WASHINGTON -- People who want to stay healthy need to exercise for at least an hour a day -- double the previous workout recommendation -- according to new dietary guidelines on fat, protein and carbohydrate intake.

Independent advisers to the government, in a report Thursday, avoided setting strict amounts for each of the three major components, proposing ranges so people can balance their diet.

"The ranges are new and were developed to assure a nutritionally adequate diet," said Joanne R. Lupton of Texas A&M University, head of the Institute of Medicine committee that prepared the study.

The institute, for the first time, added an exercise recommendation to its dietary advice.

"To reduce some of the main killers of America we will have to increase the level of physical activity," said Dr. Benjamin Caballero, director of the Center for Human Nutrition at Johns Hopkins University in Baltimore.

The committee recommended at least one hour of moderate physical activity daily, such as walking, slow swimming, leisurely bicycle riding or golfing without a cart. That's twice the latest government guidance, recommended by the surgeon general in 1996.

Lupton said the committee recognizes that the lifestyles of many people might make this goal seem difficult to achieve. But Caballero noted that the exercise can be broken up and spread throughout the day.

In addition to recommending an hour of exercise daily for adults, the same amount was suggested for youngsters, and comes at a time when worry is increasing over the number of obese children.

Health summit planned

Former Surgeon General David Satcher has organized a national summit of health and education experts next month to discuss ways to trim the fat from young people.

"We based our conclusions on the most scientifically compelling evidence," said Lupton, who teaches nutrition. "We hope this report will guide policy-makers, health professionals and others."

The report was prepared for government agencies that deal with health and nutrition in the United States and Canada. It could eventually lead to changes in food labels and government dietary recommendations.

The institute edged away from previous guidelines that called for getting 50 percent or more of calories from carbohydrates and 30 percent or less from fat.

"We established ranges for fat, carbohydrates and protein because they must be considered together," Lupton said.

The institute, part of the National Academy of Sciences, said that because fats, carbohydrates and protein can all serve as sources of energy they can, to some extent, substitute for one another in providing calories.

The guidelines suggest getting 45 percent to 65 percent of calories from carbohydrates (sugars and starches found in such foods as fruit and bread); 20 percent to 35 percent from fat (meat, dairy products and oils); and 10 percent to 35 percent from protein (available from meat, eggs, dairy products and some vegetables). The protein recommendation is the same as in the past.

Panel members declined to discuss specific diets recommending such things as high fats or low carbohydrates. But they noted the report urges eating at least 130 grams of carbohydrates daily to ensure that the brain has enough glucose to function properly.

Differing diets

"We must distinguish between diets to lose weight and diets to maintain health," Caballero said. He said weight loss diets are temporary and provide less energy intake than needed.

"Our report focuses on diet for the long term to maintain health," he said. For obese people, dieting is not enough, they must also increase their activity level, he said.

Lupton noted that studies have shown that when people eat very low levels of fat and very high levels of carbohydrates their good cholesterol declines. Good cholesterol, or high-density lipoprotein, can reduce the likelihood of heart attack.

On the other hand, she added, high-fat diets can lead to obesity and its health dangers.

The study noted that fat is a major source of energy in the diet, but urged avoiding saturated fats and trans fatty acid as much as possible because they can increase the risk of heart disease.

The main sources of saturated fats are baked goods, meat and full-fat dairy products. Trans-fatty acids are often found in cookies, crackers and meats. The institute recommended this year that trans-fatty acids be listed on food product labels so people can reduce their intake.

For adults under age 50 the report recommends a daily intake of 38 grams of fiber for men and 25 grams for women. Over age 50 the recommendations are 30 grams for men and 21 grams for women. It also urges avoiding added sugars, such as in soft drinks.

The academy is an independent organization chartered by Congress to provide guidance to the government in scientific issues.

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