This article is part of a series with important health information for teenagers.

You've heard it all before. For as long as you can remember, your parents, your teachers, perhaps even your doctor, have been telling you to eat your vegetables, limit sweets, drink your milk.

Now, in your teen years, this advice takes on new meaning for a lot of very different reasons: How can you gain weight to put on muscle instead of fat? What's a healthy weight for you? How can you squeeze in a good, quick meal after school and before you have to be at your part-time job? All good questions, and because of the enormous changes that are going on in your body, the way you decide to deal with your nutrition needs now can make a big difference not only in how you feel today, but also in your well-being in years to come.

If you are between 15 and 18, you're completing your final major growth spurt, and are in the process of putting on nature's finishing touches for adulthood. For girls, the finishing touch means adding some fat padding. For boys, it means adding muscle and increasing the volume of blood. These changes often encourage girls to diet unnecessarily to stay slim, while boys may overeat to satisfy their appetites. Both can lead to health problems down the road, and, incidentally, probably will not do the job you want right now.

So what is the right approach to healthy eating?

A good start is to eat a variety of foods, as suggested in the Dietary Guidelines for Americans, published by the U.S. departments of Agriculture and Health and Human Services. Get the many nutrients your body needs by choosing a variety of foods from each of these groups:

• vegetables
• fruits
• breads, cereals, rice, and pasta
• milk, yogurt and cheese
• meat, poultry, fish, dried beans and peas, eggs, and nuts.

The pace for teens is fast and getting faster. Added to pressures from school to prepare for college or a job, many teens take part in sports and work part-time. This often means eating on the run. Stack that on top of the snack foods you eat on dates or when you get together with friends, and the balance of your nutrients can get way out of kilter.

Many snacks, such as potato chips, fast-food cheeseburgers, and fries, have high levels of fat, sugar or salt--ingredients that are usually best limited to a small portion of your diet. Healthy eating doesn't mean that you can't have your favorite foods, but the Dietary Guidelines advise you to be selective and limit the total fat, saturated fat, cholesterol, and sodium you eat. Our main source of saturated fat comes from animal products and hydrogenated vegetable oils, with tropical oils--coconut and palm--providing smaller amounts. Only animal fat provides cholesterol. Sodium mostly comes from salt added to foods during processing, home preparation, or at the table.

Fats are our most concentrated source of energy. Scientists know that eating too much fat, especially saturated fat and cholesterol, increases blood cholesterol levels, and therefore increases your risk of heart disease. Too much fat also may lead to overweight and increase your risk of some cancers.

Dietitians recommend that no more than 30 percent of your calories come from fats, and not more than 10 percent of these calories should be from saturated fat. Choose lean meats, fish, poultry without skin, and low-fat dairy products whenever you can. When you eat out, particularly at fast-food restaurants, look for broiled or baked rather than fried foods. Try the salad bars more often, but pass up creamy items and limit the amount of salad dressing you use to keep down the fat and calories. Look for milk-based high-calcium foods with reduced fat.

Spare the Sugar and Salt

Most people like the taste of table sugar. But did you know that other sweeteners are sometimes "hidden" in foods? There are sugars in honey, dried fruits, concentrated fruit juices, and ingredients such as corn syrup that are added to soft drinks, cookies, and many other processed foods. You can see what sugars are in packaged foods by looking at the ingredient list.

If you are a very active teen with high-energy needs, sweets can be an additional source of calories. But keep in mind that they contain only limited nutrients and that both sugars and starches can contribute to tooth decay.

A moderate amount of sodium in your diet is necessary, because sodium, along with potassium, maintains the water balance in your body. But for some people, too much sodium can be a factor in high blood pressure. Since processed foods often contain large amounts of sodium, it's wise to use salt sparingly when cooking or at the table--and to avoid overeating salty snacks like pretzels and chips.

When you exercise heavily and sweat profusely, you can deplete your sodium reserve, unbalance your body chemistry, and possibly become dehydrated. In extreme cases of profuse sweating, such as during training or competition, a dilute glucose-electrolyte drink may become necessary, but always with an abundance of water to make up for sweat losses.

What's All This About Fiber?

Whole-grain breads and cereals, dried beans and peas, vegetables, and fruits contain various types of dietary fiber essential for proper bowel function. Eating plenty of these fiber-rich foods may reduce your risk of cancer and heart disease.

The benefits from a high-fiber diet may be related to the foods themselves and not to fiber alone. For this reason, it's best to get fiber from foods rather than from the fiber supplements you can purchase in a store.

Be Aware of Alcohol

Alcoholic beverages deserve special mention. Drinking them risks good health and can cause other serious problems for teens. And although it is illegal for teens to buy alcoholic beverages, a 1994 survey conducted by the Department of Health and Human Services shows that 31 percent of high-school seniors and 20 percent of juniors reported being drunk in the past 30 days.

