such official reports fail to provide a true picture of current weight-related risks in the U.S.

See Controversies – Flegal

Child prevalence

Overweight rates for children, too, have increased steadily since the 1960s and 1970s, when they had remained fairly stable. At that time, when the standards were set (using a bell-shaped normal distribution system), 5 percent of children were at or above the 95th percentile and considered overweight.

Since then there has been a dramatic increase in the percentage of overweight children.
A comparison of statistics over these years illustrates the increasing prevalence of overweight for children and adolescents aged six to nineteen:

Overweight rates doubled in the 1980s, and have now more than tripled. The studies also find that not only are more American youngsters overweight today, but they are more severely overweight than ever before.

A similar pattern of increasing weight for children can be seen worldwide. Western European countries have generally had lower overweight rates than the U.S. In Germany a recent survey found that in the past twenty years rates rose from 5 percent to 8 percent for boys and from 5 percent to 10 percent for girls.

Definition of overweight and obesity

The following weight categories for adults were set in 1998.

Body mass index (BMI) is calculated from a person’s weight and height and, although it does not measure body fat, is often used as a proxy for body fatness. For adults, obesity is defined as a BMI of 30 or greater, overweight as a BMI of 25 - 29.9. Normal weight or “healthy weight,” as it is sometimes called, is defined as a BMI of 18.5 to 24.9 or under 25. These categories remain controversial: many experts say they are set too low, because they assume there are health risks above a BMI of 25, which is not supported by research.

See Controversies – Flegal

CDC growth charts are used to plot percentile rankings for children. The charts are based on BMI -for-age and differ for girls and boys. For children the terms at risk of overweight and overweight are used (comparable to overweight and obese in adults). Children are not defined as “obese” in efforts to avoid the stigma and its potential for contributing to adverse effects such as disturbed eating, dangerous weight loss efforts, nutrient deficiencies, body hatred, social discrimination and size harassment.

Causes of obesity

Obesity and overweight are complex conditions that baffle scientists at nearly every turn. The fact is, there is much we don’t know about excessive fat gain — or what to do about it.

Where does it start, and why are we seeing such sudden increases? Does it begin in early childhood through excessive fat cell development, or even in the womb? Is it most likely triggered at high-risk points during a child’s development? How powerful are genetic factors? And if heredity is the important determining factor – why are we seeing these steep increases?

Clearly, much has a genetic basis. One easy answer for the rise is that our steepest population increases have come in the very groups most vulnerable to obesity. A higher percent of our children today than a generation ago comes from groups that have disproportionately high rates of obesity. Children most vulnerable to excessive weight gain are most likely to come from minority groups, low-income families, or those with less education. About 20 percent of African American and Hispanic children are overweight.

Thus, “thrifty genes” may share the blame, along with other factors. Yet increases have come across the board, in every ethnic, racial and economic group, for boys and girls of all ages.

Another logical and likely explanation is that children today are much more sedentary than children have ever been before. Again, this is part of the equation.

It once was believed that obesity was mainly an overeating problem – simply too many calories. This is less certain today. Or maybe, it’s the wrong foods, too high in fat and sugars, and too low in fiber. But again, the answers are unclear. Over-consumption of rich foods may well be part of the problem, but perhaps only when combined with sedentary living.

Other factors in the equation are even more complex. [More than 20 probable causes affecting excess weight gain – from bigger babies to smoking cessation, from inflammation to medications – are discussed in the book Underage and Overweight, Ch. 3: Nature vs Nurture, p 33-55.]

(Excerpted from Underage and Overweight: Our Childhood Obesity Crisis – What Every Family Needs to Know)

Keeping a sound perspective

Though statistics on the increases in overweight for children are staggering, it is important to consider them in context – not all kids are gaining weight. More than 80 percent are not overweight.

A few decades ago there was perhaps one large child in a class of 20 – now there may be two or three. In areas with low income or high minority populations perhaps half the students will be overweight.

Nonetheless, if you go to a school and look around you’ll see that most children and teenagers are quite slender. They are representative of that other 80-some percent of children, whose body types range from tall and rail thin to short with soft curves, and everything in between. Among them are many painfully thin girls are, poorly nourished.
You will see the signs of children moving through the natural stages of puberty, rapid growth, and emerging maturity. The weight of most children in the various age groups has remained steady over the past three decades. And many classified as overweight are well-muscled athletes or simply big kids.

So it’s important that obesity concerns not dominate others, such as the need for growing children to be fully nourished, moderately active and live in a nurturing environment. In the big picture it is the child’s total wellness that counts. Physical, emotional and social health are all part of the bigger picture. Despite concerns over the possible risks of obesity, it is a mistake to exaggerate those risks.

(Excerpted from Underage and Overweight: Our Childhood Obesity Crisis – What Every Family Needs to Know)