When it comes to low fat diets - all are not equal!

May 2 2005

New research from the Stanford University School of Medicine re-enforces what Mum always told you, eat those veggies and those other nutrient-dense foods because they're good for you!

In yet more advice on what to eat and what not to eat, researchers have found that a low-fat diet rich in vegetables, fruits, whole grains and beans has twice the cholesterol-lowering power of a conventional low-fat diet, and even when meals contain the same amount of saturated fat and cholesterol a meal of spinach salad, egg and oatmeal-carrot cookies is healthier for your heart than stir-fried lean beef and asparagus and low-fat chocolate chip cookies. It was found that it is not enough to simply steer clear of saturated fat and cholesterol.

In a meticulous comparison of two low-fat diets, the conventional diet, focused solely on avoiding harmful saturated fat and cholesterol and diners ate such foods as frozen waffles and turkey bologna sandwiches, the other diet included the same proportions of fat and cholesterol, plus lots of plant-based foods in accordance with American Heart Association guidelines. Those diners ate such foods as hot grain cereals and vegetable soups.

Both diets lowered total and low-density lipoprotein (LDL, or "bad") cholesterol over the course of the four-week study. The conventional diet produced, on average, a 4.6 percent LDL decrease. But the plant-based diet won hands-down as it achieved, on average, a 9.4 percent decrease in LDL. Researchers found no significant differences in changes in triglycerides or high-density lipoprotein ("good") cholesterol and say that the effect of diet on lowering cholesterol has been minimized and undermined by a lot of clinicians and researchers.

Christopher Gardner, PhD, assistant professor (research) of medicine at the Stanford Prevention Research Center and lead author on the National Institutes of Health-funded study, says many doctors have felt better about putting patients on drugs to control cholesterol and part of the reason was that diets were not given a fair go as the focus was on the negative and what to avoid rather than on what to include.

Gardner says that it is hoped that people will appreciate the new American Heart Association Guidelines, and include more 'whole grains and vegetables and beans and colours, not just iceberg lettuce, but red bell peppers and carrots and broccoli and red cabbage and the really colourful foods in their diet' as they are all really low in saturated fat and cholesterol and very high in other nutrients and phytochemicals.

A "plant-based" diet is not a vegetarian diet but simply includes a basis of whole grains, vegetables, beans, nuts, seeds and fruits. The 2000 AHA guidelines recommend at least five daily servings of vegetables and fruits and at least six daily servings of grains with an emphasis on whole grains.

Gardner says other studies have also shown plant-based diets to be effective in lowering cholesterol.

The interesting aspect of the Stanford study is that it breaks new ground by comparing two patient groups eating different foods but identical amounts of total and saturated fat, protein, carbohydrate and cholesterol. So the two groups' different levels of blood cholesterol change are attributable to the different foods -- dark green salads and bean burritos, for example, versus iceberg lettuce and frozen pizza -- and not differences in saturated fat and cholesterol intake.

The randomized clinical trial included 120 adults, ages 30 to 65 and all were members of the target population for food-based approaches to lowering cholesterol with moderately high LDL levels, between 130 and 190 mg/dL. They were randomly divided into two diners' groups: 61 ate the conventional diet, while 59 ate the plant-based diet. Each weekday for a month, they visited a research dining hall for a specially prepared, carefully weighed, chemically analysed lunch or dinner.

The study required that participants maintain a constant weight so that any changes in blood cholesterol would be attributable to the diets themselves -- not to any changes in weight brought on by the diets. When changes in weight were observed, the participants' calories were changed accordingly to help them stay stable. In general researchers tended to add calories to the meal plan over the course of the study as participants were observed to be more likely to lose weight than to gain weight on both diets.

The scientists also requested that no one change exercise habits, saying: "If you are a marathon runner, keep running marathons. But if you're a couch potato, we need you to stay a couch potato."

Gardner, a 20-year vegetarian who specializes in nutrition and preventive medicine, expects a plant-based diet combined with weight loss and exercise to achieve even more impressive cholesterol-lowering results.

Gardner's research collaborators include Ann Coulston; Lorraine Chatterjee; Alison Rigby, PhD, MPH; Gene Spiller, PhD, and John Farquhar, MD.

Stanford University Medical Center integrates research, medical education and patient care at its three institutions -- Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children's Hospital at Stanford.

The findings are published in the May 3 issue of the Annals of Internal Medicine.