European Journal of Clinical Nutrition (2000) 54, 797±802 ß 2000 Macmillan Publishers Ltd All rights reserved 0954±3007/00 $15.00 www.nature.com/ejcn

Special postpartum dietary practices of Hong Kong Chinese women SM Chan1, EAS Nelson1*, SSF Leung1, PCK Cheung2 and CY Li3 1

Department of Paediatrics, The Chinese University of Hong Kong, Shatin, Hong Kong, Republic of China; 2Food and Nutritional Sciences Program, The Chinese University of Hong Kong, Shatin, Hong Kong, Republic of China; and 3Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong, Republic of China

Objective: A `ginger vinegar soup' and other special dietary practices have been traditionally recommended for postpartum Chinese women. This paper describes these practices in the ®rst 6 weeks postpartum, and details of the calcium and iron content of the `ginger vinegar soup'. Design and subjects: Results of this paper were generated from a longitudinal study on the nutritional status of Hong Kong Chinese postpartum women. `Ginger vinegar soup' samples were collected at the 2 week home visits. Calcium and iron content were measured by the combination of dry ashing method and atomic absorption spectrophotometry. Results were compared with other types of soup and food sources. A food frequency questionnaire was completed at the 6 week interview to assess the special dietary practices during this period. Results: Fifty-one subjects completed the food frequency questionnaires. Twenty-two ginger vinegar soup samples and six other soup samples were collected. Consumption of special food items such as ginger, pig's trotters, egg and chicken varied greatly among subjects. More poultry and similar amounts of egg were consumed by our subjects as compared with the Hong Kong general population. Chicken soup and ginger vinegar soup were commonly consumed. Median calcium and iron contents of the ginger vinegar soup were 4.65 and 0.84 mg=dl, respectively. This calcium content was higher than that of the other six soup samples, but was low as compared with other calcium-rich foods. Iron content of ginger vinegar soup was higher than that of the other six samples and was comparable to some iron-rich foods. Conclusions: Hong Kong Chinese postpartum women followed traditional dietary practices to different degrees. These practices were characterized by an increased poultry consumption. Iron content of ginger vinegar soup was comparable to some iron-rich foods. Descriptors: Chinese; postpartum; diet; calcium; iron European Journal of Clinical Nutrition (2000) 54, 797±802

Introduction Postpartum dietary habits vary greatly among different cultures. Some cultures, especially those in¯uenced by the concepts of the `hot ± cold system' or `yin ± yang balance', follow special dietary practices and food choices (Riordan, 1993; Mathews & Manderson, 1980). Due to the high physiological stresses of pregnancy and blood loss during delivery, the health status of postpartum women is considered to be `weak' from a traditional Chinese medicine perspective (Xuan & Li, 1990; Chang, 1974). Excessive blood loss during delivery is suggested to destroy the equilibrium between the `yin and yang' systems. Therefore, Chinese postpartum women are considered to be at a stage of Qi de®ciency and short of blood. It is thought that they can be easily attacked by `blood heat', `blood stasis', `heatevil' and `cold-wind', in which they may have signs of high fever, dizziness, rapid pulse, pale face, incessant bleeding or blood clots after delivery (Xuan & Li, 1990; Chang, *Correspondence: EAS Nelson, Department of Paediatrics, Prince of Wales Hospital, Shatin, N.T., Hong Kong, Republic of China. E-mail: [email protected] Guarantor: EAS Nelson. Contributors: SSF Leung and SM Chan initiated and designed the study. Most of the subject's recruitment, data collection, laboratory analysis and data analysis were performed by SM Chan. All authors contributed to the original manuscript and the subsequent revisions of the paper. Received 22 February 2000; revised 11 July 2000; accepted 19 July 2000

