Susan Magocsi, a vivacious 50-year-old Milton psychologist, loves to exercise. She’s training for a walking marathon in Alaska in June. She lifts weights. She does yoga and ballet.

In fact, by a number of measures — such as low cholesterol and blood pressure — she’s admirably fit.

But she loves to eat, too. Eating is “embracing life,” she says cheerfully. “I’m always suspicious of people who don’t like to eat. Where is their spirit, their passion?”

That passion has helped her put on 30 pounds since high school, more than enough to double her risk of problems like diabetes and hypertension. Her body mass index, or BMI, is just shy of the new cutoffs the government uses to define overweight.

She couldn’t care less. “I’m fit and fat,” she says proudly.

Can you really be both fit and fat? Yes, at least some fitness-fatness gurus say, but it depends on how fit and how fat.

There’s no question that Americans today are fatter than ever, and fatter than the rest of the world, too. We’re also lazy: Nearly 80 percent of us don’t accumulate even the minimal exercise — 30 minutes daily — recommended by the government.

A whopping 55 percent of adults 20 and over — or 97 million Americans — are overweight or obese, according to guidelines released last year by the National Institutes of Health in Bethesda, Md. If you’re one of them, you have an increased risk of hypertension, high cholesterol, diabetes, heart disease, stroke, gallbladder problems, osteoarthritis, sleep apnea, and some cancers.

The guidelines, which conform to those of the World Health Organization, say you are overweight if you have a BMI of between 25 and 29.9, and obese if it is 30 or more. (To calculate your BMI, multiply your weight in pounds by 703, then divide the answer by your height in inches, twice — or in other words, by the square of your height.)

Overall, 21 percent of Americans are obese — compared to 14 percent of Canadians and 8 to 10 percent of people in other leading industrialized nations, says Claude Bouchard, a geneticist and obesity specialist at Laval University in Quebec.

But whether you can carry around a pile of extra pounds and still be fit if you exercise is “very controversial,” says Miriam Nelson, associate chief of the human physiology laboratory at the Research Center on Aging at Tufts University.

Bouchard, for instance, believes there is a “zone” in which you can be fit and fat. People with BMIs of 27 to 30, “which is becoming fairly chubby, can have fairly high degrees of fitness,” he says. Beyond that, while a few athletes can have a BMI in the obesity range and be fit, most ordinary mortals that size have too little muscle and too much body fat.

If you’re genuinely obese, weight loss is necessary to achieve optimal health, says Dr. JoAnn Manson an endocrinologist at Brigham and Women’s Hospital. In fact, a 1995 study of 170 obese men directly compared the benefits of weight loss without exercise to those of exercise without weight loss for reducing heart disease risk factors like high blood pressure, high cholesterol and diabetes. Weight loss won.

And last year, the American Heart Association added obesity to its list of major heart disease risks, along with smoking, high cholesterol, high blood pressure, and a sedentary lifestyle.

But other researchers flatly disagree, saying fitness may be more important than weight loss. The most persuasive evidence cited by this camp is an eight-year study of more than 25,000 men published in 1995 by Steven N. Blair, director of research at the Cooper Institute for Aerobic Research in Dallas.

Blair found, not surprisingly, that among men with a BMI of 27 or less, the moderately fit had half the risk of death from all causes as the unfit. The really fit were at even less risk.

But Blair’s team also found that even with a BMI of 27 to 30 and 30 or more, moderately fit and very fit men had lower death rates than unfit men. In fact, the Blair team believes that unfit thin men have a higher risk of death than fit but fat men.

“Although physical activity or exercise may not make all people lean, it appears that an active way of life may have important health benefits, even for those who remain overweight,” the team concluded.

Still, it’s “a rare bird who is both fit and fat,” argues Manson. “Fit and fat is clearly better than unfit and fat. But it’s not as healthy as fit and trim.”

To some degree, the relative merits of getting fit versus losing weight depend on what disease you’re trying to prevent.

Osteoporosis and colorectal cancer are more closely linked to a sedentary lifestyle than to obesity. Uterine and breast cancer in older women, on the other hand, are more tied to weight, because fat tissue makes estrogen, which drives these cancers.

For diabetes and high blood pressure, too, obesity is the big culprit. It leads to insulin resistance, which means the body becomes less responsive to the hormone insulin, which escorts sugar from the blood into cells. Insulin resistance leads to diabetes and salt retention, which raises blood pressure.

