Is a Plant-Based Diet Right for Your Patient?
ABSTRACT: Switching to a plant-based diet is an effective strategy to reduce obesity and cardiovascular-related risk factors. This article will review the benefits of plant-based diets on all-cause mortality and common chronic diseases, as well as the potential nutritional deficits in protein, vitamins, minerals, and fatty acids. The goal is to provide primary care providers with the tools to discuss ways to improve fruit and vegetable consumption with patients, and how to reduce the harm from potential vitamin and mineral deficiencies.
With the growing obesity epidemic in the United States and a correlated rise in obesity-related conditions, such as diabetes, hyperlipidemia, and cardiovascular disease, physicians are struggling to find long-term solutions to help their patients adopt a healthier lifestyle and reduce the risk of chronic disease.
There are several barriers in counseling patients about nutrition, including shortage of time, patient noncompliance, inadequate teaching materials, lack of counseling training, lack of knowledge, inadequate reimbursement, and low physician confidence. However, the majority of physicians agree that dietary counseling is important and is the responsibility of physicians.1
Plant-based diets are an effective strategy to reduce or maintain a healthy weight and lower risk factors by lowering cholesterol, high blood pressure, and hemoglobin A1c levels. Furthermore, plant-based diets can lower the need for medications related to the aforementioned conditions, and therefore reduce the overall cost of healthcare. However, a plant-based diet is not a temporary plan but rather a long-term lifestyle change that requires commitment. Note: A recent Gallup poll stated that 5% of Americans define themselves as vegetarian and up to 10% call themselves vegetarian-inclined.2,3
There are 2 broad categories of plant-based diets: veganism and vegetarianism (Table 1). Veganism abstains from the use of all animal products, including dairy and eggs. Vegetarianism avoids consuming all meat, poultry, seafood, and flesh of animal.
Other variants of vegetarianism include:
• Lacto-ovo vegetarian: a vegetarian diet that eliminates animal flesh, but does include dairy and egg products
• Mediterranean: diet that consists of proportionally high consumption of olive oil, legumes, unrefined cereals, fruits, and vegetables, moderate to high consumption of fish, moderate consumption of dairy products (mostly cheese and yogurt), moderate wine consumption, and low consumption of meat and meat products
• Flexitarian: mostly vegetarian diet with occasional inclusion of meat products.
• Macrobiotic: staple of grains supplemented with local vegetables and avoiding highly processed or refined foods and most animal products.
• Raw food: diet that consists of eating only uncooked, unprocessed foods.
There is a growing trend in plant-based diets in the United States. Whether it’s for ethical, religious, nutritional, environmental, or even political reasons, vegetarianism is a daily part of life for many Americans.
Morbidity and Mortality
A 2013 cohort study of 96,469 men and women who participated in the Adventist Health Study 2 (AHS-2) found that vegetarian diets are associated with lower all-cause mortality (adjusted hazard ratio for all-cause mortality in combined vegetarians vs nonvegetarians was 0.88).4 These findings supported a 2012 meta-analysis by Huang et al which found a 9% lower all-cause mortality in over 124,000 vegetarians when compared to nonvegetarians.5 In a 1999 study of over 34,000 Seventh-day Adventist by Fraser et al,women lived 2.52 years and men 3.21 years longer than their meat-eating counterparts.6
There is a significant inverse association between fruit and vegetable consumption and mortality, with benefits apparent in ≥7 daily portions.7 When comparing equal amounts of fruit and vegetable consumption, vegetables are more nutritious. As such, countries like Australia have recently adopted the 5+2 campaign to encourage citizens to eat 5 servings of vegetables and 2 servings of fruit daily.
