Exercise and Obesity
Stan Reents, PharmD
05/06/2007 09:06 AM
Last Revision: 10/22/2015 10:06 AM
Health statistics show that one-third of Americans are overweight (BMI > 25) and another third are obese (BMI > 30).
The media and the medical profession have identified obesity as not only a personal health issue, but as an impending medical crisis (Manson JE, et al. 2004; Vastag B. 2004). While scientific evidence shows that obesity does have a genetic component, lifestyle factors are probably more important. So, if that's true, then obesity should be preventable and reversible.
A survey of over 21,000 people by Consumer Reports in 2008 seems to support this. They found that people who described themselves as "never fat" and people who described themselves as "formerly fat" had remarkably similar lifestyles:
- regular consumption of fruits, vegetables, and whole grains
- avoidance of high-fat foods
- portion control (ie., eating modest quantities of food)
- regular exercise
EXERCISE FOR OBESITY: DOES IT WORK?
However, many in the scientific and medical community believe that exercise isn't very effective for weight-loss. Certainly, many obese people will tell you that it doesn't work for them.
For example, in a study of postmenopausal women, 12 months of exercise 5 days per week led to only a 1.3 kg weight loss (Irwin ML, et al. 2003). That's not very encouraging.
"But wait," you might be saying, "exercise burns calories, and this is how you lose weight, right?"
So, does exercise work, or not? The short answer to this question is: "it depends."
Of course exercise burns calories, and, it's also true that if more calories are burned than consumed, then body weight will decrease. Even when taken to the extreme, these relationships apply. Consider, for example, Tour de France cyclists: despite an intake of 6000-7000 calories per day, they still lose weight during the 21-day race.
But, when explaining if exercise is effective for promoting weight loss, the story isn't quite that straight-forward. Here's why:
REASONS WHY EXERCISE IS ONLY MODERATELY EFFECTIVE FOR WEIGHT LOSS
The most important explanation why exercise isn't effective for many people trying to lose weight is that exercise represents only a small percentage of the calories burned in any 24-hr period. Even a full hour of vigorous exercise in these people constitutes only about 10-30% of the total calories they burn up in a given 24-hr period. Contrast that to the Tour de France athlete who cycles at a furious pace for 6 solid hours, burning up as much as 9000 calories in a single day.
For Most People, a Single Exercise Session Just Doesn't Burn Enough Calories
Most people burn way more calories during "routine daily activities" (vacuuming, raking, sweeping, washing the car, etc.) than they would during a typical exercise session:
|• routine daily activities
||65 - 75% of the day's total
|• a single exercise session
||up to 30 - 35% if vigorous
||5 - 10%
The fact is, obese people simply aren't as active as thinner people:
In 2005, researchers at the Mayo Clinic found that thinner people were more active each day than overweight people. The subjects wore a specially-designed body suit that tracked physical movement throughout the day, including movements as small as toe-tapping. Scientists call this "non-exercise activity thermogenesis" (NEAT) (Levine JA, et al. 1999). Assessments were made twice per second around-the-clock for 10 days.
The study showed that heavy persons sit about 150 minutes more each day than lean people do. This translates to 350 fewer calories burned each day by the obese person. (Levine JA, et al. 2005).
And claims of a "slow metabolism" are not relevant for the majority of people who are overweight or obese:
A report appeared in the New England Journal of Medicine evaluating the metabolic rate of subjects with a BMI of 27 or greater who claimed to have a "slow metabolism" as their reason for being unable to lose weight. Subjects were monitored for 14 days. The study revealed that these self-proclaimed "slow metabolizers" actually underreported their true food intake by 47% and overreported their physical activity by 51% (Lichtman SW, et al. 1992).
500 CALORIES PER DAY
Certainly, weight loss occurs if more calories are burned than consumed. But, as explained above, even if a person exercises for an hour, they may not lose weight. Why? Because it's a lot easier to consume more calories than you burn.
A simple rule-of-thumb to remember is this:
An excess of 500 calories per day, every day for 7 days, will lead to 1-lb of weight gain per week.
That's how easy it is to gain weight. Stop and think of how many calories are in an average dessert at a restaurant. An excess of 500 calories is not going to make you "feel full." Unless you increased your exercise or physical activity on a day that you consumed excess calories, then you may have exceeded that magical 500 calories per day rule.
Fortunately, the reverse is also true:
If you can create a calorie deficit of 500 calories every day for 7 days, you will lose 1-lb by the end of that week.
OK, weight loss is not quite THAT simple but, still, this is a helpful rule to keep in mind when you dine out. (Remember the Consumer Reports survey above regarding food choices and portion sizes?...)
