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Obesity, Type 2 Diabetes, and Physical Activity

What's the Connection?

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.

Overweight or obese

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.

Health risks of overweight

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.

What causes obesity?

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?

Reversing obesity

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.

Insulin resistance

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.

Physical activity

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.

Fit and fat

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.

Getting moving now

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.

A word about weight

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.

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