Vegetarianism and Women’s Health
June 2000; Volume 2; 41-44
By Neal D. Barnard, MD
From dysmenorrhea to cancer, sex hormones have key roles in many disorders. Research over the past two decades has shown that the concentration and activity of sex hormones, particularly estrogens, are strongly modified by low-fat and vegetarian diets, leading to the possible use of dietary changes in medical interventions.
Diet and Estrogen
Vegetarians typically have lower serum estrogen concentrations compared to omnivores, apparently because of differences in both fat and fiber intake.1-6 Dietary fat influences plasma fatty acid concentrations which, in turn, correlate with serum levels of bioavailable estrogens.7 Cutting fat intake reduces serum estrogen levels in both pre- and postmenopausal women, an effect demonstrated for total estrogens, estradiol, estrone, and estrone sulfate.7-11
Vegetarians also have increased fecal estrogen excretion, apparently caused by the ability of dietary fiber to reduce enterohepatic circulation.5 In a group of vegetarian women, daily fiber intake averaged 25-33 g, compared to 11-13 g for omnivores, and fiber intake correlated with fecal estrogens.12 Clinically significant effects may also be seen with much smaller differences in fiber intake. Dutch researchers studied the eating habits of a group of young girls and found that those who ate the most vegetables ingested about 20 g/d of fiber, about 2 g/d more than girls who ate the least vegetables. Those eating the most vegetables also had lower serum estrogen levels and reached puberty slightly later.13 The deconjugation of estrogens in the intestine, which encourages their reabsorption, also appears to be reduced by low-fat and high-fiber diets.9,12
Diet also influences hormone activity. High-fiber, plant-based diets increase serum concentrations of sex-hormone binding globulin (SHBG), increasing estrogen binding and reducing hormone bioavailability.5,14 A recent study using a low-fat, vegan (pure vegetarian) diet in premenopausal women showed a 19% increase in serum SHBG concentration after approximately five weeks (P < 0.001).15 Although this increase was independent of body weight, SHBG binding capacity is also inversely correlated with body weight, which is lower in vegetarians.16 In vitro studies have shown that nonesterified fatty acids (NEFAs) reduce the binding of estradiol to SHBG. Saturated short-chain (8-12 carbon) NEFAs and polyunsaturated NEFAs caused more inhibition of binding than did the longer chain saturated or monounsaturated NEFAs.17
Vegetarian diets are not only generally low in fat and high in fiber, they are also often rich in soy products, beans, and other foods high in phytoestrogens, which displace estrogens from estrogen receptors.5 Soy protein also appears to affect the pituitary-ovarian axis. The addition of 60 g/d of soy protein to the diets of premenopausal, nonvegetarian women was associated with a lengthening of the follicular phase by a mean of 2.5 days and lower midcycle peaks of luteinizing hormone and follicle stimulating hormone.18
Dysmenorrhea and Other Conditions
Approximately one in 10 women in their early reproductive years suffers from severe dysmenorrhea (usually primary).19 Its cause is believed to be related to uterine muscle contraction and ischemia induced by prostaglandins (particularly PGE2 and PGF2a) produced in endometrial tissue under the influence of estrogens and progesterone.20,21 Premenstrual symptoms affect an estimated 20-40% of women, with up to 5% experiencing significant adverse effects on work or social adjustment.22 A recent study compared the effect of a low-fat, vegan diet to placebo on dysmenorrhea and premenstrual symptoms.15 Mean dysmenorrhea duration fell significantly from 3.9 ± 1.7 days at baseline to 2.7 ± 1.9 days after two menstrual cycles (P < 0.01). Pain intensity also fell significantly, as did mean durations of premenstrual symptoms related to poor concentration, restriction of social activities, and water retention. In an earlier study of 30 healthy women, a reduction in dietary fat from 40% to 20% of energy was associated with reduced premenopausal water retention.23
A possible mechanism for the effect of a vegetarian diet is that elevated serum SHBG and/or reduced serum estrogen concentrations reduce estrogenic stimulation of the endometrium, limiting the proliferation of tissues capable of producing prostaglandins. In addition, while green leafy vegetables and beans are typically low in total fat, the ratio of omega-3 fatty acids to other fats is often high.24 Omega-3 fatty acids are precursors of 3-series prostaglandins, which have anti-inflammatory actions. In contrast, diets rich in animal fats and cooking oils are proportionately richer in omega-6 fatty acids, which promote the formation of PGE2 and PGF2a. In a group of Danish women, a higher intake of omega-3 fatty acids or a higher ratio of omega-3:omega-6 fatty acids was associated with reduced menstrual pain.25
One study suggests that vegetarians may have fewer anovulatory cycles. Twenty-three vegetarians and 22 nonvegetarians with no overt symptoms of menstrual abnormalities were evaluated; 15% of nonvegetarians’ cycles were anovulatory, compared to fewer than 5% of those of the vegetarians.6 While the hormonal effects cited above may have played a role, the vegetarians weighed less, as is typically the case, and were much less likely to have been on calorie-restricted diets for weight loss, suggesting the possibility that calorie-restricted diets among meat-eaters may have contributed to their menstrual disturbances.
