The new version promotes guidelines announced in January, which emphasize eating fruits and vegetables, going easy on meat and fats, limiting sodium consumption to about 1 teaspoon a day and exercising at least 30 minutes daily to keep from gaining weight.

The guidelines, which are updated every five years, are the basis of U.S. nutrition programs, including food stamps and school lunches.

On the new pyramid, each band of color stands for a food group, and its thickness shows the proportion each group should be in the diet. Orange is for grains; green for vegetables; red, fruits; blue, milk products; purple, meat and beans; and yellow, oils.

The new design also guides people to the USDA's comprehensive health Web site, www.mypyramid.gov, which features 12 pyramids tailored to various nutrition needs. That's an important update of the one-size-fits-all suggestions of the 1992 pyramid, Agriculture Secretary Mike Johanns said.

The new site is interactive, with dietary recommendations based on age, gender and level of physical activity. Consumers can keep online eating diaries through the site, which will measure how their eating habits match up with the federal guidelines.

Johanns said the 1992 pyramid, which included suggested servings for each of its five food groups but didn't lead people beyond that information, was a mixed blessing. It contained more information about foods and serving recommendations than the new one does, but proved to be confusing about how big portions were, and its guidelines often weren't followed.

Eighty percent of Americans recognize the old pyramid, Johanns noted, but 65 percent of Americans are overweight. That pyramid "has become quite familiar, but few Americans follow the recommendations," he said.

Interest in the new site was high its first day, jamming it with more than 1,000 visits a second. USDA officials said transmission problems should be fixed soon, once the traffic dies down a little.

Nutritionist Peter Beyer at the University of Kansas Medical School in Kansas City , Kan., said the Internet-age pyramid offered people a chance to manage their diets better.

"The amount of information available has increased tremendously," he said. Under the old pyramid, "consumers didn't understand servings. They'd think a plate of pasta was a serving," leading to poor choices.

The new pyramid, which the USDA regards as a symbol of healthy living, features explanatory text with its poster and Web site versions, but not within the pyramid itself, unlike the old one. The new guidelines include 23 dietary recommendations and 18 suggestions for older people, children and other special populations, and "If you try to put that on one shape, you're going to miss important things," Beyer said.

The revamped symbol has drawbacks, too, said Tim Radak, the nutrition director for the Physicians Committee for Responsible Medicine in Washington.

Radak said the new dependency on the Internet would frustrate the millions of people who lacked access to it. They tend to be lower-income or elderly, he added, two groups with high rates of obesity.

The pyramid also can make inappropriate recommendations for certain ethnic groups and people with special dietary needs. About 50 million Americans - mostly black, Hispanic and Asian-American - are lactose-intolerant, making the blue "milk" ray of the pyramid impossible to follow.

"It's discriminatory to mandate guidelines that certain groups can't follow," said Radak, whose group advocates plant-based, low-dairy diets.

Eric Hentges , the director of the Agriculture Department's Center for Nutrition Policy and Promotion, said the USDA would reveal more pyramid options in coming months, including nutrition plans for different ethnic groups. The site also includes tips for healthy vegetarian diets, he said.