hen Bill Evans moved to Little Rock, the heat got to him and he stopped running. But prompted by a ballooning paunch as he approached his 50th birthday, he bought a bicycle. In early August he started cycling to and from work, about 50 minutes each way, and in just two months he had worked off the 10 extra pounds.
Jim Rippe of Shrewsbury, Mass., a 53- year-old father of three young children who said he "loves good food," maintains 160 pounds on his 5-foot, 9-inch frame by exercising at least 45 minutes a day, virtually every day. On the two occasions when he stopped exercising, he said he gained 15 or 20 pounds in the course of a year.
Steve Blair of Dallas has been running nearly every day for the last 33 of his 61 years, averaging 30 miles a week, to combat a lifelong weight problem. Though he still describes himself as "short, fat and bald," he added that he was as fit as a man of 40 and "would be a lot bigger" if he didn't run.
Each of the above — Dr. William Evans, a physiologist at the University of Arkansas, Dr. James Rippe, a cardiologist at the Center for Clinical and Lifestyle Research in Shrewsbury, and Dr. Steven N. Blair, a fitness researcher at the Cooper Institute in Dallas — specializes in physical activity, fitness and weight control. All three have discovered a fact they say most Americans choose to ignore: that physical activity, combined with a careful diet, is a critically important element in permanent weight control.
While most people know that if they eat more calories than they work off they will gain weight, researchers are now zeroing in on the kinds of exercise that can prevent and treat a weight problem and why.
Nearly all experts say that for most people, becoming physically active alone is not a very efficient way to lose weight.
But studies have repeatedly shown that people who combine a moderate cutback in calories with regular physical activity are not only more successful in achieving their weight goals, but they are are also far more likely to keep off most, if not all, of the unwanted pounds.
At the University of Wisconsin, a recent review of research in the field found that 30 minutes or more of low-intensity exercise could burn more calories and body fat than brief high-intensity exercise that could be sustained for only a few minutes.
The studies also show that weight training, while good for preserving or increasing muscle mass, does not use enough calories to foster weight loss and may actually result in weight gain as muscles enlarge, unless the training is accompanied by a reducing diet.
But because muscles use more calories than fat, preserving the muscles can thwart the gradual gain in body fat and consequent reduction in caloric need that commonly occurs with age.
The Arithmetic of Excess Pounds
Despite the "fitness explosion" of the 1970's and 80's, the average American has become increasingly sedentary. Today, according to some periodic national surveys, Americans actually eat less but also use 400 fewer calories each day than their slimmer forebears did at the turn of the last century.
The arithmetic is simple: with an excess of only 100 calories (the amount in three tablespoons of a premium ice cream) of intake over expenditure each day, multiplied by 365 days and then divided by 3,500 calories (the amount in a pound of fat), the result would be a gain of about 10 pounds a year with no compensatory increase in activity.
"We have systematically engineered activity out of our lives, even to the point of not having to get up to change a TV channel or get out of the car to open the garage door," Dr. Blair said.
According to the Surgeon General's 1996 Report on Physical Activity and Health, 24 percent of Americans do no form of leisure- time physical activity and 54 percent do less than the recommended minimum of 30 minutes of moderate activity on most days, leaving only 22 percent of adults who are physically active for at least half an hour a day.
Dr. Peter Wood, an emeritus professor of medicine at Stanford University, said that neither gluttony nor temptation should be blamed for appetites exceeding the body's needs.
In animals and in people, at low levels of activity the body seems unable to accurately adjust caloric intake to output.
"We evolved an active species, and our appestats, by which we adjust food intake with body needs, seem to function best when we are active," Dr. Wood said. "A positive error in the appestat of only 0.36 percent could lead to an accumulation of 20 pounds of surplus fat by middle age."
Dr. Eric Poehlman, a professor of medicine at the University of Vermont in Burlington, said: "Our gene pool has not changed. Rather, society has changed. We're designed to move. In a society where it is comfortable to be sedentary, the genetically susceptible become obese."
But regular physical activity can diminish that tendency.
"Over time," said Dr. David Williamson, an epidemiologist at the federal Centers for Disease Control and Prevention in Atlanta, "people who report higher levels of activity gain less weight."
For example, among the 51,500 male participants enrolled in the Health Professionals Follow-Up Study, a continuing study of male health professionals, the odds of being overweight were 50 percent lower for the men who were most active, according to reports the men submit every two years. Those who said they watched 41 or more hours of television a week were four times as likely to be overweight as those who watched no more than an hour of television a week.
And in the course of only two years, for each 10 hours of television watched, the men gained a third of a pound in the two-year period.
The Magic Word: Exercise
Most people who want to lose weight focus on eating less. And many studies cite a calorie-controlled diet as the surest route to rapid weight loss.
As Dr. Rippe put it, it is easier for most people to eat 500 fewer calories a day than to add 500 calories of physical activity to their daily lives.
"You have to do a tremendous amount of exercise to lose a small amount of weight," he said. "You would have to walk or run about 35 miles to burn off one pound of fat. People quickly become disheartened by such slow progress."
But in the long run, he added, regular exercise — "about 45 minutes of a moderately intense activity like fitness walking done virtually every day" — is crucial to weight management.
For one thing, the body reacts to a weight- reduction diet as if it were starving and reduces the calories it burns, making it ever harder to lose without further caloric cutbacks and making it easier to regain weight with every dietary lapse.