1974). As a result, traditional Chinese medicine stresses the importance of adopting special precautions and dietary practices in the ®rst month after delivery. During this period, the main goals of dietary practices for Chinese postpartum women are to enrich and nourish the blood, replenish Qi, dispel the `cold-wind' and relieve pain. Foods such as fruits and some kinds of vegetables, soy products, cold drinks that are regarded as `cold' should therefore be avoided. In contrast, foods that are able to remove `cold-wind', enrich blood and strengthen the internal organs should be frequently consumed. These foods include ginger, dates, chicken, pig's trotter, and internal organ meats, and they are therefore strongly recommended for Chinese postpartum women (Chang, 1974). Traditionally, a special dish composed of ginger, pig's trotter, eggs and sweet vinegar is prepared for the Chinese postpartum woman in Guangdong Province. The recommendation of consuming this special dish is common for Guangdong postpartum women. The traditional method of preparing this special dish is shown in Table 1. Not only the ingredients used, but the total time spent on preparation lead to its uniqueness. Usually, this dish is prepared 1 ± 2 months before delivery. The extended period for preparation may allow suf®cient time for the nutrients to dissolve into the sweet vinegar. Moreover, due to repeated reheating, the sweet vinegar is regularly re®lled to prevent the dish from drying out.

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Table 1 General practice for preparing the special disha Ingredients

Amounts in proportion

1. 2. 3. 4.

6.5 kg 3 kg 1.2 kg (approximately one) 500 g (approximately 10)

Ginger Bottled sweet vinegar Pig's trotter Boiled eggs

1 ± 2 months before delivery 1. 2. 3. 4.

Wash, peel and press ginger Stir fry ginger to reduce water content Put ginger into clay pot Add sweet vinegar at the level just covering ginger 5. Heat until boiling (about 2 ± 3 h in the ®rst cooking) 6. Reheat every 3 ± 7 days with occasional sweet vinegar re®lls

After delivery

7. Wash and boil pig's trotter and eggs 8. Add pig's trotter and eggs into another clay pot 9. Pour the soup prepared in step (6) into this clay pot and heat until boiling 10. Consume from the twelfth day after delivery onwards for about a month 11. Re®ll ingredients and reheat when necessary

a

Modi®ed from Lisa Yam's Health Food: Recipes for Pregnant Women (Fang, 1990).

Due to the acidic nature of the sweet vinegar, it is possible that some nutrient components such as calcium and collagen in the pig's trotters, and iron in the ginger and eggs are partly dissolved. The base consists of ginger, pig's trotter and eggs, and from this a soup is formed. This soup is called `ginger vinegar soup'. Although several studies have examined the dietary practices and milk composition of lactating women in different Chinese populations (Kneebone et al, 1985; Chen et al, 1997; Xiang et al, 1999), no data on the traditional special Chinese dietary practices and the nutrient contents of the `ginger vinegar soup' are available from the literature. Traditionally, Chinese postpartum women in Guangdong Province are advised to consume frequently both the ginger vinegar soup and the base, ie the ginger, eggs, and pig's trotters, in the early postpartum period. However, the frequency of consumption varies among different women depending on their personal preferences. Moreover, there is no mandatory combination in the consumption of this special dish. It can be served as a regular meal or as a snack. Women may consume the whole dish at a time. They may also choose to consume ginger, pig's trotters or eggs at a time, or drink the ginger vinegar soup only. Sometimes, the ginger vinegar soup may also be served with rice to stimulate appetite. Therefore, the special dish is not made over an easily de®ned period. Additional ingredients are added at irregular intervals and the soup pot is reheated at different time intervals. Other soups and drinks, such as a date tea prepared from soaking dates in boiling water, and a chicken wine prepared from cooking chicken with glutinous rice wine are also consumed by postpartum women. Special Chinese tonics composed of herbs and Chinese medicine are recommended to help restore the health status of women after delivery. Rapid economic development in Hong Kong is likely to have in¯uenced these traditional dietary practices, but the European Journal of Clinical Nutrition

