CBS News Medical Correspondent Elizabeth Kaledin reports Americans are still in the Dark Ages when it comes to understanding dieting, but the government has conducted a study as a first step toward clearing that up.
Most popular diets help people drop pounds initially but only traditional moderate-fat, high-carbohydrate regimens seem to keep the weight off, the government concludes.
The U.S. Agriculture Department study found that any diet that limits food to about 1,500 calories per day produces short-term weight loss, but those diets do little to help a dieter lower cholesterol and blood pressure levels.
"In sum, all popular diets, as well as diets recommended by governmental and nongovernmental organizations, result in weight loss. However, it is important to note that weight loss is not the same as weight maintenance," the report said.
The study is to be released Thursday at a meeting at which the department will consider ideas for a long-term study of diet programs. The study will be conducted by the department's network of human nutrition laboratories.
The report is the first from a continuing review of various popular diet programs.
Agriculture Secretary Dan Glickman believes further guidance is needed to help the public sort out the facts about popular diets.
"Here we have people spending billions of dollars of their money and all this effort to look trim and to be healthy, yet we still really don't know what works," said Glickman.
"We need to see which diets sustain weight loss and which diets do it in a way that won't hurt you," he added.
Those weight-loss programs that have put more demands on dieters like those recommended by groups such as the American Heart Association and Weight Watchers have the best scientific evidence to back up their success rates and health claims.
They recommend consuming no more than 30 percent of calories as fat, limiting protein to about 20 percent of the diet and consuming more complex carbohydrates fruits, vegetables and grains to help satisfy hunger with fewer calories.
They are the most nutritionally adequate and showed some of the best improvements in blood levels of the most dangerous cholesterol and blood fats and in blood sugar control, the study found. By comparison, there is weak scientific evidence as to the nutritional adequacy of both the low-carbohydrate and low-fat diet programs, USDA found.
According to the government's latest dietary guidelines, which are revised every five years to reflect the latest developments in science, the best way to control weight is by exercising regularly and eating a balanced diet that includes a lot of whole grains, fruits and vegetables.
Long-term weight control is more related to "psychological issues," such as dietary counsel and group support, than nutrient composition, the report said.
The UDA research "is long overdue, given the problems that the country is facing in terms of obesity," said Cutberto Garza, a professor of nutrition at Cornell University. "Trying to find effective treatment programs is absolutely crucial."
The report is to be published in the March-April issue of the journal Obesity Research.
A spokeswoman for Robert Atkins, a promoter of a popular high-fat, low-carbohydrate diet, agreed that more research is needed but said the government is biased against programs like Atkins'.
"The government is going to go out of their way to prove that their recommendations of the last 20 years are correct. It's the same old story. It's the same-old low-fat propaganda," said Colette Heimowitz, director of education and research for Atkins Health and Medical Information Services.