Last week, the federal government released its Dietary Guidelines for Americans 2005. Updated once every five years based on the latest science, the 70-page document purports to tell us which foods are best to eat to stay healthy.

While touted as the strongest nutrition recommendations yet, what went unsaid speaks volumes about why Americans continue to be left in the dark when it comes to eating right. Most media reports focused on the guidelines' emphasis on weight loss, especially the recommendation to exercise daily. But why is a document that's supposed to be about food talking about exercise? Yes, exercise is important to good health, but so are a number of other lifestyle factors, such as sufficient sleep and not smoking, yet those aren't mentioned.

Emphasizing weight loss conveniently puts the onus for dietary change on the individual and avoids talk of reining in the food industry's multibillion- dollar marketing budget for unhealthy foods. "It's just common sense," explained outgoing Health and Human Services Secretary Tommy Thompson. "Eat less, exercise more," he cheerfully instructed Americans.

Stressing weight loss also avoids the much harder job of telling Americans the truth about specifically what not to eat. The government's recommendations only tell part of the story; the politically expedient part.

Under the heading of "Food Groups to Encourage," are fruits, vegetables and whole grains, foods that most Americans desperately need to increase. Trouble is, many of those same Americans don't even know what a whole grain is or where to find one. You can't go to the supermarket and ask for the whole- grain aisle. (Sadly, though, you can ask for the potato-chip aisle or the cookie aisle or the soda aisle.)

Americans have become accustomed to eating highly processed foods that come in a package -- the antithesis of whole foods that come from nature. The very definition of food has been transformed by industry, yet the dietary guidelines don't reflect that. If they did, it would be a major threat to a $500 billion-a-year processed foods industry whose voice is heard loud and clear in Washington.

Responding to that threat, companies such as General Mills are already jumping on the "healthy food" bandwagon, announcing that their products will be reformulated to include whole grains. But "processed whole foods" is an oxymoron. Real whole grains come from nature, such as brown rice instead of Uncle Ben's white rice or plain oatmeal instead of Cheerios with added sugar and salt. Don't let the food industry fool you into thinking it can manufacture healthy foods. That's nature's job.

Another processed-food secret the federal government won't tell you is how to avoid trans fats. In a teleconference last week, Dr. Carlos Camargo of Harvard Medical School and a member of the dietary guidelines committee said he was "disappointed" that the experts' unanimous recommendation to limit trans fats to 1 percent of calories was completely omitted from the final document. Instead, we are told to simply "limit intake" of trans fat.

Why the change? "Food Politics" author and New York University professor Marion Nestle explained in an interview with me: "Trans fat was left vague because otherwise they would have to say where trans fats are -- in processed foods." In wording that Nestle calls "incomprehensible," the consumer-friendly guidelines brochure recommends that you "look for foods low in saturated fats and trans fats" -- the two most common artery-clogging fats in the supermarket.

Why would the government tell you to "look for" foods that you really should avoid altogether? Because Uncle Sam cannot say: Don't eat too many of the major sources of saturated fats: meats, cheese, milk and eggs. Nor could they tell us to avoid the main sources of trans fats: baked goods such as chips, cakes and cookies. That would ruffle too many industry feathers. Keeping the wording as vague as possible is good for big business.

Some nutritionists were understandably pleased with the government's sugar recommendation this time around. That the sugar industry has been complaining so loudly is certainly a good sign. Yet, part of the advice is simply to choose beverages with "little added sugars" -- still pretty fuzzy language.

Americans need is to be told outright: Stop drinking so much Coke. People don't think in terms of ingredients. Most consumers don't even buy ingredients anymore because they don't cook. We think in terms of packaged-food brand names and fast-food menu items. Imagine dietary guidelines that said: Stop eating Big Macs, Doritos and Oreos. Those are recommendations most Americans could understand, but not ones we are likely to hear. Until people are told the entire truth, instead of meaningless messages such as "eat less," the nation's health will continue to suffer.

Michele Simon, a public-health attorney who teaches health policy at UC Hastings College of the Law, directs the Center for Informed Food Choices, a nonprofit in Oakland.

© 2005 San Francisco Chronicle