Posted on 08/13/2012 at 12:43:34 PM by Student BloggerBy Larry Istrail
U.S. News and World Report recently put out an evaluation (1) of the most effective diets for various outcomes, according to these experts. (2) The outcomes varied from weight loss, to the best diet for heart health or diabetes. The "Heart-Health" award was awarded to the ultra-low-fat Ornish Diet.
The summary even states that “if [dieters] use a rigorous version of the plan they could actually reverse heart disease.” This claim - which is ubiquitous in the medical literature - is based on one study on 35 people, deemed the landmark heart disease-reversal trial by the reviewers of this diet assessment.
Twenty of the 35 people were randomized to receive the intervention, which included consuming a low-fat vegetarian diet for at least a year. The diet consisted of fruits, vegetables, grains, legumes, and soybean products without caloric restriction. No animal products were allowed except egg whites and one cup per day of non-fat milk or yogurt; 10% of calories as fat, 15-20% protein, and 70-75% carbs. Cholesterol intake was limited to 5 mg/day.
Subjects also asked to practice stress management techniques at least 1 hour per day, exercise for at least 3 hours exercise per week, and quit smoking if they were smokers. They also attended group meetings two times per week. The control group was given no guidance besides to continue following their own physician's advice.
After one and five years, the experimental group had less cardiac events, and a decrease in the size of the plaques in their coronary arteries.
This is perhaps one the most referenced studies in support of the protective effects of a low-fat diet- cited over 930 times (previous publication cited over 1500) according to Google Scholar, which is unfortunate due to the tremendous amount of confounding interventions. Along with an extremely low fat diet, the experimental group ate more fruits and vegetables, lost 23.9 pounds (control lost no weight), performed relaxation techniques 1 hour each day, exercised at least 3 hours a week, and had group counseling. The control group had none of this. The experimental group contained only 20 subjects (all male), and the control group had 15 (12 men and 3 women).
The small sample size resulted in an uneven distribution of risk factors between groups. At baseline, the mean age of the control group participants was 4 years higher, mean total cholesterol 8% higher and mean LDL 10% higher than those in the experimental group. Mean BMI was three points higher in the experimental group.
The results are great and demonstrate that the sum total of all interventions - vegetarian diet, exercise, smoking cessation, stress management, and group meetings, and weight loss - resulted in a reversal of heart disease. However, it does NOT say that the diet specifically caused all or any of it. This insight simply can't be determined from this study because there were so many interventions.
Despite these extreme limitations to this study, it has been promoted in the media as a panacea, constantly cited as proof that a low-fat, vegetarian diet reverses heart disease. What do you think?