Obesity, Type 2 Diabetes, and Physical Activity
What's the Connection?
by Richard M. Weil, M.Ed., C.D.E.
It's no coincidence that the rate of Type 2 diabetes is
rising as rapidly as the rate of obesity in the United States. The two
are strongly related: The heavier people are, the more likely they are
to develop diabetes. So strong is the connection between obesity and diabetes
that a new word, "diabesity," has been coined by the medical community.
(The first diabesity conference was held in Virginia in March 2001.)
It's also no coincidence that Type 2 diabetes and obesity
are on the rise at a time when physical inactivity is commonplace. Currently,
more than 70% of the U.S. population is physically inactive. People who
are physically inactive tend to be heavier than people who are active,
and they tend to have more diabetes too.
While the rises in obesity and Type 2 diabetes show no
signs of slowing any time soon, research suggests that something can be
done to increase the number of people who are physically active and to
decrease the number who develop obesity and Type 2 diabetes. This article
offers suggestions to help individuals make informed decisions about losing
weight and becoming more physically active.
In 1960, 43% of American adults (ages 20-80) were overweight
or obese. Today, that number is 55%, or 97 million adults. If the increase
in overweight and obesity continues at the current rate, by the year 2020,
61%, or 103 million adults, will be overweight or obese.
Overweight refers to an excess of body weight compared
with standards set by the National Institutes of Health and the National
Heart, Lung, and Blood Institute (NHLBI). The excess weight may come from
muscle, bone, fat, or body water.
Obesity refers specifically to having an abnormally high
proportion of body fat. One can be overweight without being obese, but
many people who are overweight are also obese. Of the 97 million adults
in the United States who are overweight or obese, almost 40 million are
obese.
The most up-to-date method of assessing whether a person
is overweight or obese is to calculate his body-mass index (BMI). This is done by dividing body weight (in kilograms) by height (in meters) squared. (See the Adobe Acrobat PDF file "Body-Mass Index" for determining your BMI based on your weight in pounds and height in inches.)
According to the
NHLBI, normal weight is defined as a BMI less than 25 kg/m2, overweight
as a BMI of 25-29.9 kg/m2, and obesity as a BMI of greater than or equal
to 30 kg/m2.
Although BMI is simple and inexpensive to calculate and
applies to both men and women (but not to children), it has some drawbacks.
One problem is that it may misclassify individuals who are muscular. For
example, a lean, muscular football player who is 5'11" and weighs 225
pounds has a BMI of 31.5 kg/m2. By definition, that puts him in the obese
category, but he obviously isn't obese.
BMI is best used to help estimate your relative, weight-related
risk of disease compared to normal weight. But since some people can be
healthy even if their BMI is high, don't make assumptions about your health
risk based solely on your BMI. Check with your doctor for other indicators
of health risks such as high blood pressure, high blood sugar, low HDL
cholesterol, and high total cholesterol, triglycerides, and LDL cholesterol.
If your BMI is 25-29.9 kg/m2 and you don't have any risk factors, you
probably don't need to lose any weight for health reasons.
The health risks, or comorbidities, of being overweight or obese
include Type 2 diabetes, gallbladder disease, coronary heart disease,
abnormal blood lipids, hypertension, sleep apnea, osteoarthritis, stroke,
respiratory problems, vascular diseases, and uterine, breast, kidney,
gallbladder, prostate, endometrial, and colon cancer.
It has recently been estimated that 300,000 deaths per
year can be attributed to obesity among American adults, making it the
second leading preventable cause of death in the United States after tobacco
use. The total costs of treatment and prevention of obesity exceed $99
billion per year, with approximately $51 billion spent on direct medical
costs such as drugs and hospitalizations.
Not all body fat is created equal, however. Fat tends
to collect in two primary areas of the body: the abdomen (creating the
"apple" shape more common in men), and the hips, buttocks, and thighs
(creating the "pear" shape more common in women). Although fat on the
lower extremities may be unsightly to some, it does not pose the same
health risks as abdominal fat.
