By Lauren Boyd, Desiree Udarbe & Sarah Peterson

The Effect of a Vegan/Vegetarian Diet on Diabetes and Insulin Resistance By Lauren Boyd, Desiree Udarbe & Sarah Peterson

The Effect of a Vegan/Vegetarian Diet on Diabetes and Insulin Resistance • Approximately 90 to 95% of all diagnosed cases of diabetes are type 2 diabetes mellitus (T2DM) • Prevalence of T2DM increases with age and is being diagnosed increasingly in children and adolescents • factors that increase the risk of developing T2DM • Obesity • family history/history of gestational diabetes mellitus • impaired glucose metabolism • physical inactivity

How T2DM different from Type 1 Diabetes Mellitus? • Type 1 diabetes mellitus develops from a lack of insulin due to the destruction of beta cells in the pancreas • T2DM results when individuals are producing insulin but their tissues are resistant to the insulin. • This type of insulin resistance causes the pancreas to increase production of insulin. Over time, the pancreas loses its ability to produce insulin and consequently, causes metabolic defects in the individual. • Insulin resistance and relative insulin deficiency are two common defects observed in individuals with T2DM.

Causes Of Insulin Resistance in T2DM • Insulin resistance is caused by a cell-receptor defect. • This defective insulin secretary response results in a surplus of glucose production from the liver since insulin is responsible for inhibiting gluconeogenesis and glycogenesis when blood glucose is high. • In T2DM • First, postprandial glucose levels increase • Then, hepatic gluconeogenesis responds to the lack of glucose and the response causes fasting hyperglycemia.

Conventional Treatment For T2DM • T2DM is conventionally treated by observing three factors that play a role is glycemic control: • Hepatic glucose production • Glucose uptake by the periphery • Absorption of glucose from food • Medical therapy of T2DM emphasizes nutrition therapy, physical activity and use of medications to normalize glycemic control. • Use of medications for T2DM is only observed in individuals who cannot accomplish glycemic control through nutrition therapy and physical activity.

Conventional Treatment Goals For T2DM According to Nutrition Therapy Guidelines, to promote a lifestyle for the patient that will result in better metabolic control. Conventional nutrition intervention for T2DM involves: • moderate weight loss for individuals with BMIs>25 kg/m2 • monitoring total grams of carbohydrates • assuring protein intake does not exceed 20% • assuring fat intake is less than 25-35% of total kcal • less than 7% of fat from saturated fat • increasing fiber intake. According to studies, fiber decreases the rate of absorption of glucose from the small intestine, resulting in a positive effect on serum glucose levels Guidelines enforce monitoring total grams of carbohydrates because it is an accurate predictor of glycemic response and a strategy to help achieve improved glycemic control.

A Vegetarian Diet And T2DM • According to research, T2DM is only half as prevalent in vegetarians compared to non-vegetarians. • Evidence shows that a vegetarian diet improves carbohydrate and lipid abnormalities in diabetes. • Randomized controlled intervention studies in patients with T2DM have shown greater rates of weight loss, reduced fasting plasma glucose levels, improvements in Hb A1c values and reduced uses of diabetes medications compared with conventional diets used for the treatment of diabetes.

A Vegetarian Diet And T2DM Cont. Proposed mechanisms of interest that may help explain the beneficial effect of implementing a vegetarian diet in individuals with T2DM include: • higher intakes of fiber • lower intakes of saturated fat • an improved polyunsaturated and saturated fat ratio • higher intakes of non-heme iron • reduced iron stores • higher intakes of plant proteins and plant sterols • higher consumptions of antioxidants.

A Vegetarian Diet And T2DM • Studies have shown that increased fiber intake is associated with reductions in blood glucose, and fasting insulin in T2DM. Evidence shows that viscous fibers play a role in improving postprandial glycemia in both individuals with T2DM and individuals without T2DM. • According to a meta-analysis , selection of plant-based, low glycemic index foods was expected to allow increased consumption of carbohydrates in replacement of animal protein in the vegetarian diet, without altering the glycemic control in the postprandial period. • Evidence has revealed that there is an overall benefit in T2DM in correlation with consuming low glycemic index foods. • Therefore, the importance of slowing the rate of carbohydrate absorption is critical in improving metabolic control in patients with T2DM.