The impact of other comorbidities include:
•Diabetes. Multiple studies have demonstrated that vegetarian diets both decrease the risk of developing diabetes and improve insulin resistance. A 2011 analysis of data from 41,000 participants in AHS-2 found lower risk of developing diabetes among vegans (odds ratio [OR], 0.381), lacto-ovo vegetarians (OR, 0.618) and semi-vegetarians (OR, 0.486) as compared to nonvegetarians.8
A 2011 study by Kahleova et al compared a calorie-restricted vegetarian diet versus a conventional diabetic diet. The study concluded that calorie-restricted vegetarian diets had a greater capacity to improve insulin sensitivity, decrease diabetes medications (43% of participants vs 5% in control group), and body weight (a loss of 6.2 kg in participants vs a loss of 3.2 kg in the control group) when compared to a conventional diabetic diet.9
A 2006 randomized clinical trial compared glycemic control and cardiovascular risk factors in individuals with type 2 diabetes eating a low-fat vegan diet versus an American Diabetes Association (ADA) diet.10 While both groups demonstrated improvement, the low-fat vegan group had a 1.23 point lower hemoglobin A1c level versus a decrease of only 0.38 points in the ADA diet group.
A 2009 systematic review and meta-analysis demonstrated that red meat and processed meat were associated with an increased risk of diabetes.11
•Hypertension. There have been multiple studies demonstrating the beneficial effect of a vegetarian diet on reducing hypertension. In 2014, Yokoyama et al conducted a systemic review and meta-analysis of controlled clinical trials and observational studies.12 In the 7 controlled trials, vegetarians reported a 4.8 mm Hg reduction in systolic and 2.2 mm Hg lower diastolic blood pressure as compared to omnivores. In the 32 observational studies, vegetarians recorded a 6.9 mm Hg reduced systolic and 4.7 mm Hg lower diastolic blood pressure as compared to nonvegetarians.
Similarly, a 2005 literature review by Berkow et al found that in both observational and randomized studies, a vegetarian diet may be beneficial in reducing blood pressure.13 The blood pressure of vegetarians were lower by 3 mm Hg to 14 mm Hg (systolic) and 5 mm Hg to 6 mm Hg (diastolic). They also noticed that the prevalence of hypertension was lower, ranging from 2% to 40% in vegetarians and 8% to 60% in nonvegetarians.
A 2013 cross-sectional analysis of Seventh-day Adventists compared cardiovascular risk factors between vegetarian and nonvegetarian African Americans living in the United States.14 The results showed that the vegetarian group had a 44% lower risk of hypertension compared with nonvegetarians. This is significant because of the prevalence of hypertension in the African American population.
•Hyperlipidemia. In 2013, Fraser et al demonstrated that African American vegetarians had a 9.6 mg/dL low density lipoprotein-cholesterol (LDL-C) and 10 mg/dL lower triglycerides when compared to nonvegetarians.14 These findings were confirmed in 2 studies by Barnard et al. In 2000, they showed a13% decrease in total cholesterol and 17% decrease in LDL-C in postmenopausal women who followed a vegetarian diet for 2 months.15 In 2006, they compared a low-fat vegan diet to a traditional diabetic diet in patients with diabetes; the 22-week study resulted in a 21% decrease in LDL in the low-fat vegan diet compared to 10.7% decrease in the traditional group.16
•Cardiovascular disease. A 2012 meta-analysis by Huang et al found that mortality from circulatory diseases is 16% lower in vegetarians than in nonvegetarians.5 This supports a 1999 collaborative re-analysis of 5 prospective studies from Key et al that demonstrated a 24% reduction in ischemic heart disease in vegetarian versus nonvegetarian diets.17
•Cancer. Huang et al meta-analysis also found the overall cancer incidence is 18% lower in vegetarians than in nonvegetarians.5 In the 1999 analysis, Fraser et al identified that vegetarians reported lower risks for prostate and colorectal cancers as compared to nonvegetarians, but no significant difference in the risk for lung, breast, uterine, or stomach cancers.6
Consuming a strictly plant-based diet may result in some diet deficiencies, particularly due to the lack of essential nutrients that may be otherwise found in animal, fish, egg, and dairy products—in particular, B12,18 protein, essential amino acid lysine, N-3 fatty acids, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA),19 zinc, iodine, calcium, vitamin D, and iron.20 However, these potential deficiencies can be avoided with well-planned plant-based meals and fortified foods.