Deep abdominal fat that surrounds the organs is called visceral fat and
is the fat most likely to cause the health risks of obesity, probably
because of its close proximity to the liver and other organs. Because
abdominal girth is a good predictor of visceral fat, circumference
measurements around the torso (at the level of the belly button) can be
used to assess abdominal fat. Abdominal girth of 40 inches or more for
men and 35 inches or more for women have been associated with higher levels
of insulin resistance, cardiovascular disease, cancer, diabetes, and other
conditions.
Obesity is a complex disease that involves the interaction
of genetics, physiology, metabolism, and lifestyle. While genetics play
an important part, the degree of impact varies from person to person.
Recent studies indicate that for some people, genetic factors may be 25%
responsible for an individual's body mass and body fat, while for others,
genetics may be 70% of the story.
Genes carry the biological code that determines everything
from the color of your eyes to the length of your toes. There are genes
for diseases as well. Scientists believe that there may be a cluster of
genes for obesity. If you are born with any of the genes for obesity,
you have a predisposition for the disease. But having a predisposition
for obesity doesn't mean you will definitely be obese. That depends on
many factors, perhaps the most important being your lifestyle. For example,
if you are sedentary, consume more calories than you expend, and have
a predisposition for obesity, the likelihood of becoming overweight or
obese is high. However, even if you have obesity genes, if you burn lots
of calories with regular physical activity, the genes may not express
themselves.
This idea is best exemplified in Native Americans, a population
that has a genetically high predisposition for diabetes (and perhaps for
obesity as well). When Native Americans live traditional hunter-gatherer
lifestyles, they stay slim and rarely develop diabetes. But when they
live sedentary lives and their diets include lots of fat, refined sugar,
and excess calories, they gain weight and develop diabetes and heart disease,
sometimes at alarming rates.
The same phenomenon has been observed among the Aborigines
of Australia. When they lived in the outback and hunted, fished, and gathered
plant foods, Aboriginal people had very low rates of diabetes. But when
they moved to cities, their collective rate of diabetes soared to three
times that of Australian Caucasians. Aborigines who have returned to traditional
lifestyles have seen their level of insulin resistance (a reliable indicator
of diabetes) decrease by 33%.
Genes may also affect the hormones that control satiety
(feeling full), appetite, metabolism, and fat distribution. We all know
someone who seems to eat as much as he likes and never gains a pound.
That's at least partly genetics, but there may be other factors at work
here, too. In one study, researchers fed a group of people 1,000 extra
calories per day for 80 days to get them to gain weight. The outcome was
that everyone gained a different amount of weight (the range was 9-32
pounds), even though they all consumed the same number of calories and
did similar levels of planned activity.
How is this possible? The researchers discovered that some people were
more active at rest than others. They actually fidgeted more, and this
accounted for a good deal of the variation in weight gain. The other factor
probably has to do with the presence or absence of so-called "thrifty"
genes. Thrifty genes are programmed to store fat efficiently—a vestige
of the Stone Age, when the body stored fat if food was plentiful in the
event that the next season might bring famine. Some of us, it seems, have
retained these ancient genes designed for storing fat efficiently. The
problem is that we live in an era and an area of the world where there
is almost always abundance and never famine, so our stored fat never gets
used.
In addition to there being plenty of food in our environment,
Western society has evolved to the point where physical activity is a
minimal part of our daily lives. Fewer jobs require physical exertion,
and we rely more on automobiles and public transportation than on our
legs to get around. In fact, over 75% of all trips in the United States
that were less than one mile were made by automobile in 1995.
Even if we wanted to walk more, there are plenty of reasons
not to. People tend to work long hours these days, and there seems to
be little time left to take care of ourselves and our families. When we
do have leisure time, there are many claims on our attention, such as
television and computers. The conveniences and temptations of modern life
may simply be too much competition for taking a walk to the store, riding
a bike, pushing a lawnmower, or washing the car by hand. But if our lifestyle
is contributing to the rising rates of obesity, then reversing the trend
almost certainly means changing our lifestyle. Are we willing to do that?
