Exercise and Middle-Age Spread

Men's weight goes up and their waistlines grow as they reach middle age, even if they're dedicated runners, according to a study of male joggers.

At any given age between 18 and 49, men who ran more miles per week did tend to be leaner than those who ran fewer. But even among the most active group -- men who ran more than 40 miles a week -- weight and waist circumference tended to increase steadily throughout the 20s, 30s and 40s.

The message: a man can beat middle-aged spread if he escalates his exercise regime as he ages, said Paul T. Williams, an epidemiologist at California's Lawrence Berkeley National Laboratory who performed the study.

''If you look at some dietary guidelines, they talk about 'keeping active,' '' said Williams.

But ''keeping active may not be sufficient. You have to become more active as you get older.''

He is currently studying women runners to see if the same advice applies to them.

The study suggests that a man would need to increase his weekly running distance by about 1.4 miles each year to keep his waistline from growing, Williams said. For example, someone who averaged 10 miles per week at age 30 would have to increase his distance to 24 miles per week by age 40.

And this middle-age spread is important, said Williams, because weight gain -- particularly in the abdominal region -- is associated with an increased risk of heart disease, diabetes and certain kinds of cancer.

However, even if you're not increasing the amount of physical activity you do, experts note that you're still doing your health a lot of good with even a steady regimen of exercise.

Canada's Physical Activity Guide, for example, says that three short daily bursts of 10-minute activity periods -- like walking up stairs -- can even improve your health.

In the National Runners' Health Study, Williams set out to examine whether maintaining a steady exercise level as a person ages is enough to keep the pounds off. His findings were published in the an issue of the American Journal of Clinical Nutrition last year.

The study enrolled 4,769 male runners who were between the ages of 18 and 49 and 2,150 who were 50 or older. Participants (with the help of their doctors) provided information about how far they ran each week, whether they had a family history of obesity, their diet, their alcohol intake, their blood pressure and their lipoprotein levels (blood proteins, such as LDL and HDL, that transport fat and cholesterol in the circulation).

None of the participants were smokers. Because very few non-white runners signed up for the study, the researchers limited their analysis to white men.

Participants' waist and hip circumferences were measured, and each person's weight and height were used to calculate his body mass index (weight in kilograms per square meter of surface area). Using BMI simplified comparisons among men of different heights.

At every age, men who ran more miles each week tended to weigh less and have smaller waists than their counterparts who ran less. But within each distance category, runners' weights and waistlines tended to increase steadily with age.

Every additional year of age was associated with an average increase of seven- hundredths of an inch in men's waistlines, and of .045 in BMI.