DR. WALLACE: I am a girls' physical education teacher in Chicago and I'm shocked at the number of my students who are grossly overweight. I've been a P.E. teacher for over 30 years and when I first started teaching, the majority of my students were of normal weight. I'd like your opinion on why today's teens are downright fat. — Teacher, Chicago, Illinois.

TEACHER: Because of their rapid growth and fast-paced lifestyle, most teens should not be overweight, even if they consume a lot of junk food.

The Centers for Disease Control and Prevention reported that, in the 1950s, less than 10 percent of the nation's teens were overweight. By the '70s, the percentage had jumped to 15 percent and by the '90s it was 21 percent. Now it's over 25 percent.

Most of the blame, according to the CDC, lies with the increasingly sedentary lifestyle too many teens lead, which includes lack of exercise and too much time slumped inertly in front of the television or computer screen. Too much junk food, of course, compounds the problem, and current fashion — often baggy, figure-concealing grunge clothing — hides it.

Furthermore, many teens are spending more time indoors than they used to because the streets are unsafe. And since in many families both parents work, the children can eat or snack without parental supervision.

To combat this problem, the Department of Agriculture has lowered the amount of salt and fat allowed in school lunches. This is a positive action, but it won't solve the problem. Teens themselves must learn to eat well-balanced, nutritional meals and exercise regularly. Overweight teens become overweight adults and run a higher risk of heart disease, diabetes and arthritis.

Physical education is a very important program in our schools, and I'm sorry that some school districts eliminate P.E. as a way of saving money.

WAIT BEFORE YOU JOIN THE NAVY

DR. WALLACE: I will graduate from high school soon and I want to join the Navy. I know I'll have to take a physical examination and I know I'll pass because I'm in excellent shape. My only concern is that I have been smoking a little pot lately and I'm told that pot can be detected in your body for a certain length of time. Is this true and if it is, how long do the traces of pot hang around? - Nameless, Santa Ana, California.

NAMELESS: It takes between five and eight days for most of the main ingredient found in marijuana to be eliminated from the body and up to six weeks before it is eliminated completely. Alcohol can be eliminated at the rate of one drink per hour because it's water soluble, but marijuana is fat soluble. The ingredients merge with the fatty tissues and take extra time to be expelled from the body.

To be 100 percent sure that you will pass your physical examination regarding drugs, stop using marijuana immediately and wait two months before you visit the Navy enlistment office.

SKINNY DUCKLINGS BECOME BEAUTIFUL SWANS

DR. WALLACE: I'm a 13-year-old girl who needs help, and fast. I'm tall for my age and I have a slender body. I take after my father, who is tall and skinny, and I don't like it one bit. I want to gain weight on my legs. I've tried eating a lot of junk food, but my legs still look like toothpicks. Help! — Nameless, Reno, Nev.

NAMELESS: There is no way you can add or lose weight in a certain area of the body. You gain or lose weight over your entire body. The best you can do is to eat nutritious, well-balanced meals, and get sufficient rest and proper exercise. Eventually you will come to appreciate being blessed with a tall, slender build, and realize how many women are envious of it. The skinny "duckling" that you believe yourself to be now will turn into a beautiful swan. I guarantee it.

Dr. Robert Wallace welcomes questions from readers. Although he is unable to reply to all of them individually, he will answer as many as possible in this column. Email him at [email protected]. To find out more about Dr. Robert Wallace and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.