Osteoporosis
Calcium balance requires planning on any diet, but is no more of a challenge with vegan diets than with other regimens. Green leafy vegetables and legumes are significant calcium sources, and fortified juices and soy milks are especially calcium-rich. Also, calcium losses are increased by animal proteins, which are avoided on vegan diets. Calcium losses are also aggravated by dietary sodium, excessive caffeine intake, tobacco use, and sedentary lifestyle. Milk drinking offers no apparent advantage from the standpoint of bone integrity. In the Harvard Nurses’ Health Study of 77,761 women aged 34-59, those who got the most calcium from dairy sources had slightly, but significantly, higher risk of hip fractures over a 12-year follow-up period, compared to those who drank little or no milk, even after adjustment for weight, menopausal status, smoking, and alcohol use.26
Conclusion
The diets shown to increase serum SHBG concentration are drawn from whole grains, vegetables, fruits, and legumes (beans, peas, and lentils), while eliminating meats, eggs, dairy products, and added oils. For women who choose to follow a vegan diet, it is also important to include a source of vitamin B12, such as a daily multivitamin or fortified breakfast cereals. Although some women regard such diets as austere at first glance, they generally prove acceptable with the support of cooking classes or dietetic counseling.26 The weight loss and marked reductions in serum cholesterol concentration that are typical on such diets may have the effect of reinforcing the new dietary pattern.27,28
Dr. Barnard is president of the Physicians Committee for Responsible Medicine in Washington, DC.
References
1. Goldin BR, et al. Effect of diet on excretion of estrogens in pre- and postmenopausal women. Cancer Res 1981;41:3771-3773.
2. Goldin BR, Gorbach SL. Effect of diet on the plasma levels, metabolism, and excretion of estrogens. Am J Clin Nutr 1988;48:787-790.
3. Shultz TD, Leklem JE. Nutrient intake and hormonal status of premenopausal vegetarian Seventh-day Adventists and premenopausal nonvegetarians. Nutr Cancer 1983;4:247-259.
4. Barbosa JC, et al. The relationship among adiposity, diet, and hormone concentrations in vegetarian and nonvegetarian postmenopausal women. Am J Clin Nutr 1990;51:798-803.
5. Adlercreutz H. Western diet and Western diseases: Some hormonal and biochemical mechanisms and associations. Scand J Clin Lab Invest 1990;201(Suppl):3-23.
6. Barr SI, et al. Vegetarian vs. nonvegetarian diets, dietary restraint, and subclinical ovulatory disturbances: Prospective 6-month study. Am J Clin Nutr 1994;60:887-894.
7. Prentice R, et al. Dietary fat reduction and plasma estradiol concentration in healthy postmenopausal women. J Nat Cancer Inst 1990;82:129-134.
8. Ingram DM, et al. Effect of low-fat diet on female sex hormone levels. J Natl Cancer Inst 1987;79:1225-1229.
9. Rose DP, et al. Effect of a low-fat diet on hormone levels in women with cystic breast disease. I. Serum steroids and gonadotropins. J Natl Cancer Inst 1987;78:623-626.
10. Boyar AP, et al. Response to a diet low in total fat in women with postmenopausal breast cancer: A pilot study. Nutr Cancer 1988;11:93-99.
