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Fitness Tip of the Day!
Fat vs. Fit?
The Cooper Institute published a study in 2004 showing that the health risks associated with an elevated BMI are reduced in diabetics if their fitness level is high (Diabetes Care, 2004). So, get out there and walk, run, bike, swim, play tennis or do anything that gets your heart rate up!


Exercise and Obesity

Author: Stan Reents, PharmD
Original Posting: 05/06/2007 09:06 AM
Last Revision: 08/28/2015 11:39 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 is 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


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.


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 race.

But, in obese subjects who are attempting to lose weight with exercise, the story isn't quite that straight-forward. Here's why:


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.

In the average person, "routine daily activities" (vacuuming, raking, sweeping, washing the car, etc.) are responsible for the largest share of the calories expended each day:

  • Calories burned during daily activity: 65-75% of the day's total
  • Calories burned during exercise: none if sedentary; up to 30-35% if exercise is vigorous and prolonged
  • Calories burned during digestion: 5-10%

Unfortunately, obese people simply aren't as active as thinner people:

In 2005, researchers at the Mayo Clinic found that thinner people were more active 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 "NEAT": non-exercise activity thermogenesis (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:

In 1992, 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).


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).


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 4.2%
136 - 195 minutes / week 2.4%
< 136 minutes / week 0.6%

Exercising 40 minutes per day, on 5 days out of 7, would add up to 195 minutes per week.


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.


Weight loss occurs if more calories are burned than consumed. But, even if a person exercises for an hour, they may not lose weight if they consume an excessive number of calories that day.

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.

This is how easy it is to gain weight. Stop and think of how many calories are in an average dessert at a restaurant. 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.

Now, it's not quite THAT precise but, still, this is a helpful rule to keep in mind when you dine out. To help even more when dining out, use our Exercise Calorie Converter app. A quick check of how long you have to exercise to burn-off the calories in a particular item might help you make better choices. (Remember the Consumer Reports survey above regarding food choices and portion sizes?...)


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. Like saving loose change, small amounts of activity throughout the day add up. Here are some suggestions for integrating moderate exercise 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

• 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

• 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


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 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.


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.

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


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.


Irwin ML, Yasui Y, Ulrich CM, et al. Effect of exercise on total and intra-abdominal body fat in postmenopausal women. JAMA 2003;289:323-330. Abstract

Jakicic JM, Winters C, Lang W, et al. Effects of intermittent exercise and use of home exercise equipment on adherence, weight loss, and fitness in overweight women. JAMA 1999;282:1554-1560. Abstract

Levine JA, Eberhardt NL, Jensen MD. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science 1999;283:212-214. Abstract

Levine JA, Lanningham-Foster LM, McCrady SK, et al. Interindividual variation in posture allocation: possible role in human obesity. Science 2005;307:584-586. Abstract

Lichtman SW, Pisarska K, Berman ER, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med 1992;327:1893-1898. Abstract

Manson JE, Skerrett PJ, Greenland P, et al. The escalating pandemics of obesity and sedentary lifestyle. Arch Intern Med 2004;164:249-258. Abstract

Pate RR, Pratt M, Blair SN, et al. Physical activity and public health. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine JAMA 1995;273:402-407. Abstract

Roberts WC. An agent with lipid-lowering, antihypertensive, positive inotropic, negative chronotropic, vasodilating, diuretic, anorexigenic, weight-reducing, cathartic, hypoglycemic, tranquilizing, hypnotic and antidepressive qualities. Am J Cardiol 1984;53:261-262. Abstract

Slentz CA, Duscha BD, Johnson JL, et al. Effects of the amount of exercise on body weight, body composition, and measures of central obesity. Arch Intern Med 2004;164:31-39. Abstract

Slentz CA, Bateman LA, Willis LH, et al. Effects of aerobic vs. resistance training on visceral and liver fat stores, liver enzymes, and insulin resistance by HOMA in overweight adults from STRRIDE AT/RT. Am J Physiol Endocrinol Metab 2011;301:E1033-E1039. Abstract

Tremblay A, Despres JP, Bouchard C. Adipose tissue characteristics of ex-obese long-distance runners. Int J Obes 1984;8:641-648. Abstract

Van Etten LMLA, Westerterp KR, Verstappen FTJ, et al. Effect of an 18-wk weight-training program on energy expenditure and physical activity. J Appl Physiol 1997;82:298-304. Abstract

Vastag B. Obesity is now on everyone's plate. JAMA 2004;291:1186-1188. Abstract


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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