Friday » September 12 » 2003

When rich and poor kids eat the same diet, poor ones get fatter

Brad Evenson
National Post

 Children from poorer families tended to be most overweight, researchers
say. But don't blame the parents because how they brought them up seemed to
make no difference at all.

Liz Goodman is part of a growing group of researchers who believe growing
up poor, or feeling poor, makes you fat.

"Over the past 20 years, economic and social inequalitites have been
rising," says Dr. Goodman, an obesity researcher at Brandeis University in
Waltham, Mass.

"And it's interesting that there's this burgeoning epidemic of obesity at
the same time."

As another scientist puts it, "Poverty really does get under your skin."

In Canada, kids from poor families are twice as likely to be obese as rich
kids. A study published in August in the International Journal of Obesity
found 6.4% of children in the wealthiest quarter of the Canadian population
were obese, compared with 12.8% of those in the poorest quarter. The
heaviest children live in single-parent homes, with 46% either overweight
or obese.

It's easy to blame obesity on poor diet and lack of exercise. But this is
overly simplistic, like blaming high unemployment on the number of people
watching afternoon television. It doesn't explain underlying causes.

Experts say the deeper roots of the obesity problem lie at the crossroads
between social status and biology. Generally speaking, even if rich kids
and poor kids eat exactly the same diet -- from Big Macs and fries to tofu
and granola -- the poor kids get fatter.

"I believe that there's much more biology to this than what we've been
willing to recognize in the past," says Dr. Goodman.

The centre of this poverty-obesity link is a hormonal pathway known as the
HPA axis. This is a loop connecting the hypothalamus, a jellybean-size part
of the brain that governs appetite, and the pituitary and adrenal glands,
which secrete a variety of hormones, including the stress hormone cortisol.

Cortisol helps the liver convert fat into the lightning bursts of energy
the body needs to escape danger, a vital function. But it also signals the
body to accumulate mounds of fat in the abdomen, building the "apple" shape
that is so hazardous to health.

"When you have too much cortisol, you have Cushing's disease, which is an
illness that causes central fat deposition," says Dr. Goodman.

Once this fat builds up, it spews a toxic array of chemical signals back to
the brain and into the body. "It's a vicious cycle," she says.

Research shows children raised in low socioeconomic settings produce
greater amounts of cortisol, a stress hormone.

In a 2001 study, researchers from McGill University measured the hormone
levels of 300 children from poor to wealthy families. They found three
times as much cortisol in low-income kids compared with rich kids.

"The differences are especially big in elementary school," says lead
researcher Sonia Lupien.

Not only does increased cortisol lead directly to a fat waistline, Dr.
Lupien points out it can also trigger depression, which opens a surprising
new chapter in obesity research.

The conventional thinking goes that kids who are fat get depressed about
their plight. But in a 2002 study of 10,000 U.S. teens, published in the
journal Pediatrics, Dr. Goodman and her colleagues discovered just the
opposite.

"We looked at people who were overweight or obese at the beginning and
whether or not that increased depressive symptoms over time. And it
didn't," she says.

"But if you were depressed [but not overweight] at the beginning, you were
more likely to become overweight. In fact, there was about a twofold
increase in risk of becoming obese."

In other words, skinny depressed kids get fat, and fat depressed kids get
even fatter, which explains why some doctors have successfully treated some
obesity patients with the anti-depressant Prozac.

Poverty can lead to obesity in other ways than stress. Many low-income
parents cannot afford to enroll their children in organized sports. They
may also choose less healthy foods at the supermarket and use TV or video
games as babysitters, says Mark Tremblay, senior scientific advisor for
health measurement at Statistics Canada.

This is unfortunate, because kids with elevated cortisol need the most
physical activity to lower it.

"The child from the poorer background with the altered hormone profile
would benefit to a greater extent from exercise, because that's what
exercise does," says Dr. Tremblay. "It helps get cortisol and other
hormones under control. It blunts future stress responses to that. So the
lower [socioeconomic status] child would have more to gain."

Dr. Tremblay does not believe poverty leads inevitably to a high body mass
index -- it's not destiny, he says. Lack of exercise, too much TV and video
games are more potent factors. But he agrees biology plays a big role in
the obesity of the underclass.

"Clearly, it's at the cellular level that the calories are used up and the
energy liberated," he says. "So the biology has a huge impact."

While many people blame mothers and fathers for the obesity of their
children, research shows parenting styles -- strict, abusive, lax or
indifferent -- make little difference. A Duke University study published
this year in the journal Pediatrics tracked nearly 1,000 white North
Carolina children aged nine to 16 for a period of eight years. Young boys
-- but not girls -- seemed especially vulnerable to dual cases of
depression with obesity. And researchers found kids from poorer families
tended to be most overweight. But how their parents brought them up, strict
or lenient, seemed to make no difference.

"My biggest surprise was that ... almost none of the [parenting styles]
were significant in predicting obesity," says lead researcher Susan
Mustillo, of Duke University Medical Center.

Anyone doubting the links between stress, poverty and fat need only look at
Eastern Europe after the collapse of the Soviety Union.

After the reunification of Germany in 1990, the body mass indexes of East
German children and young adults rose sharply compared with those in West
Germany. German public health officials say class inequalities rose after
reunification, leading to poverty and unemployment, which had powerful
health effects.

An even more stark example of the connections between chronic stress,
social dislocation, abnormalities of the HPA axis and cortisol secretion
comes from a 1998 study done in Sweden and Lithuania. Researchers from
Linköping University compared 150 randomly sampled men, aged 50, from the
cities of Vilnius and Linköping, to assess their risks of heart disease. At
the time, Lithuania was struggling to adjust to a Western style economy.

"Compared to Linköping men, Vilnius men had unfavourable psychosocial
coronary risk factors," said lead researcher Margareta Kristenson.

"They reported more job strain, more social isolation, less effective
coping strategies, lower self-esteem, more depression and vital
exhaustion."

Perhaps the most remarkable finding was the stress response. When the
researchers subjected the Swedish men to a stress test, the subjects'
cortisol levels jumped sharply. But the levels in the Lithuanians barely
budged -- they were already high. While levels soon dropped to normal in
the Swedes, they ebbed much more slowly in the Vilnius men.

"This attenuated stress response has earlier been shown in states of
chronic stress," reported Dr. Kristenson.

Health researchers say Canada is starting to look more like Lithuania than
Sweden these days. They blame the shift to conservative governments.

"In Ontario, the risk of diabetes is four times higher in low-income women
than high income," says Dennis Raphael, an associate professor in the
School of Health Policy and Management at York University in Toronto.

Diabetes mellitus, a common complication of obesity, is twice as common
among middle-aged Canadians with household incomes less than $30,000 than
those living in households with incomes of $60,000 or higher. And rates
have increased sharply since the mid-1980s. By 2010, an estimated four
million Canadians will have diabetes.

Dr. Raphael says the shift to more conservative governments around the
world is a big factor.

"If you're serious about population health, and if you're serious about
heart disease and diabetes, then you don't want to create the kind of
policy environments we've been creating in Ontario and in Canada," he says.

"You don't want to increase housing insecurity, you don't want to increase
income insecurity, you don't want to increase food insecurity, and you
don't want to go out of your way to make life difficult for people."

Part six of a six-part series.; [log in to unmask]

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