Study 1 “Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with Type 2 diabetes”Kahleova H, Matoulek M, Malinska H, et al. • The study evaluated insulin resistance and oxidative stress markers in patients with type 2 diabetes in correlation with a vegetarian diet and conventional diet. • 24 week randomized, open, parallel, metabolically controlled design • 74 subjects with type 2 diabetes • n=37 vegetarian diet • n=37 conventional diet

Study 1 Parameters • Patients randomly assigned to vegetarian diet group or the conventional diabetic diet group. • REE Measurements were recorded by indirect calorimetry to create a calorie restriction of 500 calories per day and isocaloric diets for all subjects. • All meals were provided during the study. • Weekly meetings were used to encourage compliance to the prescribed diets All measurements were recorded at baseline, 12 weeks, and 24 weeks on an outpatient basis, after 10-12 hour overnight fasting. • Height, weight, waist circumference • Insulin sensitivity • Volume of visceral and subcutaneous fat • Oxidative stress markers

Study 1 Diets The vegetarian diet: • Animal products were limited to one portion of low-fat yogurt per day. • Energy breakdown • ~ 60% from carbohydrates • 15% from protein • 25% from fat. The conventional diabetic diet: • Administered according to the dietary guidelines of the diabetic and nutrition study group of the European Association for the study of diabetes. • Energy breakdown: • 50% from carbohydrates • 20% from protein • less than 30% from fat. • Vitamin B12 was supplemented to both groups to maintain the same level of intervention.

Study 1 Results • Both groups reduced energy intake (P<0.001 for each group). • Carbohydrates percent increased in the experimental group (P=o.oo2) • No significant changes observed in the control group • Fat percent decreased in both groups (P=0.03) • Protein percent and cholesterol decreased in experimental group (P<0.001).

Study 1 Results A calorie restricted vegetarian diet these more than a conventional diabetic diet in patients with type 2 diabetes: • Increased insulin sensitivity • Reduced volume of visceral fat • Improved plasma concentration of oxidative stress markers Other mechanisms observed that may explain the beneficial effects of a vegetarian diet are: • higher intakes of fiber • lower intakes of saturated fats • higher intakes of non-heme iron • reductions of iron stores • higher intakes of plant proteins, antioxidants and plant sterols.

Study 1 Limitations • The number of subjects in the study did not provide enough power to confirm the effects of the vegetarian diet on Hb A1c values. • The subject’s level of adherence to the prescribed diets was somewhat poor in the conventional diabetic diet group and may have swayed the results of the study. • Non-isocaloric diets may add confounding factors

Study 1 Conclusion The authors conclude that a vegetarian diet may provide a beneficial, effective alternative nutrition therapy for type 2 diabetes. The study concludes that the advantages of a vegetarian diet in type 2 diabetes correlate with • weight loss, specifically visceral fat reduction • improvements in plasma concentrations of oxidative stress markers. These two factors may be responsible for the increased insulin sensitivity observed.

Study 1 Grade • Strong, parallel design that allowed the investigators to use weekly meetings in both groups to keep subject committed and motivated. • Providing all meals under supervision allowed the investigators to maintain a level of control and integrity among their subjects consumption. • The study length allowed for the subjects to adjust to each prescribed diet. • Results are void of any serious doubt about bias, or flaws in the research design with no observed inconsistencies within the data analyzed. • We gave this study a grade of A-

Study 2 “A Low-Fat Vegan Diet and a Conventional Diabetes Diet in the Treatment of Type 2 Diabetes: A Randomized, Controlled, 74-wk Clinical Trial” Barnard ND, Cohen J, Jenkins DJ et al. • The study compared the effects of a low-fat vegan diet on glycemia, weight and plasma lipids in individuals with type 2 diabetes. • 74 week randomized, control trial • 99 subjects with type 2 diabetes • n = 49 vegan diet • n = 50 conventional diet

Study 2 Parameters Parameters of trial: • Randomly assigned to diet • Dinner was provided for subjects during study • Weekly hr meeting with their group (Wks 1-22) • Biweekly hr meeting with their group (Wks 23-72) • Dietary records kept for 3 day periods (Wk 0, 11, 22,74) • 2 week days, 1 weekend day • Hb A1C, plasma glucose & plasma lipid tests (Wk 0, 11, 22, 35, 48, 61, 74)

Study 2 Diets Vegan Diet: • Composed of vegetables, fruit, grains & legumes • Energy breakdown • 75% carbohydrate • 15% protein • ~10% fat Conventional diet: • Based on the individual; followed 2003 ADA guidelines • Energy breakdown • 60-70% carbohydrate/monounsaturated fats • 15-20% protein • <7% saturated fat • *500-1000 kcal reduction was applied to those with BMIs>25

Study 2 Results * Weight loss was found to be significantly associated with Hg A1C changes. For each kg of weight lost, a decrease of 0.09 in Hg A1C.

Study 2 Limitations • Insufficient sample size • All meals were not provided for subjects adding confounding factors • Groups had non-isocaloricdiets; no calorie restrictions which would add confounding factors to the results

Study 2 Conclusion The authors concluded that a vegan diet may an effective alternative diet to those with type 2 diabetes • both diets improved controlling glycemia and plasma lipids, but the vegan diet was more effective • benefits of vegan diet on diabetes complication is not yet established

Study 2 Grade • Design was a randomized, controlled study • Study was 74 weeks long • Included 99 subjects • The questions asked had clear outcomes • We gave this study a grade A-

