This study is a retrospective analysis of the records of patients who attended a physician-supervised 10-day residential program (the McDougall Program) from 2002 to 2011. This ongoing program used Internet marketing to attract patients from a wide geographic area to spend 10 days at a hotel in Santa Rosa, California, where they received dietary counseling and were fed a low-fat (≤10% of calories) diet based on minimally refined plant foods ad libitum to satiety. The educational staff included a medical doctor, a registered dietitian, a psychologist, exercise coaches, and cooking instructors. Patients were also given opportunities for light to moderate exercise. No stress reduction techniques or meditations were included in the program.

Medical workup

Upon admission, a standardized questionnaire was used to ask patients if they had any history of hypertension, coronary artery disease, diabetes, hypothyroidism, multiple sclerosis, hypercholesterolemia, or overweight. The patient’s age, sex, and ethnicity were also recorded.

A licensed medical doctor saw all patients on at least 3 occasions during the program, and blood pressure was recorded daily. At baseline, the physician took the patient’s history and performed a physical examination. The physician then recommended appropriate changes to each patient’s medications. Medications for hypertension and diabetes were reduced or discontinued at baseline in order to lessen the risk of hypotension and hypoglycemia. Cholesterol-lowering medications (statins) were continued throughout the program for those people taking this class of medication upon entering the program.

To facilitate analysis, the following data were recorded according to standardized methods at baseline and on day 7: weight, systolic and diastolic blood pressure, total cholesterol, triglycerides, glucose, blood urea nitrogen, and creatinine. After August 2006, HDL and LDL cholesterol were also measured at baseline and day 7. Body weights were measured with a Detecto® 6800 portable bariatric scale. Blood pressure readings were obtained by a trained operator, manually and/or using an Omron® professional sphygmomanometer. Blood tests were analyzed by using standard medical hospital laboratory procedures.

Menu design

The hotel’s kitchen staff prepared foods according to prescribed guidelines. No animal-derived ingredients (e.g, meat, fish, eggs, or dairy products) and no isolated vegetable oils (e.g, olive, corn, safflower, flaxseed, or rapeseed oil) were used. Meals were based around common starches, including wheat flour products, corn, rice, oats, barley, quinoa, potatoes, sweet potatoes, beans, peas, and lentils, with the addition of fresh fruits and non-starchy green, orange, and yellow vegetables. The macronutrient profile was roughly 7% fat, 12% protein, and 81% carbohydrate by calorie. Meals were served buffet-style, and participants were encouraged to eat to the full satisfaction of their appetite.

To ensure that the foods would be acceptable to palates accustomed to Western diets, small amounts of simple sugars, salt, and various spices were used in meal preparation. Sugar was included in condiment sauces (e.g, ketchup and barbecue sauce) and in the low-fat desserts that were served after evening meals. Patients could also add sugar to their cereal in the morning.

The kitchen staff used minimal salt, mostly in the form of soy sauce, when preparing the meals. The basic meal plan provided roughly 1000 mg of sodium per day. However, saltshakers were provided at meals, and participants were allowed to use regular table salt ad libitum on the surface of their foods for taste. We conclude that even if a patient added a total of a half-teaspoon of salt per day, the diet would still qualify as low-sodium (approximately 2 g of sodium daily).

Statistical methods

Data from patients who attended the program from 2002 to 2011 were analyzed in 2014. For patients who attended the program more than once, each visit was regarded as a separate patient record. Records from subjects under the age of 21 were excluded from the analysis. Records with missing data for baseline or day 7 were also excluded.

Before August 2006, tests for HDL and LDL cholesterol were not routinely ordered. Only the records that had baseline and day 7 values were included in the analysis of HDL and LDL. The average total cholesterol values and the change in total cholesterol from day 1 to day 7 for the patients with missing HDL and LDL data were compared to the respective values for the patients with complete data on HDL and LDL.

The change from baseline in biomarkers was analyzed for risk categories based on the patients’ baseline variables. The cutoffs for the risk categories were arbitrary: total cholesterol <150, 150–179, 180–209, 210–239, or ≥240 mg/dL; triglycerides <150, 150–199, 200–499, or ≥500 mg/dL; glucose <100, 100–126, or >126 mg/dL; systolic blood pressure < 140 or ≥140 mm Hg; diastolic blood pressure <90 or ≥90 mm Hg; creatinine <1, 1–1.4, or >1.4 mg/dL; and blood urea nitrogen <10, 10–20, or >20 mg/dL. Because the patients’ height was not recorded, the patients could not be stratified according to body mass index. Instead, they were stratified according to their weight, as expressed in standard deviations from the mean for his or her sex.

Because none of the continuous biomarker variables were normally distributed, Wilcoxon’s signed-rank tests were used to compare baseline values to day 7 values for all biomarker variables. Each comparison was evaluated for the baseline risk categories, as described above. McNemar’s test for paired proportions was conducted to compare the percentage of patients with elevated biomarkers (total cholesterol ≥200 mg/dL, SBP ≥140 mm Hg and DBP ≥90 mm Hg) at baseline whose values fell to normal at day 7 to the percentage of patients with normal biomarkers at baseline whose values were considered elevated at day 7.

In 2013, the American College of Cardiology and American Heart Association published guidelines for estimating a patient’s probability of having a cardiac health event (atherosclerotic cardiovascular disease, ASCVD) within 10 years [15]. The guidelines define high ASCVD as a risk >7.5%. The ASCVD risk can be calculated only for patients whose records include all of the relevant variables: age, total cholesterol, HDL cholesterol, systolic blood pressure, smoking status, diabetes diagnosis, and treatment for high blood pressure. For those patients, the ASCVD risks were calculated twice: once for the baseline values and again for the day 7 values. All of the patients who were on blood pressure medication at baseline were considered to be under treatment for high blood pressure at day 7 as well.

All statistical analyses were conducted by using SAS 9.3 (Cary, NC).