Although there is no cure for obesity, there are ways
to treat and manage it, including dietary changes, increased physical
activity, behavior therapy, and medication. Surgery is an option for the
most obese individuals (BMI greater than 40 kg/m2 or BMI greater than
35 kg/m2 with risk factors).
Most people can expect to lose 10% to 15% of their body
weight through diet, exercise, and behavior change techniques (although
some lose more), and a loss of even 10% of body weight will significantly
reduce weight-related health risks. However, 95% of people who lose weight
regain all of it within five years, and some gain back more than they
lost in the first place. How much weight is regained depends a lot on
diet and physical activity. Research shows that people who lose weight
but don't begin or continue a program of physical activity regain most
if not all of their weight in less than nine months. Those who are active
tend to maintain their weight loss.
Many scientists believe that obesity begins sometime in
the early stages of life, so working with children and their parents to
prevent obesity or treat it early makes a lot of sense, particularly since
it is so hard for adults to lose weight and keep it off. The limited amount
of research that has been done in this area shows encouraging results,
but the research is recent, and long-term results are not yet available.
In 1980, 5.8 million Americans had diabetes. Today, the
number of diagnosed cases is 10.3 million, a whopping increase of 77%.
By 2020, if the increase in diabetes continues at the current rate, 18.2
million Americans will have it.
The risk of developing diabetes increases as BMI increases.
A BMI over 22 kg/m2 is associated with an increased risk of diabetes,
and the risk jumps approximately 25% for every unit above 22 kg/m2. The
development of Type 2 diabetes is associated with weight gain after age
18, and it was recently estimated that 27% of new cases of diabetes were
attributable to weight gain in adulthood of 11 or more pounds. Among persons
who have been diagnosed with Type 2 diabetes, 67% have a BMI greater than
or equal to 27 kg/m2, and 46% have a BMI greater than or equal to 30 kg/m2.
Almost 800,000 new cases of diabetes are diagnosed each
year in the United States. The total yearly cost of treatment and prevention
exceeds $98 billion dollars, with approximately $44 billion dollars spent
on direct medical costs. A troubling feature of these numbers is that
while Type 2 diabetes was once considered a disease of adults 50 years
and older, approximately 25% of all new cases of Type 2 diabetes are diagnosed
in teenagers.
It is widely believed that this new health crisis in youth
is the result of inactivity, poor diet, obesity, and a genetic predisposition
for diabetes. While there is no generally accepted definition of obesity
as distinct from overweight in children and adolescents, the prevalence
of overweight is increasing for children and adolescents in the United
States, as is the level of physical inactivity.
We know that overweight people tend to get Type 2 diabetes
at a higher rate than lean people, but why? Evidence points toward a condition
called insulin resistance. On the walls of muscle cells are specialized
receptors that act as doors to let glucose pass from the bloodstream into
the cell, where it can be burned for fuel. The receptors are normally
locked, but insulin, a hormone produced by the pancreas, "unlocks" the
doors and allows glucose to come in. If the receptors are resistant to
insulin for any reason, glucose cannot enter the cell, and instead it
stays in the bloodstream. As a result, blood glucose levels rise, and
so does the risk of complications of diabetes.
The reasons for insulin resistance are not fully understood,
but the evidence strongly suggests that excess fat is a leading cause,
especially fat that accumulates in the abdomen. In simple terms, the fat
clogs up the receptors. When this occurs, not only does it lead to elevated
blood glucose levels and all the problems associated with that, but it
often leads to hyperinsulinemia (excess insulin in the blood), a common
condition in people who have Type 2 diabetes.
