Los Angeles, CA - A plant-based low-fat diet helps lower LDL- and total-cholesterol levels to a greater extent than an equivalent low-fat diet based more on convenience foods, a new study has shown.[1]

The results confirm that the revised 2000 American Heart Association dietary guidelines—which emphasize including more plant-based foods while simultaneously limiting saturated fat and cholesterol—are more effective than the previous version of the guidelines, say Dr Christopher D Gardner (Stanford University Medical School, CA) and colleagues in their paper in the May 3, 2005 issue of the Annals of Internal Medicine.

In an accompanying editorial, Dr David JA Jenkins, Dr Cyril WC Kendall, and Augustine Marchie (St Michael's Hospital and University of Toronto, ON) say the paper by Gardner et al "is an important reminder that diet, in addition to drugs, can play a role in achieving cholesterol targets. The most obvious significance of [their paper] is the injection of new enthusiasm into the dietary management of hyperlipidemia."[2]

Gardner et al included 120 people in their study who were moderately hypercholesterolemic (LDL between 3.3 mmol/L and 4.8 mmol/L), aged 30 to 65, whose body mass indexes were less than 31 kg/m². They were assigned to either the low-fat diet or the low-fat-plus diet. The two diets were designed to be identical in total fat, saturated fat, protein, carbohydrate, and cholesterol content.

While the low-fat diet was relatively typical of a low-fat US diet and contained several reduced-fat prepared foods—such as low-fat cheeses, low-fat frozen lasagna, and high-sugar snack foods—the low-fat-plus diet contained considerably more vegetables, legumes, whole grains, and fruits. The diets were followed for four weeks, with all the foods provided by the research team except for one weekly "free-choice" meal.

After four weeks, those following the low-fat-plus diet had a 9.3% total reduction in LDL cholesterol from baseline, compared with a 4.6% reduction in those on the low-fat diet. The two groups did not differ significantly in HDL cholesterol and triglyceride levels.

"We observed a significantly greater reduction in total and LDL cholesterol among moderately hypercholesterolemic men and women who consumed the plant-based low-fat diet compared with those who consumed the more convenience-food-based low-fat diet," the researchers say. "This differential effect is probably attributable to at least one and probably a combination of the components that differed in the two diets, such as the higher content of soy, fiber, garlic, and plant sterols in the low-fat-plus diet."

Gardner told heartwire: "The simple sound-bite that cardiologists were given for so many years probably focuses too much on what to avoid, [but] a larger effect can be obtained by focusing attention on what to include. This is a paradigm shift that has taken place in the AHA's 2000 revision of their dietary guidelines. The goal is more veggies, whole grains, beans, nuts, seeds, and fruits, and the practical way to include them is in the menus of various cultures that have thrived for years on plant-based diets: Asian, Mediterranean, Middle Eastern, and Latin American."

The editorialists say that the findings of the study are not unexpected, since it has been shown before that vegans and vegetarians have lower levels of LDL cholesterol than people who eat a typical diet.

Nevertheless, the 9.3% reduction in LDL seen in those following the plant-based diet "is large enough that we would expect it to reduce all-cause mortality if sustained over time," they observe. The diet thus "occupies an intermediate, bridging position between conventional diets low in saturated fat (which achieve a 5% reduction in LDL-cholesterol level) and drug therapy (which achieves a 25% to 35% reduction in LDL-cholesterol level)."

"The success of diets that combine food containing active cholesterol-lowering components may make diet relevant in the age of powerful drugs like statins," they say.

The authors note that there are a number of strengths and limitations to their study; one of the latter is that it was of short duration. The editorialists say this is one of the problems with diets in general and that the "unanswered question regarding plant-based diets enriched with cholesterol-lowering components is the extent to which they reduce cardiovascular disease." The major barrier to testing this hypothesis is sustained adherence to the diet, "a question that short-term studies do not answer."

However, they add, "Plant-based diets . . . may have benefits other than cholesterol reduction, such as effects on CRP and, in the case of the high-fiber components, satiety and colonic health." Gardner et al also point this out, noting that a plant-based diet is consistent with the dietary recommendations of the American Cancer Society.