The bottom line for most people is that, after quitting smoking, “exercise is the single most important thing you can do to benefit your health,” says Manson. “Exercise increases muscle mass, which increases metabolic rate, even when you’re not exercising, which helps burn more calories.”

Generally speaking, of course, weight loss and fitness go hand in hand. But if you have to choose, she says, “focus on healthy lifestyle behaviors like regular exercise and a heart-healthy diet, not what the scale reads.”

Bouchard, the Quebec geneticist, agrees. Diet and exercise are both critical, he says, but if he had to pick just one, “I’d put my money on increasing the level of activity.

In fact, you’re better off eating 2,500 calories a day and working off the extra 500 than consuming just 2,000 and sitting around all day, says Nelson, the Tufts nutritionist.

Even physical activity as minor as fidgeting seems to help, Mayo Clinic researchers reported in last week’s Science journal. The clinic’s newsletter puts it this way: “Concentrate on being fit and healthy rather than squeezing into your old jeans.”

In other words, even small changes in activity make a big difference in fitness and weight over time. Decreasing energy output by 100 calories a day can lead to a gain of 10 pounds in a year. The reverse is also true: You can lose 10 pounds a year by adding a daily, one-mile walk, which burns 100 calories.

Obviously, you don’t have to choose between losing weight and getting fit. The two go together. But focusing on exercising can make things easier.

“For me to lose weight,” says Susan Magocsi, “I’d have to eat 1,200 calories a day. That’s not having fun. Let’s put fun in here.” For her, that means eating and exercising.

 Sidebar:

Losing it for keeps

In addition to body mass index, the National Institutes of Health recommends taking stock of your waist circumference, which is associated with abdominal fat. A waist measurement of more than 40 inches in men and 35 in women signifies increased health risk in people whose body mass index is between 25 and 34.9, meaning they are overweight or obese.

Though losing weight and keeping it off isn’t easy, behavior therapy to improve eating and exercise habits can help.

The NIH also says:

• You should engage in moderate physical activity, progressing to 30 minutes or more on most, or preferably all, days of the week.
• Cutting back on fat alone can help reduce calories and cardiovascular disease risk. But reducing dietary fat without reducing overall calorie intake won’t produce weight loss.
• Even losing just 10 percent of body weight can reduce many obesity-related health risks.
• If you’re trying to lose 10 percent of body weight, it’s likely to take six months, with a loss of one to two pounds a week.

For more information on the government’s weight guidelines and the body mass index chart, check the web, atwww.niddk.nih.gov

Twenty years ago, the gurus at the American College of Sports Medicine told us to get off our duffs and get those lungs and hearts pumping. Eight years ago, they told us to pump iron, too.

Now, they’ve added a third cornerstone to their fitness guidelines — get flexible.

Don’t groan; it’s long overdue. And while stretching is an addition to, not a substitute for, the aerobic exercise and weight lifting we should already be doing for health and fitness, it’s arguably the easiest and most enjoyable exercise of the lot.

And if it’s just looser limbs or a better golf swing you’re after — as opposed to yoga-like inner peace — you can even do your stretches while doing something else, like watching TV.

In case you haven’t noticed, one of the less pleasant features of aging is that creakiness called decreased range of motion. If you can’t move your limbs, head, and trunk through a full range of motion, exercise physiologists say, you’re setting yourself up for orthopedic problems, including low back pain and injury.

It’s also just plain demoralizing if your shoulders get so tight that brushing your hair becomes an Olympic event or your hamstrings become so taut the mere words “bend over and touch your toes” send you back to the couch for another decade.

The solution, the sports medicine folks declared several weeks ago, is flexibility training.

For the record, there are no clinical studies proving the benefits of flexibility training. In fact, compared to the data on aerobic exercise and strength training, the data on flexibility is scant, says William Evans, director of the nutrition metabolism and exercise program at the University of Arkansas Medical School.

But studies are piling up fast enough to justify adding flexibility training to the standard fitness regimen, says Glenn A. Gaesser, an exercise physiologist at the University of Virginia and a co-author of the new guidelines.

For one thing, it’s clear that connective tissue benefits from stretching — or at least suffers from lack of it. In women who wear high heeled shoes, tendons, ligaments — and muscles — become so shortened that walking uphill may produce cramps or injuries to calf muscles.

For another, it’s been demonstrated many times in animals that stretching a muscle triggers growth factors that increase the number of tiny, contractile protein filaments inside each muscle cell.

