Human and Clinical Nutrition

A Vegetarian Diet Rich in Soybean ProductsCompromises Iron Status in Young Students12

NING-SING SHAW,3 CHIA-JNG CHIN* AND WEN-HARN PANfDepartment of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan,Republic of China; *Graduate Institute of Home Economics, Private Chinese CulturalUniversity, Taipei, Taiwan, Republic of China; and ^Institute of BiomdicalSciences,Academia Sinica, Taipei, Taiwan, Republic of China

ABSTRACT The iron status of young Chinese Buddhistvegetarians (23 men and 32 women) and nonvegetarianstudents (20 men and 39 women from a medicalcollege) was investigated by dietary assessment of ironintake and hematological measurement of biochemicalindices including hemoglobin, plasma iron, transferrin,transferrin saturation and plasma ferritin. A characteristic of the vegetarian diet in this study was thereplacement of meat by soybean products. Results ofthe dietary assessment showed that the average irondensity of the diets ranged from 1.9 to 2.2 mg/MJ, withno difference between the vegetarian and nonvegetariandiets. Daily iron intake was similar in both vegetarianand nonvegetarian men. However, iron intake was significantly higher in female vegetarians than non-vegetarians, averaging 104 and 78% of the RDA,respectively. Results of blood analysis showed that, forboth sexes, the median plasma ferritin concentration ofthe vegetarians (male 47 /ig/L and female 12 /tg/L) wasabout half the level of the nonvegetarians (male 91 pg/Land female 27 nQ/L). Occurrence and risk of iron deficiency are more prevalent in vegetarians. Correlationbetween plasma ferritin concentration and years ofvegetarian practice in vegetarian men was marginallysignificant (r = -0.38, P = 0.077). We conclude that avegetarian diet that is rich in soybean products andrestricted in animal foods is limited in bioavailable ironand is not adequate for maintaining iron balance in menand women. J. Nutr. 125: 212-219, 1995.

INDEXING KEY WORDS:

soybean-rich, diet plasma ferritiniron status vegetarians humansiron intake

Vegetarian diets contain restricted amounts ofanimal products, especially fleshy foods, which areimportant sources of readily available heme iron andwhich enhance nonheme iron absorption (Hallberg1981). In addition, such diets include abundantamounts of cereals, legumes and vegetables containing components such as phytate, fibers and

0022-3166/95 $3.00 1995 American Institute of Nutrition.

soybean protein, which are inhibitory to nonhemeiron absorption (Cook et al. 1981, Hallberg and Rossander 1982, Schricker et al. 1982). Therefore, one ofthe nutritional problems related to nutrient adequacyin vegetarian diets is iron deficiency (AmericanDietetic Association 1993).

Caucasian vegetarians in developed countries areno more prone to nutritional anemia than the generalpopulation (American Dietetic Association 1993).Even though women are more susceptible to irondeficiency, women eating vegetarian diets for yearshad normal iron indices despite their small intake ofreadily available iron (Anderson et al. 1981). Mostsuch studies have been conducted with Seventh-DayAdventists or members of the Vegan Society of theUnited Kingdom, and both groups have a strong commitment to health and a well-informed approach tovegetarian diets. In contrast, studies of other socialgroups such as new vegetarians (Helman and Darton-Hill 1987) or ethnic groups such as immigrant Indians(Reddy and Sanders 1990) have suggested that somevegetarian populations may still be at risk for irondeficiency.

Few studies have examined the impact of Buddhistvegetarian diets on iron status. In general, Buddhistvegetarian diets are similar to the usual Chinese dietsin terms of meal pattern, cooking methods, choice ofrice as staple, and fruit and vegetable consumption(Pan et al. 1993). The major difference arises from thedoctrine that it is forbidden to kill living beings.Therefore, fleshy foods are completely excluded from

Supported by grant DOH80-69, Department of Health, Taiwan,Republic of China.

2The costs of publication of this article were defrayed in part bythe payment of page charges. This article must therefore be herebymarked "advertisement" in accordance with 18 USC section 1734solely to indicate this fact.