"For the vast majority who lose weight and keep it off, exercise is not so much how they lost but is critical to how they maintain the loss," Dr. Williamson said. "They adopt a lifestyle of regular physical activity — usually daily — to decrease the chance of regaining."
One good example is the National Weight Control Registry. To be enrolled, a person must have lost at least 30 pounds and kept it off for at least one year. Actually, according to a co-founder, Dr. Rena Wing, who is a psychologist at Brown University in Providence, the 3,000 registrants had lost an average of 60 pounds each and kept the weight off for six years. Many of them have family histories of obesity and were overweight as children.
"Almost 100 percent of them used a combination of diet and exercise to lose weight, and about 95 percent use a combination of diet and exercise to maintain their loss," Dr. Wing said in an interview.
How much exercise? Far more than the recommended minimum. On average they expend 2,800 calories a week through physical activity, the equivalent of walking four miles a day every day, although most use a mixture of different activities, including walking, aerobic dancing, tennis, cycling, running and lifting weights.
Studies also show that vigorous exercise acts as a temporary appetite suppressant, and when hunger returns, caloric intake does not compensate for caloric expenditure.
For example, in a study at St. Luke's- Roosevelt Hospital Center in Manhattan, three obese women who increased their daily caloric expenditures 25 percent by exercising on treadmills lost a quarter of a pound a day for 57 days despite having access to as much food as they wanted.
"If you're not prepared to fundamentally alter your life in terms of average activity, you're very unlikely to maintain a weight loss or to keep from gaining a pound a year as you get older," Dr. Rippe said.
The Weight Seesaw
For anyone trying to lose weight, and for normal-weight people as they age, exercise helps to preserve metabolically active muscle tissue. Dr. Rippe said that muscle tissue was 70 times as "metabolically active" as fat. And the result is that muscle uses far more calories than the same weight of fat.
From 60 percent to 75 percent of a person's daily energy expenditure is accounted for by the resting metabolic rate, the calories the body uses when a person is inactive. The higher the percentage of body fat, the lower the resting metabolic rate; that is, the fewer calories a person needs per pound to maintain a stable weight.
Also, when a sedentary person loses weight through dieting alone, 25 percent to 50 percent of the weight lost is muscle tissue, not fat. But when that person regains lost pounds, all that is regained is fat. So with each upward swing of the weight seesaw, a sedentary person becomes proportionately fatter and the body's resting metabolic rate falls, making it harder to lose what was regained and easier to gain even more weight than was first lost.
In comparing 16 formerly obese women with 16 lean women, Dr. Catherine A. Geissler and colleagues at the University of London found that the formerly obese ate less and had metabolic rates about 15 percent lower than the lean women. But with mild exercise the formerly obese were able to speed up their metabolisms.
Dr. Rippe said that "after age 25, a sedentary person loses half a pound of muscle each year, five or six pounds each decade. By the 40's and 50's, that person's metabolism is slow and it doesn't take a lot to result in middle-aged spread."
But, he noted, muscle mass is preserved "in people who are regularly involved in aerobic activity while losing weight, and those who do strength training can actually increase their lean muscle mass."
The net result is a body that uses more calories even at rest, making it easier to lose weight and to maintain that loss with moderate caloric restriction. To maximize the loss of both fat and pounds, a combination of aerobic exercise and strength training is best, Dr. Rippe said.
Also, Dr. Evans said: "As people grow stronger through exercise, they tend to become physically more active in other ways, for example, by climbing stairs or lifting heavy objects. Exercise doesn't have to be going out for a run. It can be the physical activity incorporated into your daily life. Everything counts."
Burn Fat Before It Stays
Exercise also changes the way the body processes food, making it easier for food to be used for energy rather than stored as fat, according to Dr. Dale A. Schoeller at the University of Wisconsin.
In studies recently completed there, Susanne B. Votruba showed that when a person was active, the fat in a meal tended to be burned for energy, but in a sedentary person, the amount of fat burned went way down and ended up being stored instead of used by the muscles.
In fact, several studies show that people on weight-reduction diets who also exercise stick better to their eating plans. At the University of Chicago, Susan B. Racette and colleagues found that, during a 12-week reducing diet, 13 obese women who participated in a formal exercise program were better able to stay on their diets and lost more weight than did 17 women on reducing diets without exercise.
The kinds and amounts of bodily fuel used during exercise depend on the type of activity and how intensely it is pursued.
But while high-intensity exercise burns the most calories per minute, it is exercise done at low and moderate intensities that can be sustained the longest and thus burns the most calories over all.
Furthermore, a recent study showed that breaking up exercise sessions into shorter bouts — say, 10 minutes at a time four times a day — can foster as much or more weight loss as 40 minutes of continuous exercise.
Dr. John M. Jakicic and colleagues at the University of Pittsburgh reported that among 115 women who completed an 18-month weight reduction program, weight loss was significantly greater among those randomly assigned to do four short bouts of exercise on a treadmill at home than among those assigned to do one long bout of exercise or four short ones at an exercise center. The researchers found that those who exercised at home spent 10 more minutes a week exercising than the other groups.
There is also general agreement that there are psychological benefits of regular physical activity, perhaps a reduction in the anxiety, depression and stress that prompt many to overeat, Dr. Rippe said. "Exercise is an organizing principle," he said. "It says, `Each day I think about my health.' "
And that reminder can encourage people to pay closer attention to their diets.