Hyperinsulinemia occurs when the pancreas, sensing that
blood glucose levels are rising (because of insulin resistance), produces
more and more insulin. While all this insulin may eventually lower blood
glucose levels to normal, it may also damage the inner linings of the
arteries and trigger other changes in body chemistry that encourage heart
disease. (Whether hyperinsulinemia directly damages blood vessels or is
simply a marker of underlying problems is a matter of controversy. There
is no doubt, however, that hyperinsulinemia is associated with atherosclerosis.)
Together, insulin resistance and hyperinsulinemia are
associated with a cluster of abnormalities collectively known as
syndrome
X. Those abnormalities include high blood pressure, heart disease, high
triglycerides, and decreased levels of HDL ("good") cholesterol. Syndrome
X has been shown to indicate a predisposition to diabetes and heart disease.
Treatment includes drugs to lower blood pressure and triglycerides and
to control blood sugar. But even the powerful drugs that are now available
cannot reverse diabetes or obesity or completely eliminate the health
risks that come with these conditions. That's why it's important to add
lifestyle measures, including increased physical activity, to the treatment
regimen.
Research shows that regular physical activity can improve
insulin sensitivity (or lower insulin resistance) by 20% to 30% by building
muscle and reducing body fat. It also helps lower blood sugar (exercise
has an insulinlike effect) and control weight. Research is also very clear
that it is almost impossible to maintain weight loss unless an individual
is physically active.
Physical activity increases muscle and bone strength,
increases the efficiency of the heart and lungs, reduces cholesterol levels,
reduces blood pressure, increases energy, improves quality of sleep, improves
appearance and posture, and reduces the risk of falling. It also increases
mental acuity, enhances psychological well-being, improves mood, and reduces
the symptoms of anxiety and depression (one study showed it may prevent
depression).
The current "official" recommendations regarding physical
activity are for all Americans over age two to accumulate 30 minutes of
moderate-intensity physical activity on most, preferably all, days of
the week. These recommendations were released in 1996 in the Surgeon General's
report, "Physical Activity and Health." They suggest a "lifestyle" approach
to physical activity and health, and they complement earlier guidelines
that called for formal exercise 3-5 times a week, for 15-60 minutes, at
60% to 85% of maximum heart rate. These goals, set by the American College
of Sports Medicine in 1978, are still worth pursuing for higher levels
of fitness, but it is possible to improve your health and maintain good
health with less vigorous activity. The new guidelines provide options
for people who are unwilling or unable to participate in more formal exercise.
Moderate-intensity activities use large muscle groups
and are equivalent to brisk walking (3-3 1/2 mph), swimming, cycling, dancing,
gardening, or doing yard work. (See "Less Vigorous, More Time; More Vigorous,
Less Time" for more examples of moderate-intensity activities.) The full
30 minutes of activity need not be done all at once. Rather, it can be
done in bouts of 10 minutes throughout the day and can be incorporated
into the activities of your daily life. Here are some suggestions for
being more active during the day.
• If you use public transportation, walk an extra few blocks to the next
bus stop before you board. Get off the bus a few blocks early and walk
to your destination.
• Take the stairs instead of the elevator.
• Park your car a little further than usual from the grocery store so
you get a walk between car and store.
• Get up occasionally from your desk during the day to stretch and walk
around. Try to fit in a walk during your lunch break.
• Cut your own grass with a push mower.
• Rake your own leaves.
• Wash your car by hand.
• Use a bike for errands or walk whenever possible.
More and more evidence shows that moderate levels of physical activity
have positive effects on cardiovascular disease, weight control, and diabetes.
Virtually every study of cardiorespiratory fitness shows that the fittest
people—those who can walk the longest on a treadmill—are healthier than unfit people, even if the fit person is overweight. In this case, "healthier" means having lower cholesterol, triglyceride, blood pressure, and blood
sugar levels and living longer. Research also shows that people who follow
the Surgeon General's guidelines for activity are twice as likely to stay
active as are people who begin programs of formal exercise.