These actin and myosin filaments slide over each other or pull apart, grabbing on to (“cross-linking”) each other at intervals. This lets the muscle cell contract or extent with controlled ratcheting action.

Muscle cells also have mechanisms called spindle receptors that sense where the muscle is in space and how much tension — or muscle tone — it has. When you stretch a muscle suddenly, or too far, these receptors send out an alarm, telling the muscle to contract immediately to protect itself against injury.

But if you stretch carefully, you can train these receptors to pause before firing, allowing the muscle to get longer — grow — without reflexively tightening.

Muscle physiologists have identified three kinds of stretches: static, ballistic, and PNF, or proprioceptive neuromuscular facilitation.

Ballistic stretches, in which you bob or bounce while trying to do something like touch your toes, are not widely recommended because they can cause muscle injury.

But static stretches are safe. It’s a static stretch if you sit on the floor with your legs extended and slowly try to touch your toes, holding the stretch 10 to 30 seconds.

PNF stretches are also safe, but are more complicated and often require a partner. For instance, as you sit on the floor with your legs extended, your partner pushes on your back while you push against him, contracting your muscles for about six seconds. Then you do a static forward stretch for 10 to 30 seconds.

The idea is that by contracting your muscles first, you re-set the firing threshold of the stretch receptors in muscle fibers so that it takes more stretch to make them fire.

Not all exercise physiologists use PNF stretches in their practice, in part because they believe static stretches are almost as effective.

Some gurus swear by yoga as the best approach to stretching, and yoga is “an excellent way to develop flexibility,” says James Graves, chairman of the exercise science department at Syracuse University.

But it’s not the only approach, and a simple 20-minute routine that stretches major muscle groups two to three days a week also works fine. It’s also best to stretch after your muscles are already warmed up.

If you want to try yoga, shop around for a teacher you like, advises Betsey Downing, a sports psychologist who runs the Health Advantage Yoga and Personal Development Center in Herndon, Va.

A good teacher, she says, is one who knows anatomy and can offer precautions and alternative stretches if you have an injury or problem doing a particular move.

There’s no universally-accepted certification program for yoga teachers, so it makes more sense to ask a teacher about his or her experience and approach — there are dozens of varieties of yoga — than about credentials per se.

And beware of teachers, and stretches, that cause pain. It’s fine to feel that your muscles are working. But sharp pain — particularly in the joints or at the points where the muscle attaches into the bone — is a sign of injury, not progress.

SIDEBAR:

What it takes to be fit:

When the federal government issued its 1995 exercise guidelines, it had the modest goal of lowering people’s risk for chronic conditions like hypertension and diabetes. The American College of Sports Medicine guidelines have a more ambitious goal: fitness.

The feds call for accumulating at least 30 minutes of moderate activity on most days. This means you can add up a 10-minute walk, 10 minutes of gardening, 10 minutes of chasing the kids around the playground.

The sports medicine guidelines are tougher — aerobic workouts of less than 20 minutes don’t even count.

And while the feds focus on mild aerobic exercise, the sports medicine group recommends aerobics plus strength training and, as of a few weeks ago, flexibility training as well. You can do the minimum level of all three in roughly three hours a week.

For overall fitness, here’s what they recommend:

Aerobic, or cardiovascular conditioning.

• Frequency — 3 to 5 workouts a week. Fewer than three won’t be enough, more than five will add little.
• Intensity. The goal is to work fairly hard, at 55 to 90 percent of your maximum heart rate. To estimate this, subtract your age from 220. If you’re 50, this yields 170. If you want to work out at 75 percent of your max, multiple 170 by 75 percent, which gives 128 beats per minute.
• Duration. Workouts should last 20 to 60 minutes.

If you must cut corners on aerobics, sacrifice duration first; for example, chopping a 40 minute workout to 30. If you have to cut more corners, sacrifice frequency; drop from five days a week to three or four. Don’t sacrifice intensity.

Strength training, or using weights or machines to build muscle mass, two to three days a week. In each session, work each muscle group eight to 10 times.

For instance, to work the quadriceps, the big muscles in the front of the thigh, do knee extensions (sit in a chair and lift the foot against resistance, either a weight or a machine).

Other major muscle groups to work include the hamstrings, abdominals (that means bent-leg sit ups), chest presses (push ups or bench presses) and rowing-type exercise in which you use the upper body to pull weight toward you.

You also need to work the back muscles, either pushing up against a machine or lying on your belly, hooking your feet under the bed, and arching up so your chest is off the floor.

