Effects of 7 days on an ad libitum low-fat vegan diet: the McDougall Program cohort

Background: Epidemiologic evidence, reinforced by clinical and laboratory studies, shows that the rich Western diet is the major underlying cause of death and disability (eg, from cardiovascular disease and type 2 diabetes) in Western industrialized societies. The objective of this study is to document the effects that eating a low-fat (<=10% of calories), high-carbohydrate (~80% of calories), moderate-sodium, purely plant-based diet ad libitum for 7 days can have on the biomarkers of cardiovascular disease and type 2 diabetes.

Methods: Retrospective analysis of measurements of weight, blood pressure, blood sugar, and blood lipids and estimation of cardiovascular disease risk at baseline and day 7 from 1615 participants in a 10-day residential dietary intervention program from 2002 to 2011. Wilcoxon's signed-rank test was used for testing the significance of changes from baseline.

Results: The median (interquartile range, IQR) weight loss was 1.4 (1.8) kg (p < .001). The median (IQR) decrease in total cholesterol was 22 (29) mg/dL (p < .001). Even though most antihypertensive and antihyperglycemic medications were reduced or discontinued at baseline, systolic blood pressure decreased by a median (IQR) of 8 (18) mm Hg (p < .001), diastolic blood pressure by a median (IQR) of 4 (10) mm Hg (p < .001), and blood glucose by a median (IQR) of 3 (11) mg/dL (p < .001). For patients whose risk of a cardiovascular event within 10 years was >7.5% at baseline, the risk dropped to 5.5% (>27%) at day 7 (p < .001).

Conclusions: A low-fat, starch-based, vegan diet eaten ad libitum for 7 days results in significant favorable changes in commonly tested biomarkers that are used to predict future risks for cardiovascular disease and metabolic diseases.

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Alex’s Notes: What happens when you get an author of several books on the role of diet for the prevention and management of chronic disease to fund a study? You get a retrospective analysis of the patient records of persons who attended the 10-day McDougall Program from 2002-2011, where they were fed a low-fat vegan diet and opportunity to exercise. Unfortunately, John McDougall had full access to all the study data, and bias is extremely likely, but the results are interesting nonetheless.

First, however, some amusement. McDougall clearly states in the introduction that “The burden of Western disease can be dramatically reduced by eliminating animal-source foods and vegetable fats from the diet and replacing those foods with low-fat, plant-based foods,” which of course he offers no citations or evidence for. Soon after, he goes on to claim that benefits of reduced mortality can be achieved by having patients “eat a low-fat (≤10% of calories), high-fiber, high-carbohydrate (~80% of calories), purely plant-based (vegan) diet.” This time he offers seven references, of which six were confounded with exercise and lifestyle changes, and the remaining was basically a carbohydrate starvation study even more extreme than the McDougall diet, in which subjects consumed “not more than 5 Gm. of fat and about 20 Gm. of protein derived from rice and fruit” per 2,000 kcal consumed.

Okay, with that solid backing of the McDougall out of the way (sarcasm), let’s look at the actual study. In addition to what was already mentioned, all foods were prepared by hotel staff, with no animal-based ingredients or isolated vegetable oils, and meals were based around common starches such as wheat flour products, corn, rice, oats, barley, quinoa, potatoes, sweet potatoes, beans, peas, and lentils, in addition to fruit and non-starchy fibrous vegetables. Every day was a buffet in which participants could eat to satiety and the overall meal macronutrient composition was approximately 7% fat, 12% protein, and 81% carbohydrate. Minimal salt was used by the kitchen staff in food preparation, but participants could salt to taste via regular table salt. The basic meal plan provided about 1,000mg of sodium.

A total of 1645 subject records were included in the analysis, with 65% being female, 92% being white, and the average age being 58-years. Nearly 40% had self-reported hypertension, 25% hypothyroidism, 64% hypercholesterolemia, and 71% were overweight. Additionally, a third were on blood pressure medication, 22% on statins, and 12% on diabetic medication.

Impressively, after a mere seven days, the average weight loss was 1.4 kg (3 lbs), reductions in total cholesterol were -22 mg/dL, LDL-C was -16 mg/dL, systolic blood pressure was -8 mmHg, diastolic blood pressure was -4 mmHg, fasting glucose was -3 mg/dL. HDL-C was also reduced by 8 mg/dL, but McDougall forgot to mention this in the results section. Additionally, as would be expected, the health improvements were more significant and of greater magnitude in those persons who were at a higher risk at baseline. For example, overall the diet had no effect on triglyceride levels, but it did have a significant effect on participants who began the diet with levels over 500 mg/dL, reducing their blood lipid levels by an average of 294 mg/dL. Finally, a surprising 86.5% of patients on blood pressure medications and 90.7% of patients on diabetes medications reduced their dosage or discontinued the medication entirely. Although, there is no mention of if this was the result of health improvement or simply the persons “felt” like they no longer needed it.

In the discussion, McDougall rightly claims that “This kind of dramatic, early success can be important for maintaining patients’ motivation to adhere to the diet.” Unfortunately, most the participants were overweight and the significant weight loss experienced is a major confounding variable. Moreover, did McDougall forget about the fact that he had his participants exercise? That can kind of make a big difference. Not to mention that the timeframe was too short to see if the improvements would actually be maintained, or even if this type of diet is sustainable.

So while a low-fat vegan diet (coupled with exercise and weight-loss) does indeed improve cardiovascular risk markers by removing a main cause of Western disease: the Western diet, any dietary change that eliminates the host of crap food consumed by Westerners would have this effect. Such is the Paleolithic diet, the Mediterranean diet, etc. And let’s not forget about the ultimate animal-based source of protein and fat – dairy.


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