Teens who drink risk impaired judgment in their social relationships and endanger their own and others' lives if they drive after drinking. According to the U.S. Department of Transportation, in 1996, 37 percent of fatal crashes involving 15- to 20-year-old drivers were alcohol-related

Alcoholic beverages contain calories but few if any nutrients. Drinking heavily can lead to poor nutrition if alcoholic beverages replace foods with needed nutrients, and alcoholism is not unknown among teenagers.

What About Vegetarians?

There are many types of vegetarian diets, but the two most common are the lacto-ovo, which includes eggs and milk products but not meat, and vegan, which eliminates all forms of animal products. Teens who are lacto-ovo vegetarians can usually get enough nutrients in their diets.

Vegan vegetarians are vulnerable to deficiencies of several nutrients, particularly vitamins D and B-12, calcium, iron, zinc, and perhaps other trace elements. Like all essential nutrients, these vitamins and minerals are required to maintain proper growth.

If it is important to you to be a vegetarian, it is easier to achieve good nutrition with the lacto-ovo form. A dietitian (or your school nurse) can help you plan a vegetarian diet that provides you with the nutrients you need for growth and development during the teen years.

Iron and Calcium

The need for iron for both boys and girls increases between the ages of 11 and 18. The National Academy of Sciences recommends teenage boys get 12 milligrams of iron a day, mostly to sustain their rapidly enlarging body mass. For girls, the recommended daily requirement is 15 milligrams to offset menstrual losses that begin during this time.

It's important to plan how to get adequate iron in your diet. Iron from meat, poultry and fish is better absorbed by your body than the iron from plant sources. However, the absorption of iron from plants is improved by eating fruit or drinking juice that contains vitamin C with the iron-rich food.

Teens need extra calcium to store up an optimal amount of bone (called "peak" bone mass). The richest sources of calcium are milk and other dairy products. Building optimal bone mass through a balanced diet, including adequate calcium, may help delay the onset or limit your chances of developing osteoporosis later in life. Osteoporosis is a disease in which reduced bone mass causes bones to break easily. It occurs in both men and women, but is more common among older women.

What's a Healthy Weight?

Some teens have a difficult time projecting a healthy weight for themselves. Girls especially may think they need to be thinner than they are, or should be. Extraordinary concern or obsession for thinness leads some teens to the eating disorders of anorexia nervosa (dieting to starvation) or bulimia (overeating and then vomiting).

If you're concerned about your weight, it's important to talk to a health professional such as your family doctor or the school nurse. That person can help you decide whether you do need to lose weight and, if so, the best way to achieve and maintain a weight that is healthy for you.

If health professionals recommend that you need to lose weight, most experts say it's best to increase your exercise as the first step. Often that's all teens need to do for weight control because they're rapidly growing. If eating less is also necessary, it is best to continue eating a variety of foods while cutting down on fats and sugars.

Losing weight quickly on a very-low-calorie diet is never a good idea for anyone. And if you're into sports, you should be aware that it could affect your athletic performance. Under no circumstances should you drink less fluid to lose weight. A steady loss of a pound or so a week until you reach your goal is generally safe, and you're more likely to be able to maintain your weight loss.

Skipping meals to lose weight is another poor idea. You're likely to overeat at the next meal just because you're so hungry. And surveys show that people who skip breakfast or other meals tend to have poorer nutrition than those who don't.

Help for Healthy Eating

The food label can help nutrition-conscious people make wise food choices. This can be important to teens who sometimes shop not only for themselves but also for the whole family.

The Nutrition Labeling and Education Act of 1990, enforced by FDA, requires almost all food products to be labeled with the nutritive values they contain per serving. Serving sizes now are more uniform across all product lines, so that you can more easily compare the nutritional values of similar foods; for example, ice cream and frozen yogurt. And the serving sizes are closer to amounts people really eat.

Also, the government has set strict definitions for claims like "low fat" and "light," so when you see them, you can believe them.

FDA now allows food labels to carry claims about the relationship between a food or nutrient and a disease or health-related condition; for example, calcium and a reduced risk of osteoporosis, a bone disease; and sodium and an increased risk of high blood pressure. So far, FDA has approved 10 claims, which are supported by significant scientific evidence.

Thanks to the growing scientific knowledge about diet and health relationships, healthy eating is more socially "in" than ever before. Eating a healthy diet is not difficult with knowledge of a few of the basics and can help you excel on the playing field, in school and in your social life.

Judith Foulke is a member of FDA's Public Affairs Staff.

Dietary Guidelines for All Americans

What should Americans eat to stay healthy? These guidelines, published by the U.S. departments of Agriculture and Health and Human Services, reflect recommendations of nutrition authorities who agree that enough is known about the effect of diet on health to encourage certain dietary practices. The guidelines are:

• Eat a variety of foods.
• Balance the food you eat with physical activity - maintain a healthy weight.
• Choose a diet with plenty of grain products, vegetables and fruits.
• Choose a diet low in fat, saturated fat, and cholesterol.
• Choose a diet moderate in sugars.
• Choose a diet moderate in salt and sodium.
• Children and adolescents should not drink alcoholic beverages.

* Teenagers should have three or more servings daily of foods rich in calcium.

Publication No. (FDA) 99-2257