extent of these changes is not known. This paper documents these traditional Chinese postpartum dietary practices in the ®rst 6 weeks postpartum, as part of a longitudinal study on the calcium and iron nutritional status of Hong Kong Chinese postpartum women. The results of calcium and iron content of ginger vinegar soup are also presented. Subjects and methods Subjects Results of this paper were generated from a longitudinal study on the nutritional status of Hong Kong Chinese postpartum women. Subjects were recruited in the postnatal ward of the Obstetrics and Gynaecology Department in the Prince of Wales Hospital between February and December 1998. Interviews were made at 0 week ( 7 days postpartum), 2 + 1 weeks (as home visits) and 6 + 1 weeks, 3 + 0.5 and 6 + 0.5 months postpartum. Basic personal and medical information were ®rst checked. Women who were healthy Hong Kong Chinese aged between 20 and 40 y, Hong Kong citizens, and who had delivered a full-term ( 37 weeks of gestation) healthy singleton infant, were included in the study. Those who were smokers and drinkers, had a medical history of metabolic bone diseases, were taking medication that could affect bone metabolism, had a medical history of haematological disorders and antenatal anaemia (haemoglobin level < 11 g=dl) at the time of booking were excluded. Since the primary aim of the whole study was to compare the calcium and the iron nutritional status of the formula-feeding mothers with that of the breastfeeding mothers (breastfed for  3 months) in Hong Kong, postpartum women who ful®lled the above criteria were ®rst approached by researchers to ask about their planned infant feeding practices. For breastfeeding mothers, they were further asked about the intended duration of breastfeeding. Only those who intended to exclusively breastfeed for  3 months were included. The de®nition of breastfeeding was based on Labbok's de®nition (Labbok & Krasovec, 1990). The purpose and nature of the study were explained to the mothers and informed written consent obtained for those who agreed to participate. The study protocol was approved by the Ethics Committee of The Faculty of Medicine, The Chinese University of Hong Kong. Assessment of special dietary practices Special dietary practices during the ®rst 6 weeks postpartum were assessed by administering a food frequency questionnaire (FFQ) at the 6 week interview. The questionnaire consisted of selected food items commonly consumed by Chinese postpartum women. Categorization of different types of special foods facilitated systematic reporting and recording by subjects and interviewer respectively. Bowls, cups and spoons were displayed to help recall. Description of portion sizes and the frequency of consuming a particular type of special food on a daily or weekly basis were also recorded. As there was a general increase in food intake from baseline to 2 weeks postpartum followed by a gradual decrease to a pre-pregnant level at around 6 weeks postpartum, the FFQ data were crosschecked with those of a 3-day dietary record at 0, 2 and 6 weeks interviews collected as part of the longitudinal study. If discrepancies occurred, subjects were further asked in detail to clarify these discrepancies.