Many studies also show that the healthiest person is not
always the thinnest, especially when the overweight person is physically
fit. In one well-known study, researchers compared overweight or obese
fit people (yes, you can be fit and fat) to normal-weight, unfit people.
It turned out that the overweight, fit people were healthier and lived
longer than the lean, unfit people. They had healthier cholesterol levels,
triglycerides, blood pressure, and blood sugar levels. They also had less
diabetes and were 2.3 times less likely to die prematurely.
So often the emphasis is on weight loss to get healthier,
but here's evidence to show that even if you are overweight, you can be
healthy, as long as you are fit. And in many of these studies, fitness
was achieved by individuals who walked for activity at moderate paces
of 3-3 1/2 miles per hour. In some cases they accumulated the 30 minutes
throughout the day, while in other cases they did it all at once.
Whether you choose to exercise vigorously or adopt the
Surgeon General's lifestyle plan for physical activity, it is helpful
to write down your plan and keep records of your progress. Your plan might
include walking to the store for groceries, walking an extra stop before
getting on the bus, or taking the stairs instead of the elevator. Any
intentional change in your activity level, however small it may seem,
will help you on your way toward more activity and better health. The
most important thing is to get started.
Becoming more active is very safe for most people. However,
if you are pregnant or if you are over 69 and are not used to being active,
check with your doctor first. If you are neither pregnant nor over 69
but aren't sure if increased physical activity is safe for you, ask yourself
the following questions:
• Has your doctor ever said that you have a heart condition and that
you should only do physical activity recommended by a doctor?
• Do you feel pain in your chest when you do physical activity?
• In the past month, have you had chest pain at rest, when you were not
doing physical activity?
• Do you ever lose your balance because of dizziness, or do you ever lose
consciousness?
• Do you have a bone or joint problem that could be made worse by a change
in your physical activity level?
• Are you currently taking prescription drugs either to control your blood
pressure or for a heart condition?
• Do you know of any other reason why you should not do physical activity?
For people with diabetes, having neuropathy in your feet may make certain
activities inadvisable. If you have any foot problems, including numbness
in your feet, consult your doctor before increasing the amount of activity
you do (even walking!).
If you answered yes to one or more of the above questions, talk with
your doctor before becoming more physically active.
If you answered no to all the questions, you can be reasonably sure that
you can start becoming more physically active right now. However, if your
health changes at some point so that your answer changes to yes to any
of the questions, ask for advice from your fitness or health professional.
If you answered no to all the questions but currently are not feeling
well because of a temporary illness such as a cold or a fever, delay becoming
more active until you feel better.
When you increase your level of activity, be sure to start
slowly and progress gradually; this is the safest and easiest way to go.
If you need assistance with adjusting your insulin or snacks for activity,
your doctor or diabetes educator will be able to help you.
There is a great deal of emphasis on weight in our society.
Some of it is justified because of the serious health consequences associated
with excess weight, but some of the emphasis has more to do with cosmetic
appeal and simply being thinner. Weight loss is difficult, and there's
no guarantee that you will get down to an "ideal" weight or size, no matter
how hard you try. The good news is that you can still be healthy even
if you are overweight, and this is especially so if you are physically
active and fit.
The benefits of physical activity and the risks of inactivity
are indisputable. Obesity and diabetes have become a deadly combination,
but there is hope. Thirty minutes of moderate physical activity, even
in bouts of 10 minutes accumulated throughout your day, even without weight
loss, can help you manage your health. It's never too late to start, and
there's too much at stake not to give it a try. Good luck.
Richard Weil is an exercise physiologist and a consultant
to the Naomi Berrie Diabetes Center at Columbia Presbyterian Medical Center
in New York City.
Statements and opinions expressed on this Web site are those of the authors and not necessarily those of the publishers or advertisers. The information provided on this Web site should not be construed as medical instruction. Consult appropriate health-care professionals before taking action based on this information.
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