11. Woods MN, et al. Low-fat, high-fiber diet and serum estrone sulfate in premenopausal women. Am J Clin Nutr 1989;49:1179-1183.
12. Goldin BR, et al. Estrogen excretion patterns and plasma levels in vegetarian and omnivorous women. N Engl J Med 1982;307:1542-1547.
13. de Ridder CM, et al. Dietary habits, sexual maturation, and plasma hormones in pubertal girls: A longitudinal study. Am J Clin Nutr 1991;54:805-813.
14. Belanger A, et al. Influence of diet on plasma steroid and sex plasma binding globulin levels in adult men. J Steroid Biochem 1989;32:829-833.
15. Barnard ND, et al. Diet and sex-hormone binding globulin, dysmenorrhea, and premenstrual symptoms. Obstet Gynecol 2000;95:245-250.
16. Moore JW, et al. Serum concentrations of total and non-protein-bound oestradiol in patients with breast cancer and in normal controls. Int J Cancer 1982;29:17-21.
17. Street C, et al. Inhibition of binding of gonadal steroids to serum binding proteins by non-esterified fatty acids: The influence of chain length and degree of unsaturation. Acta Endocrinol (Copenh) 1989;120:175-179.
18. Cassidy A, et al. Biological effects of a diet of soy protein rich in isoflavones on the menstrual cycle of premenopausal women. Am J Clin Nutr 1994;60:333-340.
19. Merskey H, Bogduk N, eds. Classification of Chronic Pain. 2nd ed. Seattle, WA: IASP Press; 1994:164-166.
20. Hansen SR, Deutch B. Dietary habits and menstrual distress. Näringsforskning 1990;34:140-146.
21. Benedetto C. Eicosanoids in primary dysmenorrhea, endometriosis and menstrual migraine. Gynecol Endocrinol 1989;3:71-94.
22. American College of Obstetrics and Gynecology. ACOG committee opinion: Premenstrual syndrome. Int J Gynaecol Obstet 1995;50:80-84.
23. Jones DY. Influence of dietary fat on self-reported menstrual symptoms. Physiol Behav 1987;40:483-487.
24. Hunter JE. n-3 fatty acids from vegetable oils. Am J Clin Nutr 1990;51:809-814.
25. Deutch B. Menstrual pain in Danish women correlated with low n-3 polyunsaturated fatty acid intake. Eur J Clin Nutr 1995;49:508-516.
26. Feskanich D, et al. Milk, dietary calcium, and bone fractures in women: A 12-year prospective study. Am J Publ Health 1997;87:992-997.
27. Barnard ND, et al. Acceptability of a therapeutic low-fat, vegan diet in premenopausal women. J Nutr Educ 2000; in press.
28. Barnard ND, et al. Adherence and acceptability of a low-fat, vegetarian diet among patients with cardiac disease. J Cardiopulmonary Rehabil 1992;12:423-431.
29. Barnard ND, et al. Effectiveness of a low-fat, vegetarian diet in altering serum lipids in healthy premenopausal women. Am J Cardiol 2000;85:969-972.
Funding of Reviewed Studies
Reference 1: National Breast Cancer Task Force (National Cancer Institute). Reference 2: National Cancer Institute. Reference 4: Callicott Foundation. Reference 6: British Columbia Medical Services Foundation. Reference 7: National Cancer Institute; National Institute of General Medical Sciences, National Institutes of Health, Department of Health and Human Services. Reference 8: Cancer Foundation of Western Australia. Reference 9: National Cancer Institute, American Institute for Cancer Research. Reference 11: National Institutes of Health and ACS. Reference 12: National Breast Cancer Task Force, USDA Human Nutrition Research Center on Aging at Tufts University. References 15, 27, 28, 29: Physicians Committee for Responsible Medicine. Reference 18: Ministry of Agriculture, Fisheries and Foods (UK) and National Institutes of Health; grant from National Cancer Institute. Reference 24: Procter and Gamble Company. Reference 25: Danish National Science Foundation. References 3, 5, 10, 13, 14, 16, 17, 19, 20, 21, 23: unknown.
June 2000; Volume 2; 41-44
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