Study 3 “A Low-Fat Vegan Diet Improves Glycemic Control and Cardiovascular Risk Factors in a Randomized Clinical Trial in Individuals with Type 2 Diabetes.”Barnard ND, Cohen J, Jenkins DJA et al. • The study investigated whether a low-fat vegan diet improves glycemic control and cardiovascular risk factors in individuals with type 2 diabetes • 22 week randomized, controlled trial • 99 subjects with Type 2 Diabetes • n = 49 vegan diet • n = 50 conventional diet

Study 3 Parameters Parameters of trial: • randomly assigned to diet ( 49 vegan, 50 conventional) • weekly hr meeting with their group (Wks 1-22) • Dietary records kept for 3 day periods (two weekdays, 1 weekend,) (Wk 0, 11, 22,) • 24-Hour recalls (wk 4,8,13,20) • Hb A1C (0,11,22)

Study 3 Diets Vegan Diet: • composed of vegetables, fruits, grains & legumes • Foods to avoid: animal products, added oils, avocados, olives, nut, nut butters, seeds • vitamin B12 supplement • Energy breakdown • 75% carbohydrate • 15% protein • 10% fat Control diet: • followed 2003 ADA guidelines • Energy breakdown • 60-70% carbohydrate/monounsaturated fats • 15-20% protein • <7% saturated fat

Study 3 Results Results: *weight loss was associated a decrease in HbA1c; .12% decrease in Hb A1C/kg weight lost(Person correlation, r=0.51) (P<0.0001)

Study 3 Limitations • Insufficient sample size • No meals were provided leading to more confounding factors

Study 3 Conclusion The authors concludedthat: • both a low-fat vegan diet and a diet following ADA guidelines improved glycemic control • greater changes were found in the vegan group • no long term effects and sustainability established

Study 3 Grade • Randomized, controlled trial • 22 weeks long • 99 subject • No meals were provided • We gave this study a grade of A-

Conclusions The purpose was to determine if a vegetarian/vegan diet would improve insulin sensitivity, blood glucose and Hb A1c levels in individuals with Diabetes. All studies compared either vegetarian/vegan diets with a control diet. Vegetarian/vegan diets had greater improvements in • insulin sensitivity • Hg A1c • weight loss We concluded from this research that it may benefit individuals with Diabetes to follow a vegan or vegetarian diet. Following this diet is shown to result in greater improvements in insulin sensitivity, Hg A1c and blood glucose levels than the recommended Diabetes Guidelines.

Overall Level of Evidence We graded the level of evidence and the strength of our conclusion with a grade II. Although the results were consistent and clinically important and there study design was strong, we found important flaws in the dietary orders, such as non-isocaloric diets that could affect the results of the study. A larger sample size would be beneficial.

Public Health Recommendation We recommend a vegetarian or vegan diet as an alternative nutritional therapy in Type 2 Diabetes. The studies reviewed suggest that following this diet will improve blood sugar and lipid levels. Researchers have claimed that one of the major benefits may be weight loss. This may be due to higher levels of fullness. It is highly unlikely that following this diet would have negative effects. More research is needed to see the results of a long term vegetarian or vegan diet in patients with type 2 diabetes.

References 1. “Vegetarian Diet Improves Insulin Resistance and Oxidative Stress Markers More Than Conventional Diet in Subjects with Type 2 Diabetes” Kahleova, H., Matoulek, M., Malinska, H., Oliyarnik, O., Kazdova, L., Neskudla, T., Skoch, A., Hajek, M., Hill, M., Kahle, M. & Pelikanova, T. Diabetic Medicine: a Journal of the British Diabetic Association. 2011;28:549-559. 2.“A Low-Fat Vegan Diet Improves Glycemic Control and Cardiovascular Risk Factors in a Randomized Clinical Trial in Individuals with Type 2 Diabetes”. Barnard ND, Cohen J, Jenkins DJA, Turner-McGrievy G, Gloede L, Brent J, Seidl K, Green AA, Talpers S. Diabetes Care. 2006; 29. 8. 1777-1783. 3.“A Low-Fat Vegan Diet and a Conventional Diabetes Diet in the Treatment of Type 2 Diabetes: A Randomized, Controlled, 74-wk Clinical Trial” Barnard ND, Cohen J, Jenkins DJ, Turner-McGrievy G, Gloede L, Green A, Ferdowsian H. American Journal of Clinical Nutrition. 2009; 89. 1588S-1596S. 4. 1. Jenkins DJA, Kendall CWC, Marchie A, et al. Type 2 diabetes and the vegetarian diet. Am J ClinNutr. 2003;78:610S. 5. VangA, Singh PN, Lee JW, Haddad EH, Brinegar CH. Meats,processedmeats, obesity, weight gain and occurrence of diabetes among adults: findings from Adventist Health Studies. Ann NutrMetab. 2008;52:96–104. 6. Snowdon DA, Phillips RL. Does a vegetarian diet reduce the occurrence of diabetes? Am J Public Health. 1985;75:507– 512.9. Fraser G.

By Lauren Boyd, Desiree Udarbe & Sarah Peterson