For arms, try biceps curls and triceps manoevers (hold a weight in your hand with your arm straight up over your head; bend your elbow so your hand brushes your shoulder; then extend it up.)

Flexibility training, or stretching the major muscles groups at least four times, two or three days a week.

You head out the door, virtue personified, for the first run, or at least brisk walk, of the year.

You know — who doesn’t by now? — that regular exercise is great for your heart, your muscles, your mental health.

You may even think — as exercisers usually do — that working out is a tonic for your immune system. Indeed it may be, provided you don’t push yourself to the max too often.

But as the once-tiny field of research into exercise and immunity blossoms — the two-year old International Society of Exercise and Immunology wrapped up its second meeting in Europe recently — researchers are finding that the links between exercise and immunity are more slippery than once thought.

The emerging picture, they say, is that any connection between exercise and, say, the risk of getting a cold, probably follows a J-curve, with both too little and too much exercise being deleterious, and moderate exercise, potentially beneficial.

But caveats are in order.Compared to research on exercise and heart function, the study of exercise and immunity is in its infancy. Just figuring out what to measure is tricky

because exercise varies in type, intensity and duration, people vary in basic fitness and the immune system is one of nature’s most complex creations.

Links between exercise and immunity are “interesting, but speculative,” says Dr. Jerome Groopman, chief of hematology and oncology at Deaconess Hospital.

“What’s required is a very critical look at how immune function is measured in these studies,” he says.

Some studies do show that the activity of some immune cells “can be affected by exercise,” says Roger Fielding, an exercise physiologist atBoston University. The problem is how to interpret this.

Blood counts of immune cells called neutrophils, for instance, “go up if you do a bout of exercise,” Fielding says. But this may only be a sign that the inflammatory process by which the immune system repairs exercise-induced muscle tears is working, not a sign the body is better primed to fight infections or cancer.

With other measures, like observed increases in natural killer cells, it’s unclear whether changes are big enough or last long enough to impact immunity, he says, adding, “I’m very skeptical.”

Still, the consensus is that regular, moderate exercise “will boost some aspects of immune function,” says William Evans, director of the Noll Physiological Research Center at Pennsylvania State University in University Park. “And it’s likely that people who exercise regularly have lower rates of certain kinds of cancer and greater resistance to infection.”

Studies from Texas, for instance, show that deaths from all causes — including cancer — are lower in people who are regular, moderate exercisers than in sedentary people.

“There’s also evidence,” says Evans, “that people who exercise regularly have higher levels of IL-1, a natural substance that raises body temperature — producing fever — and helps kill invading organisms.

David Nieman, professor of health and exercise science at Appalachian State University in Boone, N.C., has been finding growing evidence of links between exercise and immunity.

In two randomized, controlled studies, Nieman, president-elect of the exercise and immunology society, compared overweight, sedentary women who began a program of brisk walking for 45 minutes, five days a week, with matched controls who remained sedentary. He found the walkers suffered only half as many sick days for colds as the others.

More intriguing, Nieman found that the number of immune cells — some of which normally live in the spleen and lymph nodes — increased temporarily in the walkers’ bloodstreams. There, at least in theory, they’d be more available to fight off germs.

Other researchers have shown that “graded exercise” may help people with HIV infection or chronic fatigue and immune dysfunction syndrome (CFIDS) — perhaps by improving mood, which in turn may influence immune function. But this remains unproven.

Dr. Leonard Calabrese, head of clinical immunology at Ohio’s Cleveland Clinic, has found that his chronic fatigue patients feel better if they walk a bit — three to four minutes a day — and increase this by one to two minutes every two weeks.

Graded exercise seems to benefit people with HIV infection, too, provided they are in decent shape to start with.

Among Calabrese’s HIV patients, exercise seems to boost natural killer cells and at least does not decrease the number of CD4 cells, the main type of immune cell attacked by the AIDS virus.

Weight lifting, he finds, doesn’t seem to affect the immune system, though it helps retain lean body mass.

And as with so much else in life, however, if you overdo it, exercise can become too much of a good thing. In fact, though many peopleexercise too little, some do far too much, especially world class athletes who, says Evans of Pennsylvania, “are always on the edge of overtraining.”

“Excessive exercise can backfire,” agrees Dr. Kenneth Cooper, founder of the Cooper Aerobics Center in Dallas. He believes too muchexercise stimulates an outpouring of free radicals, chemicals formed in the body when oxygen is burned.

