Eating a low-fat diet packed with vegetables, fruit, beans and whole grains reduces levels of "bad" cholesterol twice as much as eating a low-fat diet that's heavy on processed foods, a small study has found.

Researchers said it suggests that — at least in the short term — there's more to healthy eating than counting fat grams and more to controlling cholesterol than taking drugs.

"The effect of diet on lowering cholesterol has been really minimized and undermined by a lot of clinicians and researchers saying, 'Yes, it has an effect but it's really trivial. It would be better to put you on drugs to control your cholesterol,'" said Christopher Gardner, lead author of the study in a recent issue of Annals of Internal Medicine.

"But we think part of the reason was that we weren't really giving diet a fair shake. We were so focused on the negative — just what to avoid and not what to include," said Gardner, director of nutrition studies at Stanford University's Prevention Research Center.

The study involved 120 adults and lasted four weeks. The group was divided in half and put on two different low-fat, weight-maintenance diets that had identical total fat, saturated fat, protein, carbohydrate and cholesterol content. The volunteers were not allowed to change their usual amount of exercise and their weight stayed the same.

Half the test group followed a diet with large quantities of plant-based foods — vegetables, fruits, legumes, soy and whole grains — and limited amounts of meat and dairy.

The other half followed a diet that included packaged foods like reduced-fat cheeses, lunch meat, frozen dinners, diet soda and fat-free cookies. Researchers described it as a more typical low-fat diet for U.S. consumers.

After a month, the plant-based diet group's bad cholesterol dropped 9.4 percent, compared to the prepared-foods diet group's reductions of about 4.6 percent.

Earlier studies have shown that plant-based diets can lower cholesterol, Gardner said. But plant-based eaters generally consume less saturated fat and cholesterol than conventional low-fat eaters, and researchers wanted to see what happened when the fat and cholesterol levels were the same for both diets.

After one month, the people who ate the diet that was heavy on plant-based foods saw bigger improvements in levels of LDL, or "bad" cholesterol, than the people who ate processed dinners and snacks.

Gardner was disappointed to discover that levels of triglycerides, another fat that contributes to heart disease, were essentially the same in both groups after four weeks. The reason is unclear, but exercise levels or the study's length might be a factor, he said.

In an accompanying editorial, a nutritionist not connected with the research said plant-based diets, which appear to have many benefits like reduced risks of colon and heart disease, should remain a key strategy for improving cholesterol.

"The success of diets that combine foods containing cholesterol-lowering components may make diet relevant in the age of powerful drugs like statins," said Dr. David J.A. Jenkins of the University of Toronto's Clinical Nutrition and Risk Factor Modification Center.