Vegetarian Diets in the Prevention and Management of Diabetes and Its Complications Roman Pawlak
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Vegetarian Diets in the Prevention and Management of Diabetes and Its Complications Roman Pawlak ■ IN BRIEF Epidemiological studies have found a lower prevalence of type 2 diabetes among vegetarians compared to nonvegetarians. This reduced risk is likely a function of improved weight status, higher intake of dietary fiber, and the absence of animal protein and heme iron in the diet. Interventional studies have shown that vegetarian diets, especially a vegan diet, are effective tools in glycemic control and that these diets control plasma glucose to a greater level than do control diets, including diets traditionally recommended for patients with diabetes (e.g., diets based on carbohydrate counting). Vegetarian diets are associated with improvement in secondary outcomes such as weight reduction, serum lipid profile, and blood pressure. Studies indicate that vegetarian diets can be universally used in type 2 diabetes prevention and as tools to improve blood glucose management. iet plays an important role diets exclude all meats and animal in diabetes prevention and products. Dmanagement. According to There are additional variations the American Diabetes Association within each of the above categories. (ADA), a variety of eating patterns For example, some individuals who are acceptable for the management consider themselves vegans do not eat of diabetes (1). The impacts of veg- honey or other bee products, whereas etarian eating patterns on the risk of others just limit their dietary exclu- type 2 diabetes, glycemic control, and sions to dairy products and eggs. In prevention of diabetes comorbidities addition, plant-based diets are an have been the focus of several recent eating pattern that mainly includes research studies. unrefined foods of plant origin but Vegetarian diets encompass several may include small amounts of meats, diet types, including semi-vegetarian mainly white meat. (flexitarian), pesco-vegetarian, Vegetarian diets have been asso- lacto-vegetarian, ovo-vegetarian, ciated with improvements in many lacto-ovo-vegetarian, vegan, and raw- modifiable heart disease risk factors, food vegan diets. Semi-vegetarians including serum lipid profile, serum East Carolina University–Nutrition Science, include small amounts of meat, glucose concentration, and systolic Greenville, NC mainly from fish and poultry. and diastolic blood pressure (2–5). Corresponding author: Roman Pawlak, Pesco-vegetarians ingest some fish, Consequently, vegetarians have been [email protected] in addition to foods of animal and shown to have a lower risk of hospital- https://doi.org/10.2337/ds16-0057 plant origin. Milk and dairy prod- ization or death from ischemic heart ucts are ingested by lacto-vegetarians; disease (6). Furthermore, vegetarian ©2017 by the American Diabetes Association. Readers may use this article as long as the work ovo-vegetarians include eggs; and lacto- diets have been shown to regress is properly cited, the use is educational and not ovo-vegetarians ingest both dairy arterial stenosis among heart dis- for profit, and the work is not altered. See http:// creativecommons.org/licenses/by-nc-nd/3.0 products, including milk, and eggs. ease patients (7). These diets are also for details. Individuals who adhere to vegan associated with reduced risk of other 82 SPECTRUM.DIABETESJOURNALS.ORG PAWLAK health conditions, including type 2 women (OR 0.25 [95% CI 0.15– Diabetes Association. The trial lasted diabetes, some types of cancer, diver- 0.42] for diabetes and OR 0.73 [95% for 12 weeks. Although A1C signifi- ticular disease, and cataracts (8–11). CI 0.56–0.95] for IFG). The odds for cantly decreased in both groups, the This manuscript is a review of the premenopausal women were not sta- improvement was greater among par- impact of vegetarian diets on diabe- tistically significant for either diabetes ticipants in the vegan group (–0.5%, tes. The specific objectives included: (OR 0.26 [95% CI 0.06–1.21]) or P <0.01 vs. –0.2%, P <0.05). This 1) assessment of the incidence of type IFG (OR 0.60 [95% CI 0.35–1.04]). difference became greater when the 2 diabetes among vegetarians in com- Vegetarians living in North analysis was restricted to patients parison to nonvegetarians, 2) review America also have lower odds of with the highest rate of compliance of the impact vegetarian diets have on being diagnosed with type 2 dia- to the respective diets (–0.9% in the type 2 diabetes management/blood betes, according to results from the vegan group and –0.3% in the con- glucose control and treatment, and 3) Adventist Health Study 2 (8), which ventional group, P = 