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READERS' FORUM

The best way to calculate body fat?

"Aiming for healthy weight in wrestlers and other athletes" (September 2001) is a timely article on a subject pediatricians need to know about. I have one question and one comment for the author: How accurate are automated calipers? And, second, the calculations for percent body fat take a long time to do and give figures that aren't always reasonable because they don't take into account bone frame size and muscle mass.

Jon E. Dennis, MD
St. Cloud, Minn.

The author replies: Automatic calipers measure the skin folds very accurately, assuming good technique is used, as described in the article. The problem is that the formula in the computer chip to calculate body fat has not been validated in youngsters of high school age. In my opinion, utilizing automatic calipers is better than not measuring body fat at all. The Lohman equation provides more accurate results for determining body fat in wrestlers, however.

Dr. Dennis is correct that the calculations for determining percent body fat and minimum weight from skin-fold measurements can be laborious. Jon Almquist (JLAACT@aol.com) has a program that allows you to calculate body fat, minimum wrestling weight at 7% body fat for males, and even maximum weight loss per week of 1.5% of body weight. All you do is input skin-fold measurements and weight.

One advantage of skin-fold measurement over the other methods for measuring body fat listed in Table 4 is that muscle mass and bony structure do not alter body fat determination. Because body fat is the only component beneficial to lose, skin-fold measurements provide the information needed to analyze body fat.

Vito A. Perriello, Jr., MD

Different angles on sleep position

"Another angle on sleep position" (Clinical Tip, September 2001) gives advice that may be dangerous for many infants. In this clinical tip, Dr. Goddard suggests elevating the baby's head to 30° in the supine position by placing something under the mattress or putting the infant in a car seat for sleeping.

It is well known that premature infants in an upright position are at increased risk for oxygen desaturation, apnea, and bradycardia. Because of these problems, the American Academy of Pediatrics recommends that all infants born at <37 weeks' gestation be monitored and observed in a car seat before discharge. Some physicians, including myself, are concerned that even infants closer to term could experience these problems in an upright position, especially over an extended period.

Most car seats are designed to put a newborn at a 45°, not 30°, angle, when placed on a level surface, and it is recommended that a rear-facing, infant car seat be initially placed in a vehicle at a 45° angle for newborns. One may place it in a more upright position as the child grows and develops. As a trained car safety seat technician, I know that many parents have the car seat for their newborn placed improperly in an upright position of more than 45°. When used as an infant seat or carrier, parents often prop up the car seat even more "so the infant can see better."

Merchant and colleagues (Pediatrics 2001;108:647) found that in both 50 healthy, nonmonitored preterm infants (approximately 36 weeks' gestation) and 50 full-term infants, mean oxygen saturation values declined significantly—from 97% in the supine position, to 94% after 60 minutes in a car seat. In fact, "seven infants (three preterm and four term) had oxygen saturation values of <90% for longer than 20 minutes in their car seats. Twelve percent of the preterm . . . but no [full] term infants had apneic or bradycardic events in their car seats."

These data caution against distant travel in a car seat, extended upright positioning in infant seats or carriers, and long periods in a baby swing or any other upright seating device during the first few months of life. The use of a car seat for routine sleeping cannot be recommended in the neonatal period and could be dangerous for a preterm infant.

Charles A. Jennissen, MD
Des Moines, Iowa

Routinely placing infants in a car seat in a crib could lead to ventilatory compromise and hypoxia (Merchant et al: Pediatrics 2001; 108:647) and is an ineffective treatment for gastroesophageal reflux (GER) (Orenstein et al: N Engl J Med 1983;309:760). No clinical evidence supports the recommendation to elevate the head of the infant's bed on a routine basis. In contrast, placing an infant prone with his or her head elevated is an effective treatment for GER (Orenstein et al: J Pediatr 1983;103:534). However, because prone positioning increases the risk of sudden infant death, I usually recommend that infants with documented GER be positioned with their head elevated and supine or, if that doesn't work, with their head elevated and right side down with arm outstretched.

Jonathan Lukoff, MD
Mission Viejo, Calif.

Like Dr. Goddard, I counsel families to elevate the infant's head. However, I no longer recommend using a car seat in the crib because of concerns about compromising the airway and air exchange in very young infants with poor neck and truncal tone. I also have concerns that elevating a mattress using a prop under the mattress may create enough space for entrapment to occur. I advise parents to elevate the head of the crib by elevating the legs at the head end of the crib.

Annamaria Church, MD
Detroit, Mich.

The author replies: In response to Dr. Jennissen's comments, I obviously do not recommend car seat positioning for premature infants whose neck tone is insufficient to prevent breathing problems if their head were to fall forward, chin to neck. My recommendation is for full-term infants who have symptoms of colic or gastroesophageal reflux, such as cough or nasal congestion, spitting up, frequent hiccups after feeding and after sufficient burping, rumination, and, in the setting of GERD–related Sandifer syndrome, neck stiffening when lying flat.

