Bones don't suffer when fat is lost through exercise

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Bones don't suffer when fat is lost through exercise

26 May 2005 Medical News Today

Debunking the myth that exercising to lose excess body fat, unlike

dieting alone, comes at a cost to bone health, researchers at s

Hopkins have determined that for those age 55 to 75, a moderate

program of physical exercise generally maintains bone mass and, in

some cases, offers modest improvements.

The Hopkins team showed, in a study to be published in the June issue

of the American Journal of Preventive Medicine, that after six months

of aerobic exercise on a treadmill, bicycle or stepper, plus

weightlifting, subjects experienced better overall fitness and fat

loss without much change in bone mineral density. A more detailed

analysis revealed slight gains in bone mass, of 1 percent to 2

percent, for those who exercised hardest and showed the greatest

increases in aerobic fitness, muscle strength and muscle tissue.

The Hopkins study is believed to be the first to evaluate the effects

of exercise independently from other factors, primarily diet, on bone

mineral density, a strong gauge of bone health, against the risk of

osteoporosis and bone fracture. Indeed, the researchers believe that

more intense exercise may demonstrate significantly increased bone

mass.

" Older people are very concerned about how best to reduce their body

fat as a means of preventing other health problems, such as heart

disease and diabetes, " says lead study investigator and exercise

physiologist Kerry , Ed.D., a professor of medicine and

director of clinical exercise physiology and heart health programs at

The s Hopkins University School of Medicine and its Heart

Institute. " However, excess fat does have the benefit of maintaining

bone mass. But fat loss through diet alone can lead to loss of bone,

worsening the body's natural bone loss due to aging, a major risk

factor for bone fractures. "

According to , most existing studies about the effects of

exercise on bone had several limitations to their findings. Many

enrolled only women, for example, who are more prone to bone loss

after menopause. Others combined dieting and exercise, obscuring the

source of the impact. None examined the effects of exercise on bone

while also factoring into account the weight and fat changes

resulting from it.

For a six-month period, the Hopkins team assessed the benefits of a

supervised program of exercise training in a group of 104 older men

and women, measuring both fitness and fatness levels at the start and

end of the study. All of the participants were in general good health

except for untreated, mild hypertension. Half were randomly placed in

a widely recommended moderate exercise program, believed to improve

fitness, heart health and body composition, while the rest maintained

their usual physical routine and diet.

The active group participated in a supervised series of exercises for

60 minutes, three times per week. The combination of exercises was

designed to work all major muscle groups, the heart and circulation.

Substantial improvements were observed in active participants' body

fat, and muscle and fitness levels.

Aerobic fitness, as measured by peak oxygen uptake on a treadmill,

increased by 16 percent, and strength fitness increased by 17

percent. The average weight loss in this group was only four pounds,

because much of the loss of fat was offset by increased muscle mass.

The fat in the abdominal region, measured by magnetic resonance

imaging, was reduced by 20 percent among exercisers. The group that

was not exercising had either no or significantly less improvement

than the exercising group.

Bone scans, using an X-ray machine called DXA, were used to assess

bone mineral density. Measurements were taken of the total skeleton

and in areas most vulnerable to bone loss and subsequent fracture,

including three locations on the hip, and one in the spine. In both

men and women who exercised and lost weight, overall bone density did

not change, although results were mixed for women in specific sites

of the hip. However, those who showed the greatest gains in fitness

had modest gains in bone density at several sites, and loss of body

fat was not associated with bone loss.

According to , an increase in bone mineral density among older

exercisers has been observed in previous studies, but this increase

was lacking in the current study because the fitness program was

probably of too low intensity or too short in duration.

" Older people will likely have to exercise either harder or for

longer than six months for there for there to be a substantial

increase in bone density, " says study co-author and endocrinologist

Suzanne Jan de Beur, an assistant professor at Hopkins who

specializes in bone health. " Our results show that moderate-intensity

exercise can increase fitness and reduce body fat, which are

important for overall health, but gains in bone density were found

only among those who achieved the greatest gains in fitness in six

months. Fat loss with exercise did not result in a loss of bone mass,

a problem commonly seen when patients lose weight with diet alone. "

Jan de Beur adds that while bone mass did not increase in this

program, there are other benefits that will likely reduce the risk of

fractures. Bones commonly break after a fall, a major risk factor for

fractures in older people. But exercise makes bodies stronger and

improves balance, thus preventing falls.

The Hopkins study's exercise program followed current guidelines from

the American College of Sports Medicine. The study was part of a

larger, ongoing trial, called the Senior Hypertension and Physical

Exercise study (or SHAPE, for short). It is believed to be the first

detailed examination of the guidelines' effectiveness and gender

differences in the effects of exercise, with nearly an equal number

of men and women enrolled.

Funding for the study was provided by the Heart, Lung and Blood

Institute, a member of the National Institutes of Health (NIH), with

additional assistance from the s Hopkins Bayview General Clinical

Research Center, also funded by the NIH. Other Hopkins researchers

who took part in this study were Anita Bacher, M.S.N., M.P.H.;

Hees, Ph.D.; Tayback, Sc.D.; and Pamela Ouyang, M.D.

s Hopkins Medical Institutions

http://www.hopkinsmedicine.org