0.010). evaluation of the influence of vegetar- included 15,200 men and 26,187 The beneficial effects of vegetar- ian diets on diabetes comorbidities. women. Compared to nonvege- ian diets described above indicate PRACTICE FROM RESEARCH TO Vegetarian Diets and Incidence tarians, vegans had the lowest risk that these diets might be effective in of Type 2 Diabetes (OR 0.381 [95% CI 0.236–0.617]), diabetes management and treatment. followed by semi-vegetarians (OR The effect of vegetarian diets on This conclusion is supported by find- 0.486 [95% CI 0.312–0.755]) and the risk of developing type 2 diabe- ings reported by Barnard et al. (16), in lacto-ovo-vegetarians (OR 0.618 tes has been assessed in a few large a study with 99 individuals with type [95% CI 0.503–0.760]). This trend studies with individuals of different 2 diabetes. Participants were divided was similar among both black and sexes, ethnic backgrounds, and geo- into group 1, with 49 people between nonblack participants. graphical locations. In a recent study, 33 and 82 years of age who were Agrawal et al. (12) reported an asso- Vegetarian Diets in Type 2 assigned to a vegan diet, and group ciation between the consumption of Diabetes Management and 2, with 50 people between 27 to 80 a vegetarian diet and the occurrence Blood Glucose Control and years of age who were assigned to fol- of type 2 diabetes in a nationally rep- Treatment low a diet recommended by the ADA resentative sample of 156,317 East Results of a meta-analysis (14) that based on carbohydrate counting. The Indian participants who were 20–49 assessed the impact of vegetarian di- first group was advised to consume years of age. Individuals who adhered ets on plasma glucose suggested that vegetables, fruits, whole-grain cereals, to any type of vegetarian diet except such diets are effective in blood glu- and beans. The amounts of calories for vegan had statistically significant cose management. The analyses were and carbohydrates consumed were lower odds of diabetes (odds ratio based on six interventional studies not limited. Carbohydrates consti- [OR] 0.67 [95% CI 0.58–0.76], involving 255 individuals. Five of tuted ~75% of consumed calories, P <0.01 for lacto-vegetarians; OR the studies assessed the effect of a with the remainder provided by fat 0.70 [95% CI 0.51–0.96], P = 0.03 vegan diet, whereas the sixth assessed (10%) and protein (15%). for lacto-ovo-vegetarians; and OR a lacto-ovo-vegetarian diet. The study Participants in both groups 0.77 [95% CI 0.60–0.98], P = 0.03 periods varied from 4 to 74 weeks reduced their caloric intake from for semi-vegetarians). The association (average 23.7 weeks). Adhering to a 1,759 ± 468 to 1,425 ± 427 kcal/day for vegans was not statistically signifi- vegan or vegetarian diet resulted in (P <0.0001) in the vegan group and cant (OR 0.91 [95% CI 0.61–1.36], a statistically significant lower mean from 1,846 ± 597 to 1,391 ± 382 P = 0.643). A1C (–0.39 percentage points [95% kcal/day (P <0.0001) in the control The results described by Agrawal CI –0.62 to –0.15], P = 0.001) com- group. Protein intake among vegans et al. are consistent with findings pared to A1C among participants dropped from 77 ± 27 to 51 ± 16 g/day from another Asian study from from control diets. No heterogeneity (P <0.0001), whereas in the control Taiwan (13). This study included was observed among study results group it decreased from 85 ± 27 to 4,384 individuals who were Buddhist (P = 0.389 for heterogeneity). 73 ± 23 g/day (P <0.002). Similarly, volunteers. The reported analyses Since the meta-analysis described fat intake fell in both groups from 72 were sex and age specific. Vegetarian above was published, Lee et al. (15) ± 28 to 30 ± 19 g/day (P <0.0001) in men had statistically significant lower published results of a study in which the experimental group and from 73 odds for both diabetes (OR 0.49 they assessed the impact of a brown ± 35 to 52 ± 21 g/day (P <0.0001) in [95% CI 0.28–0.89]) and impaired rice–based vegan diet on glycemic the control group. Conversely, carbo- fasting glucose (IFG; OR 0.66 [95% control among 46 Korean patients hydrate intake increased from 205 ± CI 0.46–0.95]). A similar pattern and 47 control participants who used 69 to 251 ± 70 g/day (P <0.0001) in was observed for postmenopausal a diet recommended by the Korean the vegan group and from 213 ± 70 VOLUME 30, NUMBER 2, SPRING 2017 83 FROM RESEARCH TO PRACTICE / PERSPECTIVES ON MEAL PLANNING to 165 ± 51 g/day (P <0.0001) in the control group. Before switching to a vegan diet After switching to a vegan diet After 22 weeks, individuals as- signed to consume the high-carbo- hydrate vegan diet lowered their A1C from an average of 8.0 to 7.1% Average monthly decrease in creatinine (12.6%).