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For the 3-day dietary record, a specially designed record form was mailed to subjects before the arranged follow-up. They were asked to record the type and the amount of all the foods and beverages consumed over the 3-day period prior to interview. During the interview, a food photo album which had been used in the 1995 Hong Kong Adult Dietary Survey (Leung et al, 1997) consisting of commonly consumed foods was shown to subjects. Bowls, plates, glasses and spoons of standardized portion size were shown simultaneously to help recall and quanti®cation of dietary intake. Cooking methods were also determined to estimate the amount of oil consumed. In addition, dietary practices, such as removal of chicken skin or drinking soup without consuming the base were asked to minimize bias in dietary estimation. Data were estimated using a computerized food table with food items compiled from Britain (McCance et al, 1978), China (Institute of Health, 1980), Taiwan (Tung et al, 1961), and the US (Church & Church, 1975. US Department of Health, 1972). Chemical analyses of some local Chinese foods from the government chemist, and product information from food manufacturers were also included. Daily food intake was expressed as number of g or ml per day. Mineral determination in the ginger vinegar soup Although ginger, eggs and pig's trotters are the main components of the special dish (Table 1), no attempt was made to analyse the nutrient contents of these food items since this can be estimated from the food composition tables. However, no data on the nutrient contents were available for the ginger vinegar soup. Therefore, in the present study, we performed nutrient analysis for the ¯uid component, ie the ginger vinegar soup, instead of the solid component, ginger, eggs and pig's trotter, which was unlike most other food analyses which focus on the analysis of the solid components. Food analyses of the ginger vinegar soup samples were not performed for all subjects due to the consideration of resources. Twenty-two samples were randomly collected at the 2 week home visit. A 100 ml sample of the soup was collected in a clean plastic bottle. Information on the method of preparation, amount of ingredients added, date of starting preparation of the dish, and total cooking time was recorded. However, the special dish was not made over an easily de®ned period. Additional ingredients were added at irregular intervals and the soup pot was reheated at different time intervals. Therefore, in the present study, the total amount of ingredients that had ever been added was used to calculate the amount of ingredients. In addition, total cooking time was taken as the number of hours used in the ®rst cooking plus the total number of hours used at subsequent recooking until sample collection. The total number of days of immersion was the number of days between the ®rst day of preparing the dish and the day of sample collection. Collected samples were brought to the laboratory and stored at 720 C until analysis. Dry ashing, followed by atomic absorption spectrophotometry (AAS), was used to determine the calcium and iron content of samples. All glassware used was soaked overnight in nitric acid to avoid contamination. Dry ashing followed the AOAC method 985.35 (AOAC International, 1995) with a few modi®cations. Of each collected sample, 10 ml were transferred in duplicate into crucibles and dried overnight at 100 C to minimize water content. Dried samples were then ashed at 550 C overnight until a uniform

ash was obtained. Ashed samples were dissolved in 5 ± 10 ml of 1 mol=l hydrochloric acid and rinsed with distilled water (dH2O). Dissolved samples were ®ltered with ashless ®lter paper and were diluted with dH2O to 50 ml in a volumetric ¯ask as stock solution for AAS determination (Hitachi Z8100, Japan). Total calcium and iron content were presented as mg=dl. Five different Chinese style soup samples (labelled as c1 ± c5) and one Western-style soup sample (labelled as w1) were collected from the canteen in the local Prince of Wales Hospital. The calcium and iron contents of these soups were analysed. As water content was high in the canteen soup samples, all soup samples were ®rst freeze dried to minimize the water content. Ashing procedures and the AAS determination followed the same protocols as those for the ginger vinegar soup samples. Both the calcium content and the iron content in other food sources were used for comparison (Holland et al, 1991; Wang & the Institute of Nutrition and Food Hygiene, Chinese Academy of Preventive Medicine, 1991).

799

Statistical analysis and data presentation Data were analysed with SPSS Version 8.0 for Windows (SPSS Inc, Chicago, IL, USA). The total amount of a particular type of special food over the 6 week period was calculated and converted as daily intake by dividing the total amount with 42 days. Data were expressed as g or ml per day. Three groups of subjects were categorized based on their infant feeding practices. They were the formula-feeding group, the breastfeeding groups for < 3 months and  3 months. One-way ANOVA test was used to test for differences among the three groups for the normally distributed data. Kruskal ± Wallis test and Mann ± Whitney U-test were used to compare the differences for data that were not normally distributed. Pearson correlation was used to examine the correlation of calcium and iron contents with other variables. The statistically signi®cant level was set at P < 0.05. As consumption of most special food items did not differ signi®cantly among the three groups, data were combined as one whole group for presentation and any signi®cant differences are speci®cally mentioned. Mean and standard deviation (s.d.) were used to express the normally distributed data, whereas median and interquartile range were presented for data that were not normally distributed. Results Descriptive data of subjects Sixty-four subjects (20 formula-feeding, 44 breastfeeding) were originally recruited in the study. Seventeen formulafeeding subjects and 34 breastfeeding subjects attended the 6 week interview and completed the questionnaires. The mean + s.d. age of subjects was 30.2 + 3.6 y and details of other descriptive parameters are shown in Table 2. Special food consumption over the ®rst 6 weeks postpartum The daily intake of special food items consumed by subjects during the ®rst 6 weeks postpartum is summarized in Table 3. Various types of special food were consumed, including different kinds of soups and drinks, ginger, pig's trotter, egg and chicken. Consumption of these special food items, as re¯ected by the wide interquartile range, varied greatly among subjects. European Journal of Clinical Nutrition