Whether free radicals — which the body fights by increasing production of anti-oxidant enzymes — impair immune function is not clear, but Cooper
recommends taking anti-oxidant supplements anyway, though others say the data to justify this is incomplete.

At the very least, there’s growing evidence that athletes who push too hard for too long seem to be more susceptible to colds.

In 1987, Nieman surveyed 2,311 runners training for the Los Angeles marathon, including in his study both those who raced and those who dropped out for nonmedical reasons. He found that those who raced were six times more likely to get colds afterwards, a sign of how stressful the long race can be.

To see which immune components might be involved, he then coaxed 50 marathoners into his lab — by offering $100 a head — and asked them to run for 90 minutes to three hours on a treadmill at 80 percent of maximum aerobic capacity.

By measuring blood levels of immune cells — neutrophils, monocytes, natural killer cells, T cells and B cells — before and after the run, he found immune cells “leave the blood and go to muscles,” presumably to repair damaged muscle fibers.

This suggests, he says, that the risk of infection may increase temporarily after a long, hard workout because “the front lines don’t have as many soldiers,” though immune function does bounce back to normal nine to 24 hours later.

Nieman also measured runners’ levels of cortisol, a hormone and powerful immunosuppressant that soars in response to both mental and physical stress. He found that after a 3-hour morning run, cortisol soars and stays high all day.

For that reason, Nieman recommends that exercisers stay out of “cortisol country.” The way to do that, his studies show, is to work out at 70 percent of your maximum heart rate for no more than 90 minutes per session.

The bottom line, says exercise physiologist Edmund Burke at the University of Colorado, is that while exercise is necessary, if done to excess “it’s a double-edged sword.”

And while most of us need to hear primarily the first half of that message, some need to hear the last.

Indeed, Bicycling magazine, citing two small but alarming studies in Poland and Australia, recently warned that while riding hundreds of miles a week leads to fitness, it may also lead to impaired immunity.

Nieman came to that same conclusion two years ago. After running 58 marathons, he quit. “My own research was convincing me it was not a healthy thing to do,” he said.

To increase fitness without damaging muscles or the immune system, exercise physiologists suggest several DOs and DON’Ts:

SIDEBAR:
EXERCISE: THE RIGHT WAY AND WRONG WAY TO DO IT

DOs

• Spend at least 30 minutes on moderate physical activity on most, preferably all, days — brisk walking, cycling, swimming, yard work, etc. — either continuously or in 10-minute bouts.
• If you run, a good goal is 10 to 15 miles a week. More than that won’t boost longevity or health, and running more than 30 miles a week may be detrimental.
• To maintain muscle mass and bone density, lift weights two to three times a week. Weights should be heavy enough that you can only lift them 8 to 10 times before needing a rest.
• For cardiovascular conditioning, keep your heart rate at 65 to 90 percent of maximum for 30 minutes, three to five times a week. To find the right range for your heart rate, subtract your age from the number 220, then multiply the result by 0.65 to get the minimum, by 0.9 for the maximum.
• If you have a serious disease such as HIV infection, chronic fatigue syndrome or cancer, ask your doctor about exercising. Moderateexercise, under supervision, may be beneficial.
• Eat a balanced diet, with lots of fruits and vegetables, and allow time for sleep and rest.
• The data is incomplete, but some specialists recommend anti-oxidant supplements if you exercise heavily: 1,000 milligrams a day of vitamin C, 400 International Units of vitamin E and 25,000 International Units of beta- carotene.
• Follow the NECK UP rule for exercising with a cold — if symptoms are primarily nasal, exercise as usual.

DON’Ts

• Don’t exercise if you have symptoms below the neck such as a bad cough or a fever or muscle aches. Muscle aches may be a sign of infection with the coxsackie virus; exercise can cause this virus to migrate to the heart, with potentially fatal consequences. If you’re coughing from bronchitis, exercise may trigger asthma.
• Don’t exercise hard for any more than 90 minutes at a time to avoid release of cortisol, a stress hormone and immune suppressant.
• Don’t over train lest you compromise immunity, especially if you have other stresses like major job problems or divorce.
• Don’t expose yourself to unnecessary germs if you’re training hard. Avoid crowds when you can, wash hands and disinfect things other people touch, like telephones, door knobs or keyboards.
• Don’t lose weight too fast. Losing more than two pounds a week may compromise T cells. If you exercise and starve yourself, your body may interpret this as stress and pump out cortisol.