Vitamin, calcium and fiber supplements that Americans consume by the millions of doses are useless and potentially harmful, says a report Wednesday by the National Research Council.

The massive NRC study called "Diet and Health: Implications for Reducing Chronic Disease Risk" recommends that higher-than-needed doses of vitamins be avoided and says that neither fiber nor calcium supplements have any value to health.Instead, the 1,300-page report said, people should eat a variety of foods that provide nutrients naturally. Particular attention should be paid to reducing dietary fat, alcohol consumption and salt intake, it said.

The findings on dietary supplements come at a time when Americans are spending millions of dollars on vitamin pills, calcium powders and capsules, and on high fiber compounds.

On vitamins, the NRC study said a good health recommendation is to "avoid taking dietary supplements in excess of the RDA (recommended daily allowance) in any one day."

A daily dose of multiple vitamins with 100 percent of the RDA "is not known to be harmful or beneficial," the report said. "However, vitamin-mineral supplements that exceed the RDA and other supplements (such as protein powders, single amino acids, fiber and lecithin) not only have no known health benefits . . . but their use may be detrimental to health."

Though the study recommended foods high in calcium, it noted that "the potential benefits of calcium intakes above the RDAs to prevent osteoporosis or hypertension are not well documented and do not justify the use of calcium supplements."

Dietary fiber, the study said, could be acquired by eating fruits and vegetables. "Fruits and vegetables contain high levels of fiber, but there is no conclusive evidence that the dietary fiber itself" is a protection against cancers of the stomach, intestine or lungs, the study said.

Healthful diets should include five or more servings of fruit and vegetables daily, and six or more servings of breads, cereals and legumes.

On fermented beverages, the report was blunt: "The committee does not recommend alcohol consumption."

The study said pregnant women should avoid alcohol, and those who do drink should limit their intake to one ounce of alcohol a day, equivalent to two cans of beer, two glasses of wine, or two average cocktails.

Salt should be limited to 6 grams a day for the general population, and there could be health benefits from reducing its use even further, the report said.

The American diet rich in animal fats, however, came under the heaviest attack by the committee.

It recommended that fat be reduced to 30 percent of the calories consumed daily, and that cholesterol consumption be less than 30 milligrams daily.

High fat diets, the study said, are linked to heart disease, cancer and obesity. This echoed findings reported earlier in studies.

The National Research Council is the principal operating agency of the National Academy of Sciences.