•B12. This is a water-soluble vitamin found in meat and other animal products.18 It is needed to produce red blood cells, synthesize nucleic acids, and maintain myelin sheaths.18 B12 deficiency may cause macrocytic anemia and peripheral nerve involvement, which may be irreversible in some cases. Furthermore, neurologic involvement may occur in the absence of anemia. Persons with B12 deficiency may also experience fatigue, cognitive dysfunction, and depression. Since B12 does not naturally exist in plant products, concern for the deficiency is highest in strict vegans.18 To avoid this deficiency, vegans and other plant-based diet followers can consume B12 fortified foods (eg, soy and cereals) or daily vitamin supplementation. Note: Lacto-ovo vegetarians can obtain adequate B12 from dairy products and eggs.
• Protein. Individuals consuming a strict plant-based diet may also be deficient in protein. Meats, dairy products, fish, and eggs are fairly high in well-digested proteins. People who exclude these from their diet may require higher protein intake than the recommended daily allowance since plant-based proteins are not as well-digested as other sources.19
Plant-based proteins may be obtained through soy protein, legumes, and some cereals. Lysine, an essential amino acid, may be lower in cereals and higher in soy, beans, brown rice, and quinoa.
Protein deficiencies can lead to edema, dermatitis, and thinning or discolored hair. These deficiencies are more often seen in developing countries where the plant-based diet is not as well rounded and based mostly on starch and sugars.
• N-3 fatty acids. EPA and DHA may be low in strict plant-based diets. These fatty acids are important for cardiovascular and eye health as well as brain development.19 Such deficiency may be avoided by incorporating soy milk and DHA-fortified foods derived from microalgae into the diet.
• Zinc. The zinc intake varies widely in persons on plant-based diets. Severe zinc deficiency can lead to a poor appetite, poor growth, hypogonadism, decline in wound-healing, and decreased cell-mediated immunity. Zinc may be found in soy products, legumes, grains, and nuts. Soaking grains and seeds in water reduces the phytic acid binding of zinc and increases its bioavailability.19
• Iodine. Plant-based diets may be low in iodine; sea salt and kosher salts are typically not iodized, therefore consider switching to an iodized version.
• Calcium. Plant-based diets may typically have lower calcium intakes than those that include dairy and eggs. Poor calcium intake can lead to hypocalcaemia, which may be asymptomatic or result in osteoporosis with increased risk of bone fracture, encephalopathy, paresthesias, muscle weakness, and in severe cases, tetany. Calcium intake can be increased by including low oxalate greens (eg, broccoli and kale) in the diet. Although sesame seeds, almonds, and dried beans are fairly high calcium sources, the bioavailability is not as high as cow’s milk. The best solution is supplement bioavailable intake with calcium-fortified foods.
• Iron. Both the source of iron and other foods consumed alongside iron can affect absorption and bioavailability. Plant-based iron is nonheme iron (opposed to heme iron in meats) and its absorption can be decreased by phytates, calcium, and the polyphenolics found in tea, coffee, and cocoa. Vitamin C and organic acids can enhance iron absorption.19
Note: Deficiencies in iron can lead to restless leg syndrome, pica, and brittle nails. Iron deficiency anemia is also a possibility but the prevalence is comparable to nonvegetarians.
Vegans do have lower iron stores.19 Plant-based iron rich foods include black beans, soybeans, spinach, raisins, cashews, and oatmeal.20
Clinicians and patients should have a clear understanding of the differences between a vegan and a vegetarian diet, as well as knowledge of the different subtypes of vegetarianism. When discussing plant-based diets with patients, clinicians should discuss the benefits and also the potential risks of associated nutrient deficiencies.