EXERCISE DOES WORK
Exercise does work. Here are some positive results:
• Distance Running: Obese runners lost an average of nearly 40 kg and dropped their body fat down to 14% as a result of running 95-km (about 60 miles) per week with no dietary changes (Tremblay A, et al. 1984).
These are very impressive results, but very few people are willing to run 95-km per week. Fortunately, it turns out that exercise doesn't have to be punishing to produce effective weight loss:
• Walking: Researchers at Duke University compared running with brisk walking. Overweight adults (average BMI of 29.7 kg/m2) who walked 30 minutes per day at 40-55% of maximum oxygen uptake avoided gaining additional weight. Patients were instructed not to diet during the 8-month study. Subjects in all 3 groups who exercised lost body weight and fat mass, with the group who ran 20 miles/week losing the most. However, when running 12 miles/week was compared with walking 12 miles/week, both groups lost weight and fat mass. Subjects who did not exercise gained about 2.5 lbs. Thus, it appears that brisk walking is as effective as running (Slenz CA, et al. 2004).
WHY OBESE AND OVERWEIGHT PEOPLE SHOULD EXERCISE REGULARLY
Obesity is a risk factor for a lengthy list of other diseases, including hypertension, type-2 diabetes, metabolic syndrome, heart disease, joint problems, and more. These diseases, in turn, promote the development of still more medical problems: hypertension increases the risk of kidney disease and stroke; diabetes leads to problems with vision and peripheral circulation, and on and on.
Even if weight loss is minimal, overweight and obese people should still exercise regularly (after first getting clearance from their physician). Many more health benefits are obtained with regular exercise compared to dieting:
• Aerobic exercise is beneficial for the cardiovascular system. In addition to strengthening the heart, exercise will stimulate the circulation, increase oxygen uptake by skeletal muscle, lower blood pressure at rest, and reverse the process of atherosclerosis. Aerobic exercise can effectively lower blood pressure in obese subjects with hypertension even if no weight is lost.
• Resistance exercise strengthens the bones and maintains muscular strength. It doesn't take much resistance to have a positive effect on bone density: In a study of squash players, simply swinging a light-weight squash racquet produced a noticeable increase in the density of the bones of the dominant arm. Muscle strength is improved by any form of resistance-training (eg., weight-lifting, push-ups, sit-ups, squats, working-out with rubber bands, etc.), but even walking will increase muscle strength in the muscles of the legs and back.
In fact, if there ever was a "magic bullet" in medicine, it would be exercise. William Roberts, MD, then Editor-in-Chief of the American Journal of Cardiology once referred to exercise as:
"an agent with lipid-lowering, antihypertensive, positive inotropic, negative chronotropic, vasodilating, diuretic, anorexigenic, weight-reducing, cathartic, hypoglycemic, tranquilizing, hypnotic and antidepressive qualities".
That was back in 1984 (Roberts WC. 1984). Today, we know that, in addition to all those properties, exercise is also beneficial for cancer, dementia and mental health, osteoporosis, sexual dysfunction, and many other medical problems.
EXERCISE RECOMMENDATIONS FOR WEIGHT LOSS FROM THE AMERICAN COLLEGE OF SPORTS MEDICINE
The standard recommendation for people who are overweight (BMI > 25) or obese (BMI > 30) is, of course, "diet and exercise." But, what exactly does that mean?
In 1995, the American College of Sports Medicine (ACSM) recommended at least 150 minutes of exercise per week for otherwise healthy adults (Pate RR, et al. 1995). That translates to 30 minutes per day on 5 days each week. But subsequent research suggests that 150 minutes per week is not enough for weight loss. Two hundred minutes per week (or more) will not only achieve a greater weight loss, but, more importantly, will do a better job of keeping that weight off (Jakicic J, et al. 1999).
• Aerobic Exercise: A study of post-menopausal women with a BMI > 25 who engaged in aerobic exercise (mostly walking and biking), showed that the amount of body fat lost was proportional to the amount of weekly exercise (Irwin ML, et al. 2003):
|> 195 minutes / week
|136 - 195 minutes / week
|< 136 minutes / week
Exercising 40 minutes per day, on 5 days out of 7, would add up to 195 minutes per week.
EXERCISE RECOMMENDATIONS FOR OLDER OBESE SUBJECTS
People over age 65 rarely follow diet and exercise programs for weight loss. Obesity is increasing among the senior population just as it is for other age groups. This results in significant health and lifestyle concerns.
Weight should be a greater concern for older populations because of the higher occurrence of secondary conditions such arthritis, heart disease, and hypertension. In addition, as a person grows older and experiences a decline in strength, balance, and cardiovascular endurance, any excess weight makes performing activities of daily living more difficult. For these reasons, weight reduction always should be a goal for any older individual who has been classified as overweight or obese.