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800 Table 2 Descriptive data of subjects Mean + s.d. (n) Age (y) Gestational age (week) No. of pregnancies Parity Estimated blood loss at delivery (ml) Placental weight (g) Height (cm) Weight at baseline (kg)

30.2+ 3.6 (51) 39.8+ 1.3 (51) 2.0 + 1.0 (51) 1.5 + 0.6 (51) 257.8+ 141.9 (51) 537.5+ 98.4 (50) 157.6+ 5.2 (50) 60.7+ 7.9 (48)

Table 3 Daily intake of special food items in the ®rst 6 weeks postpartum (n ˆ 51, presented as ml or g per day) Food items Chicken soup (ml) Fish soup (ml) Date tea (ml) Chicken winea (ml) Special Chinese tonicb (ml) Pig's liver=kidney soup (ml) Ginger vinegar soup (ml) Chicken essencec (ml) Chicken, whole (g) Egg (g) Ginger (g) Pig's trotter with bone (g)

Median

25th percentile

75th percentile

95.2 28.6 19.1 0 0 0 6.2 0 95.2 23.8 5.3 10.7

9.5 0 0 0 0 0 0.4 0 38.1 11.9 0 0

190.5 83.3 66.7 2.4 0 0 19.1 11.7 285.7 35.7 14.3 21.4

a

Soup prepared from chicken and glutinous rice wine. bGlutinous rice wine and other special Chinese tonics made of herbs and Chinese medicine for postpartum women. cInstant bottled chicken essence.

Over the 6 weeks postpartum period, the most common soups or drinks consumed by subjects were chicken soup and ginger vinegar soup. Nearly 80% of subjects consumed these during the study period whereas date tea and chicken essence were consumed by half of the subjects. About a quarter of the subjects also consumed chicken wine and special Chinese tonics in the ®rst 6 weeks postpartum period (Figure 1). However, the consumption was more common in the formula-feeding group than in the breast-

feeding group. In contrast, the breastfeeding subjects showed signi®cantly (P < 0.05) higher amount of ®sh soup consumption than the formula-feeding subjects. The median (interquartile range) daily amount of ®sh soup consumed by the formula-feeding group was 0 (0 ± 21.4) ml=day, whereas it was 32.1 (3.6 ± 85.1) ml and 100 (38.1 ± 228.6) ml per day respectively in the breastfeeding group (< 3 months) and the breastfeeding group ( 3 months). Nearly all subjects had consumed chicken and egg, and over two-thirds of subjects consumed ginger and pig's trotter within the 6 weeks study period (Figure 1). The median (interquartile range) daily amount of chicken and egg consumed was 95.2 (38.1 ± 285.7) and 23.8 (11.9 ± 35.7) g=day, respectively in the ®rst 6 weeks postpartum period (Table 3). Calcium and iron contents in ginger vinegar soup Twenty-two samples were collected for food analysis. Table 4 summarizes the amount of different ingredients, number of cooking hours and number of immersion days for the preparation of this special dish. Great variation in the ingredients and preparation methods existed among the samples. Four main ingredients were used, ginger, egg, pig's trotter and sweet vinegar. Approximately 6048 g, 1500 g, 3629 g and 9072 ml of ginger, egg, pig's trotter and sweet vinegar were used, respectively, in the preparation of this special dish. The median number of cooking hours was 8.6 h and the median number of days of immersion was 59 days (Table 4). No correlation was observed between the calcium and iron content measured, amount of ingredients, number of cooking hours and number of days of immersion. Higher calcium and iron contents were observed in the ginger vinegar soup as compared with other canteen soup samples. The median (interquartile range) contents of calcium and iron were 4.65 (2.87 ± 6.30) and 0.84 (0.57 ± 1.05) mg=dl, respectively, in the ginger vinegar soup. The samples containing the highest calcium content were not