When making recommendations about infant car seats we have to use common sense and give parents some credit. They certainly will travel with their babies. Our newborn nursery has basinettes that can be adjusted to incline the infant's head 20° to 30°; new moms rave about how their newborn sleeps more comfortably in the head-raised position.

Charles M. Goddard, MD

Steps to healthy weight loss

As noted in the November 2001 Readers' Forum, the Guide for Patients that accompanied the article "Aiming for healthy weight in wrestlers and other athletes" (September 2001) contained an error. A corrected version of that guide appears below.

GUIDE FOR PATIENTS

Steps to healthy weight loss

There are no short cuts to losing weight effectively and safely. Weight gain and loss are directly related to the balance between the calories you take in and the calories you burn through daily activity and specific exercise, such as sports.

A government-sponsored task force recently reviewed the multimillion-dollar industry of fad diets that guarantee quick weight loss using everything from vibrators to pills. The task force concluded that although some of the diets may contribute to weight loss, none maintains weight loss (keeps weight off once you lose it). Eating less fat (meat, cheese, and whole milk, for example) and more complex carbohydrates (bread, cereal, pasta), along with regular aerobic activity, appears to offer the best hope for losing weight and keeping it off.

Losing excess body fat should be your only goal in losing weight. Losing water or fat-free tissue, such as muscle, is not desirable or healthy and does not improve performance or appearance.

Eat right

Most adolescents need 1,700 to 3,000 calories a day just to meet physiologic needs and support growth and normal daily activities. The minimum number of calories varies somewhat based on size, as shown on the graph.

An average 30-minute period of aerobic exercise, such as jogging, burns about 350 calories; an intense two-hour sports practice can burn more than 1,000 calories. The table below shows about how many calories various activities consume. The number of calories burned can vary to some degree depending on your weight and how long and intensely you exercise. The minimum calorie requirements suggested here support only usual daily activities. You must consume additional calories if you participate in aerobic activities such as athletics, dancing, or strenuous work.

Calories burned by various activities

Teenagers need to eat a balanced diet that consists of carbohydrates (55%), fat (20% to 25%), and protein (15% to 20%). Teens who are healthy and eating a good diet do not need nutritional supplements. Eating a high-carbohydrate meal four to six hours before a sports competition can improve performance and well-being.

Don't forget to drink enough water, which is the most important nutrient, making up 60% of the body. During exercise, you should drink ¹/₂ cup to 1 cup of water every 15 to 30 minutes depending on the heat index and the intensity of the exercise.

Avoid "semistarvation" diets—those in which the number of calories you consume during a 24-hour period is more than 500 to 1,000 below the number of calories you burn. Deficits greater than 500 to 1,000 calories usually result in very limited additional loss of fat and promote loss of water and some fat-free tissue (muscle). Most people on such diets tend to regain weight quickly.

Severely reducing the number of calories you take in causes your body to lose large amounts of water, electrolytes (substances such as sodium and potassium), and minerals. In addition, the body looks for sources of energy other than fat and finds it in muscle and glycogen (carbohydrate stored mostly in the liver), which it then uses to produce energy. This undermines strength and endurance.

Get enough exercise

Adequate exercise, along with moderately reducing the number of calories you consume, promotes the most efficient loss of fat while preserving fat-free tissue. The minimum amount of aerobic activity necessary to benefit from this efficient fat loss is 30 minutes three times a week of an exercise that burns about 350 calories in one workout.

Studies suggest that you must burn 3,500 calories to lose one pound of fat. You can therefore lose 1 or 2 lbs of fat a week by burning 500 to 1,000 more calories a day than you take in. (Remember: Burning more than 500 to 1,000 calories beyond what you take in leads to loss of fat-free tissue and is undesirable.)

Maintain your "natural weight"

You should strive to maintain a "natural weight." Natural weight is your weight when you are eating a healthy, balanced diet with enough calories to sustain growth and usual daily activities and getting 30 minutes of aerobic exercise at least three times a week. Your doctor can help you determine your natural weight and body fat composition (what percentage of your weight consists of fat).

For most boys (with some variation), the normal range of body fat composition is 7% to 20%. A body fat composition of 10% to 15% is considered excellent. For most girls (again, with variation), the acceptable body fat range is 12% to 25%. A range of 15% to 20% is ideal. Abnormally high body fat composition can lead to health problems such as high blood pressure, a high cholesterol level, heart disease, diabetes, and gall bladder disease.

Too little body fat, like too much, can be bad for your health. Body fat below 7% for boys can interfere with growth, strength, and endurance. Body fat below 12% for girls can be associated with problems such as missed menstrual periods, weak bones, and eating disorders.

This Guide for Patients may be photocopied and distributed without permission to give to your patients and their parents. Reproduction for any other purpose requires express permission of the publisher. Copyright © 2001 Medical Economics Company.

 

Readers' Forum. Contemporary Pediatrics 2002;1:123.