3To whom correspondence should be addressed.

5.Manuscript received 24 November 1993. Initial review completed 31 January 1994. Revision accepted 29 July 1994.

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VEGETARIAN DIET AND IRON STATUS 213

diets. Because soybean products are often substitutedfor animal products (Huang and Ang 1992), theprimary protein sources of vegetarians are rice andsoybean products (Pan et al. 1993). Several investigations have demonstrated that the percentage of ironabsorption from soybean and soy products is low inhumans (Cook et al. 1981, Lynch et al. 1984) and thatinclusion of soybean products in a diet is inhibitory toiron absorption (Hallberg and Rossander 1982, Lynchet al. 1985). However, the long-term effect of avegetarian diet rich in soybean products on ironstatus has not been directly evaluated in humans.Compared with the Seventh-Day Adventist diets(American Dietetic Association 1993), soybeanproducts were more important in the Buddhistvegetarian diets in this study, because soybeanproducts were included in the Buddhist diets ingreater quantities than whole grains, nuts, dried fruitsand legumes. The present study compared the intakeand status of iron in a group of Chinese Buddhistvegetarian students with a group of nonvegetarianstudents by using hemoglobin, plasma transferrin,plasma iron, transferrin saturation and plasma ferritinas the principle biochemical indices.

SUBJECTS AND METHODS

Subjects. The project was conducted from December 1990 to January 1991. Subjects were initiallyrecruited for the investigation of hemostatic and lipidprofiles in Buddhist vegetarians and nonvegetarians.The detailed description of recruitment, dietary assessment and blood collection was presented in aprevious report (Pan et al. 1993).

In brief, the subjects included 55 vegetarians (23men and 32 women) from Yuan-Guan BuddhistCollege, Chung-Li, Taoyuan, Taiwan, and 59 non-vegetarians (20 men and 39 women) from the Departments of Nursing and Medicine at the National Defense Medical School, Taipei, Taiwan. All subjectsmet the following requirements: age 2 y.All the women studied were nulliparous. Informedconsent forms were signed by all participants. Thestudy protocol was approved by the Institute of Bio-medical Sciences as ethical when the research proposal was reviewed. The characteristics of the subjects, including age, height, weight and use ofnutrient supplement, are listed in Table 1.

Dietary data. Subjects were served breakfast, lunchand dinner in the school dining hall, and dietaryintakes for each individual were assessed using a foodweighing method. All served foods were weighedbefore and after meals for three consecutive days ontwo occasions that were 1.5 mo apart. The number ofexchanges of various food groups was calculated according to the United States exchange system(American Dietetic Association 1986). The energyintake was calculated from the contents of carbohydrate, protein and lipid after proximate analysis (Panet al. 1993). Intakes of iron, vitamin C and crude fiberwere calculated by using food composition tables(Huang et al. 1978, Tung et al. 1961). The meannutrient intakes per day were calculated by averagingintakes for the 6 d. The dietary iron density is expressed as milligrams of iron per megajoule.

Blood analysis. Venous blood samples were collected from fasting subjects, using Vacutainers containing sodium heparin (Sherwood Medical, St. Louis,

TABLE 1Subject characteristics1

Male Female

Age, yHeight, cmWeight, kgBody mass index, kg/m2Duration of vegetarian diets,ySupplementation,

no. of usersMultivitaminsVitaminCVitaminBVitaminECalciumNonvegetarian

(n =>20)20.61.0171.74.1

62.7 3.721.3 1.2

052100Vegetarian

(n =23)22.64.4a

168.1 4.956.4 6.520.0 1.3a5.5

4.662000Nonvegetarian

(n =39)20.31.1

161.1 4.153.7 5.920.7 2.6

022000Vegetarian

(n -32)24.84.0b

158.5 6.150.4 8.020.1 2.8

6.7 6.242212

Values are means so. Superscripts indicate a significant difference between dietary groups within sex according to Student's test: aP