Swiss Pharmacy

WEIGHT PROBLEMS IN CHILDREN: PHYSICAL ACTIVITY AS PRIMARY PREVENTION

In children and adolescents, small increases in moderate daily physical activity prevent large increases in body fat, as long as caloric intake does not increase to compensate for the increased physical activity.

Adding 10 minutes of walking per day at a speed of 2.5 mph for 1 year without any other changes can prevent body fat gain by children/adolescents of various body weights. As body weight determines caloric expenditure, the same distance walked by smaller children would prevent gaining fewer pounds of fat than a larger child. Therefore, replacement of sedentary time (such as TV watching) with physical activity is an important primary prevention modality for pediatric obesity.

Television Equivalents

An 88-pound child/adolescent substituting 1 hour of TV with 30 min of walking and 30 min of other sedentary activity (other than TV, such as reading) for 1 year would not gain 4.5 lbs of fat. Remarkably, the same substitutions in a 220-lb child/adolescent would prevent the gain of / 1 pounds of fat in a year!

The concept of TV equivalents only works in the prevention of gain in body fat; it does not work in the loss of body fat. Unfortunately the principles of caloric balance for the prevention of a gain in body fat by the expenditure of calories in physical activity do not extend to a loss in body fat because the body adapts to its newer, greater body weight and then defends against weight loss. Thus, primary prevention to avoid body fat gain in the first place requires fewer calories expended as physical activity, than does tertiary prevention to remove the already added/stored body fat.

The question is, would substitution of physical activity for 1 hour of TV viewing each day be enough to prevent pediatric obesity? We believe the answer is "Yes."

Fat gain prevented as a child ages from 7 to 17 years:

-     Using the CDC tables for age-BMI, a 7-year-old boy weighing 59.4 lbs who remains in the 85th percentile of body weight would weigh 1 73.8 lbs (85th percentile) 10 yrs later at age 1 7. However, if the same adolescent weighed 195.8 lbs (95th percentile) at age 1 7, then 22 lbs (difference between the 85th and 95th percentiles) of extra weight would have to be accumulated during growth between ages 7 and 17.

-     Thus, the primary prevention goal in this patient would be to prevent gaining 22 lbs of fat from the age of 7 to 1 7 years (an average of 2.2 Ibs/yr). Note that moving from the 84th percentile to the 86th percentile crosses from the "normal" body weight category to the "overweight" category (the 85th percentile is the threshold line to enter the pediatric overweight category).

Physical activity required to prevent gaining 1 pound of fat:

-     Children expend a net of 1 kcal/2.2 pounds of body weight/mile walked, whereas adolescents use 0.9 kcal/2.2 pounds/mile walked.

-     10 kcal needs to be expended every day for 365 days to equate to about 1 lb of fat.

Physical activity required to prevent gaining 22 pounds of fat from the age of 7 to 17, or gaining 2.2 lbs of fat per year.

-     The amount of walking needed to prevent a gain of 2.2 pounds of fat each year from the ages of 7 to 1 7 decreases from 22 min/day to 8 min/day.

-     The explanation is that body weight increases with age and the greater the body weight, the greater the number of calories expended walking. The caloric cost is greater for moving a heavier object than a light object, as work = force X distance, where force = mass X acceleration. As body mass increases, greater caloric expenditure occurs, and fewer minutes of walking are needed to expend calories.

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