Figure 1 Percentage of subjects that had consumed chicken, egg, ginger, pig's trotter, and special soups and drinks. European Journal of Clinical Nutrition

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Table 4 Amount of ingredients and preparation methods of the special dish (n ˆ 22) Variables

Median

25th percentile

75th percentile

Ginger (g) Egg (g) Pig's trotter (g) Bottled sweet vinegar (ml) Number of cooking hours (h) Number of days of immersion (day)

6048 1500 3628.8 9072 8.6 59

4233.6 700 1814.4 6048 4.5 34

7257.6 2700 7257.6 9979.2 12.3 75

the ones containing the highest iron content. In the other canteen soup samples, the calcium content ranged from 0.86 to 3.66 mg=dl and the iron content varied from 0 to 0.14 mg=dl. Discussion The high percentage of subjects consuming different types of special food items suggests that the majority of subjects retain some traditional Chinese dietary practices during the ®rst few weeks postpartum. However, the great variation in the amount of consumption as re¯ected by the large range suggests that some women may be moving away from the traditional special dietary practices. Some subjects did not consume any of these special food items during the ®rst 6 week period. For most of our subjects, the special dish was not prepared by themselves. Rather, it was prepared by older family members, mainly their mothers or mother-inlaws. It is thus likely that the method and skills of preparing the special dish may be gradually lost. The main focus of the present study was to describe the characteristics of the traditional special Chinese dietary practices. Although we did not anticipate any major differences in these dietary practices between the formula-feeding group and the breastfeeding group, our results showed that the ®sh soup consumption was higher in the breastfeeding subjects as compared to that of the formula-feeding subjects. Moreover, there was a dose ± response effect with the breastfeeding group ( 3 months) consuming the most. This result may be due to the traditional Chinese belief that ®sh soup is able to promote breast milk production. Whether the greater ®sh soup consumption can stimulate more milk production and lengthen the duration of breastfeeding or whether the breastfeeding subjects tended to consume more ®sh soup based on their perception that the ®sh soup can stimulate milk supply remain to be identi®ed. Based on the hypothesis that the bone calcium in pig's trotter, and the iron in egg yolk and ginger may dissolve into sweet vinegar, we initially speculated that the special dish may help restore both the calcium and the iron status of women after delivery. Moreover, a very hot stove in the ®rst cooking followed by reheating at a lower temperature at regular time intervals was used in the preparation of this special dish (Table 1). We speculated that this process of repeated reheating and boiling may facilitate the release of the nutrients, eg minerals and collagen, into the sweet vinegar. In the present study, the calcium content in the ginger vinegar soup was high as compared with other canteen soup samples. However, the level was only low or moderate as compared to other calcium-rich foods. In contrast, the iron content in the ginger vinegar soup not only was higher that the canteen soup samples, but also was

