Research shows that plant-based diets are cost-effective, low-risk interventions that may lower body mass index, blood pressure, HbA1C, and cholesterol levels. They may also reduce the number of medications needed to treat chronic diseases and lower ischemic heart disease mortality rates. Physicians should consider recommending a plant-based diet to all their patients, especially those with high blood pressure, diabetes, cardiovascular disease, or obesity.
In the HBO documentary The Weight of the Nation, it was noted that if you “go with the flow” in the US, you will eventually become obese.
In 2011, Witters reported that in some areas of the country, the rate of obesity is 39% and is increasing at a rate of 5% per year.
Risks of obesity, diabetes, hypertension, and cardiovascular disease, along with their ensuing complications (eg, behavioral health and quality-of-life problems) often go hand-in-hand and are strongly linked to lifestyle, especially dietary choices.3 Of all the diets recommended over the last few decades to turn the tide of these chronic illnesses, the best but perhaps least common may be those that are plant based.
Despite the strong body of evidence favoring plant-based diets, including studies showing a willingness of the general public to embrace them,4 many physicians are not stressing the importance of plant-based diets as a first-line treatment for chronic illnesses. This could be because of a lack of awareness of these diets or a lack of patient education resources.
National dietary guidelines for active living and healthful eating are available at http://www.ChooseMyPlate.gov.5 A typical healthful plate of food is 1/2 plant foods (nonstarchy vegetables and fruits), 1/4 whole grains or unprocessed starchy food, and 1/4 lean protein.
The goal of this article is to review the evidence supporting plant-based diets and to provide a guideline for presenting them to patients. We start with a case study and conclude with a review of the literature.
Case Study
A 63-year-old man with a history of hypertension presented to his primary care physician with complaints of fatigue, nausea, and muscle cramps. The result of a random blood glucose test was 524 mg/dL, and HbA1C was 11.1%. Type 2 diabetes was diagnosed. His total cholesterol was 283 mg/dL, blood pressure was 132/66 mmHg, and body mass index (BMI) was 25 kg/m2. He was taking lisinopril, 40 mg daily; hydrochlorothiazide, 50 mg daily; amlodipine, 5 mg daily; and atorvastatin, 20 mg daily. He was prescribed metformin, 1000 mg twice daily; glipizide, 5 mg daily; and 10 units of neutral protamine Hagedom insulin at bedtime. His physician also prescribed a low-sodium, plant-based diet that excluded all animal products and refined sugars and limited bread, rice, potatoes, and tortillas to a single daily serving. He was advised to consume unlimited non-starchy vegetables, legumes, and beans, in addition to up to 2 ounces of nuts and seeds daily. He was also asked to begin exercising 15 minutes twice a day.
The patient was seen monthly in his primary care clinic. Over a 16-week period, significant improvement in biometric outcome measures was observed. He was completely weaned off of amlodipine, hydrochlorothiazide, glipizide, and neutral protamine Hagedorn insulin. Follow-up blood pressure remained below 125/60 mmHg, HbA1C improved to 6.3%, and total cholesterol improved to 138 mg/dL. Lisinopril was gradually decreased to 5 mg daily and his diabetes is controlled with metformin alone, 1000 mg twice daily.
Definitions of Plant-Based Diets
The presented case is a dramatic example of the effect a plant-based diet can have on biometric outcomes like blood pressure, diabetes, and lipid profile. The reduction in HbA1C from 11.1% to 6.3% in 3 months is much better than would be expected with monotherapy with metformin6 or daily exercise.7 The improvement in blood pressure observed over a 4-month period with few medications is also rarely encountered in clinical practice and is likely related to a low-sodium diet and the avoidance of red meat. Because the patient was not obese and did not have significant weight loss with the diet, the dramatic improvements appear to be related to the quality of his new diet.
A healthy, plant-based diet aims to maximize consumption of nutrient-dense plant foods while minimizing processed foods, oils, and animal foods (including dairy products and eggs). It encourages lots of vegetables (cooked or raw), fruits, beans, peas, lentils, soybeans, seeds, and nuts (in smaller amounts) and is generally low fat.8,9 Leading proponents in the field have varying opinions as to what comprises the optimal plant-based diet. Ornish et al recommends allowing animal products such as egg whites and skim milk in small amounts for reversal of disease.10,11
Esselstyn, who directs the cardiovascular prevention and reversal program at the Cleveland Clinic Wellness Institute, recommends completely avoiding all animal-based products as well as soybeans and nuts, particularly if severe coronary artery disease is present.
Despite these smaller differences, there is evidence that a broadly defined plant-based diet has significant health benefits. It should be noted that the term plant-based is sometimes used interchangeably with vegetarian or vegan. Vegetarian or vegan diets adopted for ethical or religious reasons may or may not be healthy. It is thus important to know the specific definitions of related diets and to ascertain the details of a patient’s diet rather than making assumptions about how healthy it is. The following is a brief summary of typical diets that restrict animal products. A key distinction is that although most of these diets are defined by what they exclude, the plant-based diet is defined by what it includes.
- Vegan (or total vegetarian): Excludes all animal products, especially meat, seafood, poultry, eggs, and dairy products. Does not require consumption of whole foods or restrict fat or refined sugar.
- Raw food, vegan: Same exclusions as veganism as well as the exclusion of all foods cooked at temperatures greater than 118°F.
- Lacto-vegetarian: Excludes eggs, meat, seafood, and poultry and includes milk products.
- Ovo-vegetarian: Excludes meat, seafood, poultry, and dairy products and includes eggs.
- Lacto-ovo vegetarian: Excludes meat, seafood, and poultry and includes eggs and dairy products.
- Mediterranean: Similar to whole-foods, plant-based diet but allows small amounts of chicken, dairy products, eggs, and red meat once or twice per month. Fish and olive oil are encouraged. Fat is not restricted.
- Whole-foods, plant-based, low-fat: Encourages plant foods in their whole form, especially vegetables, fruits, legumes, and seeds and nuts (in smaller amounts). For maximal health benefits this diet limits animal products. Total fat is generally restricted.
Benefits of Plant-Based Diets
The goal of our diet should be to improve our health. In this section, we will review the literature for key articles that demonstrate the benefits of plant-based diets. Our review consists of existing studies that include vegan, vegetarian, and Mediterranean diets.
Obesity
In 2006, after reviewing data from 87 published studies, authors Berkow and Barnard13 reported in Nutrition Reviews that a vegan or vegetarian diet is highly effective for weight loss. They also found that vegetarian populations have lower rates of heart disease, high blood pressure, diabetes, and obesity. In addition, their review suggests that weight loss in vegetarians is not dependent on exercise and occurs at a rate of approximately 1 pound per week. The authors further stated that a vegan diet caused more calories to be burned after meals, in contrast to nonvegan diets which may cause fewer calories to be burned because food is being stored as fat.