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Vegetarian Diet
Summary and Conclusion: Vegetarian diet
Vegetarian diet and cancer:
T J Key et al found that cancer among meat eaters was 3.8%, among fish-eaters, 0.5%, and among vegetarians, 1.3%. The authors also found that compared to meat-eaters, vegetarians had a 53%, 45% and 74% reduced risk in bladder, leukemia, lymphoma, and stomach cancers, respectively. Looking at all cancers combined, vegetarians were 12 per cent less likely to develop cancer than meat eaters, while fish eaters were 18 percent less likely to develop cancer. (1)
The risk of colon cancer was higher in individuals with a high meat consumption, a low legume consumption, and a high body mass index (2).
High consumption of red meat was associated with an increased cancer risk of the oral cavity and pharynx (odds ratio [OR]= 3.65), esophagus (OR= 3.36), larynx (OR=2.91), stomach (OR= 2.19), colorectum (OR= 3.83), lung (OR= 2.17), breast (OR= 1.97), prostate (OR= 1.87), bladder (OR= 2.11) and kidney (OR= 2.72). Lamb was also associated with increased cancer risk. Eating a lot of processed meat was also linked to an increased risk of cancers of the esophagus (OR= 1.63), larynx (OR= 1.84), stomach (OR= 1.62), colorectum (OR= 2.15), lung (OR= 1.70) and breast (OR= 1.53). (3)
Men with the highest intake of allium vegetables (>10 g day of garlic, scallions, onions, chives, and leeks) had a 49% risk reduction of prostate cancer than did those in the category of lowest intake (4).
Eating fruits and vegetables, as well as vitamins A, C, and carotenoids from food was linked with a reduced risk of kidney cancer in men (6).
Vegetarian diet and mortality:
Campbell emphasized that a high consumption of animal-based foods were more likely to have had higher death rates and those with plant based diets had less. Also as a result of Campbell’s research with casein milk protein showed that cancer risk was increased as casein intake was increased. Therefore, avoid excessive milk protein intake until more research is completed. (5)
A meta-analysis found that all-cause mortality, mortality from circulatory diseases, and mortality from cerebrovascular diseases in vegetarians was lower than non-vegetarians by 9%, 16%, and 12%, respectively. Researchers also found a statistically reduced rate for vegetarians in ischemic heart disease mortality (29%) and cancer incidence (18%). (30)
Vegetarian diet and gastrointestinal health
Vegetarians with a reported average fiber intake of 41.5 g/day had a diverticular disease rate of 12%. In contrast, non-vegetarians had an average fiber intake of 21.4 g/day had a diverticular disease rate of 33%. (7)
For patients with Crohn’s disease, a semi-vegetarian diet with daily portions of brown rice, miso soup, brown rice, plain yogurt, eggs, vegetables, fruits, legumes, potatoes, algae and other plant foods with fish once per week and meat once every two weeks, resulted in remission from symptoms of Crohn’s disease in about 94% of patients over 2 years (8).
Vegetarian diet and weight loss:
A group which ate a low-fat vegan diet for 22 weeks lost on average 5.1 kg vs a gain of 0.1 kg in the control group and an average of 4.7 cm from their waist vs gain of 0.8 cm in the control group. Among the intervention group, 48.5% had a weight loss of 5% body weight compared to only 11.1% among the control group. (9)
Regular consumers of various types of beans had lower body weights, lower rates of obesity, and a smaller waist size (10).
Vegetarian diet and diabetes mellitus type 2:
Vegetarian diets are associated with reduction in diabetes incidence compared to non-vegetarians (11).
Vegetarian diet, weight loss, and cholesterol:
A vegetarian diet over a period of 74 weeks reduced bodyweight (-4kg), HbA1C (-0.34), total cholesterol (-20.4 mg/dL ), and LDL(-13.5 mg/dL) which was slightly better than a conventional American Diabetic Association diet (12).
The intake of flavonoids from mainly vegetables (72.3%), fruits (15.6%), green tea (5.4%), potatoes (3.8%) and pulses (tofu) (2.9%) was found to be inversely related to LDL levels (33).
Vegetarian diet and hypertension: Following a diet rich in fruits, vegetables, and low fat dairy products, bp in subjects without hypertension improved from an average bp of 131.3/84.7 at baseline to an average of 125.8/81.7, and in those with hypertension (bp over 140/90), systolic and diastolic bp improved by 11.4 and 5.5 points respectively over the control diet (13).
Vegetarians and nutritional concerns:
Vegetarians and vegans have a higher risk of iodine deficiency and should ensure that they are obtaining the recommended iodine intake (14). Iodine recommendations according to age may be found at: Nutritive Value of Foods, United States Department of Agriculture, Agricultural Research Service, Home and Garden Bulletin Number 72. May be accessed at: http://www.nal.usda.gov/fnic/foodcomp/Data/HG72/hg72_2002.pdf and http://www.ars.usda.gov/Services/docs.htm?docid=22769 (38).