Since there are some clinical risks and benefits to take into account with either vegan or vegetarian diets,21 practitioners should discuss the reasons for their patient’s diet preferences—weight loss, lack of availability, budget and financial pressures, or religious, spiritual, and ethical beliefs.21
Proper advice on nutrient supplements, fortified foods, and other strategies to prevent malnutrition or deficiencies are essential for a healthy, plant-based lifestyle.
The clinician should ask the individual as to what foods will be excluded from their diet to help in balanced meal-planning and instruct on dietary supplementation. Remember, patients need to be motivated to adhere to the plant-based diet and the clinician’s role is to point out that this will require planning, label-reading, and discipline.22
Referring patients to a nutritionist is an important strategy to help patients build a diet plan that meets their needs and their tastes. A plant-based diet usually includes nutritional benefits, but should be balanced with the potential deficiencies and supplementations that are required to maintain good health (Table 2).
There is a growing body of evidence supporting the role of plant-based diets in reducing the risk of chronic diseases. As primary care practitioners, it is important that we encourage all patients, whether they are vegetarian or non-vegetarian, to increase their fruit and vegetable intake and limit the consumption of high-fat meats.
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2.Newport F. In U.S., 5% consider themselves vegetarians. Gallup. July 26, 2012. www.gallup.com/poll/156215/consider-themselves-vegetarians.aspx. Accessed August 2014.
3.Vegetarianism in America. Vegetarian Times. www.vegetariantimes.com/article/vegetarianism-in-america/. Accessed August 1, 2014.
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6.Fraser GE. Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-hispanic white California Seventh-day Adventists. Am J Clin Nutr.1999;70(3 Suppl):532S-538S.
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9.Kahleova H, Matoulek M, Malinska H, et al. Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with type 2 diabetes. Diabet Med. 2011;28(5):549-559.
10.Barnard ND, Cohen J, Jenkins DJ, et al. A low-fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes. Diabetes Care. 2006;29(8):1777-1783.
11.Aune D, Ursin G, Veierod MB. Meat consumption and the risk of type 2 diabetes: A systematic review and meta-analysis of cohort studies. Diabetologia. 2009;52(11):2277-2287.
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17.Pawlak R, Lester SE, Babatunde T. The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr. 2014;68(5):541-548.
18.Craig WJ, Mangels AR, American Dietetic Association. Position of the American dietetic association: vegetarian diets. J Am Diet Assoc. 2009;109(7):1266-1282.
19.Waldmann A, Koschizke JW, Leitzmann C, Hahn A. Dietary iron intake and iron status of German female vegans: results of the German vegan study. Ann Nutr Metab. 2004;48(2):103-108.
20.Plotnikoff GA. Nutritional assessment in vegetarians and vegans: questions clinicians should ask. Minn Med. 2012;95(12):36-38.
21.Tuso PJ, Ismail MH, Ha BP, Bartolotto C. Nutritional update for physicians: plant-based diets. Perm J. 2013;17(2):61-66.
22.Iverson K. When the patient asks: is a vegetarian diet healthy? J Am Acad Phys Asst. 2007;20(9):49.
Christopher Scuderi, DO, is the medical director of UF Health Family Medicine and Pediatrics in New Berlin, FL and an assistant professor in the department of community health and family medicine at the University of Florida in Jacksonville, FL.
Nipa R. Shah, MD, a family medicine physician, is the current chair of the department of community health and family medicine at the University of Florida, College of Medicine in Jacksonville, FL.
Charles Haddad, MD, is the medical director of the Dunn Avenue Family Practice and associate professor in the department of community health and family medicine, both at the University of Florida in Jacksonville, FL.
Judella Haddad-Lacle, MD, is the medical director of the Community Health and Family Medicine Clinic and an associate professor, both at the University of Florida in Jacksonville, FL.
Lori A. Bilello, PhD, is a research assistant professor in the department of medicine and the associate director for the Center for Health Equity and Quality Research at the University of Florida in Jacksonville, FL.
Gretchen Kuntz, MSW, MSLIS, is the director and clinical librarian at the Borland Health Sciences Library at the University of Florida in Jacksonville, FL.