comparable to some iron-rich food sources. The collagen content was not measured in the present study. However, we observed that the nature of the ginger vinegar soup changed from ¯uid at the beginning of preparation to a viscous consistency at the later stage of consumption. The possibility that the collagen from pig's trotters may dissolve into the sweet vinegar thus cannot be excluded, but further investigation is needed to con®rm this. Compared with the mean daily intake of the Hong Kong general population, our subjects consumed more poultry (95.2 vs 59 g=day) and similar amounts of egg (23.8 vs 19 g=day) during the ®rst 6 weeks postpartum. The similar level of egg consumed by our subjects was unexpected since previous study focused on a sample of Hong Kong breastfeeding mothers showed that 50 g=day of egg was consumed in the ®rst 6 weeks (Chen et al, 1997). Data suggested that the iron intake of our subjects were comparable to that of the US Recommended Daily Allowance (RDA) and Hong Kong females of similar age (unpublished). For Hong Kong Chinese postpartum women whose pre-pregnant daily iron intake is around 15 mg and haem iron is the main iron source (Leung et al, 1997), the importance of these special dietary practices may diminish due to the change of dietary pattern resulting from urbanization. No data, to the best of our knowledge, on postnatal iron intake for rural Chinese postpartum women are available from the literature. Previous studies have showed that the daily total iron intake of rural Chinese women is around 20 ± 30 mg=day, of which non-haem iron is the main iron source (Root et al 1999; Ge et al, 1995). Although the consumption of the special dish is common for Guangdong postpartum women, the increased consumption of other haem iron sources eg poultry, meat and eggs, during the early postpartum period is commonly practised by the rural Chinese women of other provinces, eg Chongqing (Chen et al, 1997). Traditional special dietary practices may be particularly important for restoring postpartum health status in rural populations where diets may be less varied. As some special food items are good sources of iron, together with the comparably high iron content in the ginger vinegar soup, these special dietary practices may have a role in promoting iron absorption and restoring iron stores in women after delivery. Organic acids in the sweet vinegar may provide an acidic environment which favours the absorption of non-haem iron (Bothwell et al, 1989). A previous study examining the iron status of Hansa lactating women in the Kano State of Nigeria also suggested that yajin jego, `pepper prepared for lactating women', may enhance the healing process and prevent infection in lactating mothers (Gwarzo et al, 1994). The ginger in the ginger vinegar soup may also have similar effects because similar medicinal uses of pepper and ginger, including the increasing blood ¯ow, removal of excessive gas in the body and the stimulation of appetite, have been stated (Wee & Hsuan, 1990). Several limitations should be considered in our present study. First, due to the regular addition of different ingredients after each consumption, the method used for recording the amount of ingredients used in the special dish was limited to the maximum amount of ingredients that had ever been added. This may account for the weak correlation between calcium and iron contents measured, amount of ingredients, number of cooking hours and number of days of immersion. Second, only a limited number of samples (n ˆ 22) and types of canteen soup samples (n ˆ 6) were

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collected for mineral determination, and only one sample was collected for each type of canteen soup. Errors in sample collection and sampling should therefore be considered. Finally, only calcium and iron contents of the ginger vinegar soup were measured in the present study. The content of phosphorus, which is a major dietary factor interacting with dietary calcium, was not measured. Therefore, the calcium to phosphorus ratio of these samples remains unknown. Only the total iron content of samples was measured, and thus the proportion of ferric and ferrous ions in the soup samples, and their effects on iron absorption require further investigation. Although the role of the acidic environment in ginger vinegar soup in enhancing non-haem iron absorption was suggested, iron absorption studies would be helpful to con®rm this. It would be valuable if the calcium absorption ef®ciency of the ginger vinegar soup could be measured, as increased calcium absorption has been found in an acid medium (Allen, 1982). Conclusions Although the majority of our subjects followed traditional practices to some degree, the wide range of consumption of special food items suggested that there was considerable variation in the enthusiasm with which this was done. Our data showed that an increased amount of poultry was consumed in the early postpartum period. In addition, ginger, pig's trotter and ginger vinegar soup were commonly consumed by Hong Kong Chinese postpartum women. Whether the consumption of these iron-rich food items together with the comparably high iron content measured in the ginger vinegar soup bene®ts the recovery of health status of postpartum Chinese women remains to be identi®ed. Acknowledgements ÐWe thank Jannis WS Yau and Roselle HY Li for their assistance in recruiting and scheduling subjects; Jessie PK Lee, Richard TC Wong, CF Chow for their suggestions and laboratory assistance; and all the subjects for their commitment in the study. SM Chan was supported by a research studentship from the Research Grants Council, Hong Kong.

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