The American Council on Exercise (ACE) recommends the following for older overweight subjects:
1) Aim to exercise three days per week initially. Gradually work up to five days per week, varying the program on alternating days to prevent boredom.
2) The higher the level of obesity, the more difficult it will be to exercise. Start with 30 minutes of exercise broken down into 10 minutes of cardiovascular activity (eg., walking on a treadmill, stationary cycling), 10 minutes of weight-lifting using 5-10-pound dumbbells, and 10 minutes of flexibility exercises. Increase the duration of each phase of exercise as you become more capable and comfortable with the program. Rest as necessary to prevent premature fatigue.
3) Intense effort is not the goal for elderly people. If you cannot carry on a conversation while walking on the treadmill or riding the exercise bike, you are exercising too hard.
4) If your leg muscles are weak, try non-weight-bearing activities, such as aquatic exercise, and arm and leg cycling.
5) Do not be too concerned about your weight during the early stages of the program. The primary goal is regular exercise.
Hiring a personal trainer, at least during the first few exercise sessions, is highly recommended.
"STEPS" YOU SHOULD TAKE
"Exercise" and "daily physical activity" are separate but complementary behaviors. Both are important for maintaining your weight...and, preventing health problems!
Exercise can be an effective component of a weight-loss program, however, most people simply don't exercise enough to make it work for them. Here are some suggestions for integrating moderate exercise into your lifestyle:
• Walk or bike to the store whenever possible
• Convert the daily task of walking the dog into your daily run and take the dog with you
• Buy a pedometer and wear it daily
• Buy some simple exercise aids (jump rope, exercise bands, exercise watch, running shoes, etc.) and carry them with you when you travel. A really useful all-in-one exercise kit you can take with you when you travel is the FitKit.
• Surround yourself with other people who exercise regularly; develop social circles based on exercise (walking in the mornings, bike trips on weekends, tennis leagues, etc.)
• Stick with your lifestyle change long enough until it becomes a habit
Daily Physical Activity
It turns out that you probably burn way more calories from your routine daily activities (eg., doing laundry, washing the car, vacuuming) than you burn during a single exercise session. Like saving loose change, small amounts of activity throughout the day add up. Here are some suggestions for integrating more movement into your lifestyle:
• Park at the far end of the parking lot
• Take the stairs, not the elevator or escalator
• Carry your bags of groceries to your car instead of using the cart
• Mow your lawn with a push-mower
• If you have a sedentary job, stand up and move around hourly. Buy an activity tracker and wear it daily
SUMMARY and RECOMMENDATIONS
Exercise should be a part of every weight-loss plan. Exercise not only helps you burn calories and lose weight, but it also provides a wide variety of other health benefits, such as lower blood pressure, increased bone density, and a stronger heart, just to name a couple. Also, exercise, if done regularly, helps to keep the weight off after it is lost.
• Exercise at least 5 days per week for a total of at least 150 minutes per week. If possible, exercise 200 minutes per week. Even if no weight is lost, you will be obtaining health benefits (lower blood pressure, for example). Also, it's possible that you are losing fat but this trend is disguised because you are simultaneously adding muscle.
• Exercise does not have to be intense to burn calories. Walking has been shown to be effective. Slow bicycling, however, because most of your body weight is supported, is probably not very effective.
• Remember, it only takes a calorie-deficit of 500 calories per day every day for 7 days to produce a 1-pound-per-week weight loss. But, don't try to lose more than 2 pounds per week. Rapid weight loss is unhealthy. So, if you do the math, it will take you a year to lose 100 lbs. Keep track of your progress by using the BMI Tables.
FOR MORE INFORMATION
An excellent exercise book for consumers is ACSM Fitness Book (Human Kinetics, $16.95). It contains charts for body mass index (BMI) and waist-to-hip ratio.
Readers may also be interested in these reviews:
Use our Exercise Calorie Converter to determine how much exercise is required to burn off the calories in menu items from specific restaurants. We also offer an app that you can install on your mobile device: Mobile Apps
EXPERT HEALTH and FITNESS COACHING
Stan Reents, PharmD, is available to speak on this and many other exercise-related topics. He also provides a one-on-one Health Coaching Service. Contact him through the Contact Us page.
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ABOUT THE AUTHOR
Stan Reents, PharmD, is a former healthcare professional. He is a member of the American College of Sports Medicine (ACSM) and holds current certifications from ACSM (Health & Fitness Specialist), ACE (Health Coach) and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics) and has written for Runner's World magazine, Training and Conditioning, Club Solutions, and other fitness publications.
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