The Food and Nutrition Board Institute of Medicine expressed that vegetarians should double the following recommended daily allowance of iron since the non-heme iron found in plant foods is not as well absorbed as heme-iron found in meats: infants 0-6 months, 0.27 mg; 7-12 month olds, 11 mg; children 1-3 years old, 7 mg; 4-8 year olds, 10 mg; 9-13 year olds, 8 mg; males 14-18 years old, 11 mg; females 14-18 years old, 15 mg; all males over 18 years old, 8 mg, females age 19-50, 18 mg; females over age 50, 8 mg; all pregnant women, 27 mg; lactating females under age 18, 10mg; and lactating females over age 18, 10 mg (16). Hunt, JR mentioned that the exception may be in vegetarian men, who were able to obtain enough iron from diet alone (17). This author also expressed the importance in being screened for excess iron stores by your physician before starting iron supplements as well as to attempt using iron-rich vegetarian foods instead of iron supplements due to the unknown risk of using iron supplements long term (17). Daily allowance of iron may be found at the following link for all ages:
Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press, 2001. http://iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Elements.pdf (19)
Hunt JR suggested that vegetarians may require 50% more zinc than non-vegetarians (18), and the Food and Nutrition Board Institute of Medicine recommended to double the following amount of zinc intake due to reduced absorption from a higher amount of phytate contained in plant tissues (19): infants 0-6 months, 2 mg; 7-12 month olds, 3 mg; children 1-3 years old, 3 mg; 4-8 year olds, 5 mg; 9-13 year olds, 8 mg; all males over 14 years old, 11 mg; females 9-13 years old, 8 mg; females age 14-18, 9 mg; females over age 18, 8 mg; all pregnant women under 18 years old, 12 mg, all pregnant women age 19-50, 11 mg; lactating females under age 18, 13mg; and lactating females over age 18, 12 mg. Daily allowance of zinc may be found at the following link for all ages: Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press, 2001. http://iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Elements.pdf (19)
Vegetarian diet and beta-carotene:
A blood beta-carotene concentration less than 0.28 micromol/L has been linked with a higher risk of several cancers, while a concentration of more than 0.28 to 0.37 micromol/L have been associated with a reduced risk of several cancers in prospective blood concentration studies. Eating a variety of 5 fruits and vegetables per day provides the individual with about 5.2 to 6 mg/day of food based beta-carotene. This allows plasma carotenoid levels to rise above a range represented in studies which were associated with a lower risk of cancer and all-cause mortality compared to those with a lower food based carotenoid levels. (22)
The U.S. Preventive Services Task Force (USPSTF) recommends against the use of beta-carotene supplements, alone or in combination (40). Intake of vegetables containing beta carotene was associated with a lower risk for all causes of death including cancer but no benefit was seen with taking beta-carotene supplements (42). An increased risk of mortality was associated with use of beta-carotene and vitamin E supplements (43).
.Vegetarian diet and B12 deficiency:
In vegetarian women, supplementation of vitamin B12 is required due to the lack of this vitamin in vegetarian foods. (20)
In a study involving 816 subjects (368 with coronary artery disease [CAD] and 448 controls) in India, levels of vitamin B12 were found to be significantly lower in patients with CAD, as compared to controls. In this study interestingly, vegetarians who were found to have lower levels of vitamin B12 were noted to have a higher incidence of coronary artery disease compared to non-vegetarians. (21)
Vegetarian diet and vitamin C: A cohort study in the U.K. by Khaw KT et al found that people with the highest ascorbic acid levels (vitamin C levels) had half the risk of dying from all causes, and a 20 micromol/L increase in blood ascorbic acid level was equivalent to a 50 g per day increase in fruit and vegetable intake, was associated with about a 20% reduction in risk of all-cause mortality. (29)
Vegetarian diet and heart disease:
A vegetarian diet group compared to a control diet starting 24-48 hours after an acute myocardial infarction (acute MI) showed a 34.5% decrease in total cardiac disease events which included fatal acute MI, non-fatal acute MI, and sudden cardiac death. (44)
A study in Denmark revealed that the maximum benefit of eating fruits and vegetables toward reduction of ischemic heart disease was reached at a maximum intake of 800 grams of fruits and vegetables per day (31).
Vegetarian diet and skin health: Decreased skin wrinkling around the corners of the eyes was observed in women with higher intakes of green and yellow vegetables (32).
Vegetarian diet and mood: Among subjects on a low calorie diet, mood was significantly better in a vegetarian group verses a mixed diet group (34).
Vegetarian diet and AAA: Kent et al found that consumption of nuts, vegetables, and fruits were associated with a reduced risk of abdominal aortic aneurysm (35).
Vegetarian diet and rheumatoid arthritis: In patients with rheumatoid arthritis, subjects which fasted for 7-10 days, followed by an individually adjusted gluten-free vegan diet for 3.5 months, followed by a 9-month lactovegetarian diet showed improvement in all clinical variables, and positively influenced measures of inflammation and disease activity even after a year of follow up (36).
A vegetarian diet may reduce the number of hospitalizations, surgeries, rates of allergic disease, and use of medications (37).
