Maternal nutrition, infants and children

The effect of DASH diet on pregnancy outcomes in gestational diabetes: a randomized controlled clinical trial

Abstract

Background/Objectives:

The current study was performed to investigate the effects of the Dietary Approaches to Stop Hypertension (DASH) eating plan on pregnancy outcomes in pregnant women with gestational diabetes mellitus (GDM).

Subjects/Methods:

This randomized controlled clinical trial was performed among 52 women diagnosed with GDM. Participants were randomly assigned to consume either the control (n=26) or the DASH diet (n=26) for 4 weeks. The control diet was designed to contain 45–55% carbohydrates, 15–20% protein and 25–30% total fat. The DASH diet was rich in fruits, vegetables, whole grains and low-fat dairy products, and contained lower amounts of saturated fats, cholesterol and refined grains with a total of 2400 mg/day sodium. The numbers of women who commenced insulin therapy after dietary intervention, the mode of delivery and prevalence of polyhydramnios were assessed. The length, weight and head circumference of infants were measured during the first 24 h after birth.

Results:

Whereas 46.2% of women in the DASH diet needed to have a cesarean section, this percentage for the control group was 80.8% (P=0.01). The percentage of those who needed to commence insulin therapy after intervention was also significantly different between the two groups (23% for DASH vs 73% for control group, P<0.0001). Infants born to mothers on the DASH diet had significantly lower weight (3222.7 vs 3818.8 g, P<0.0001), head circumference (34.2 vs 35.1 cm, P=0.01) and ponderal index (2.50 vs 2.87 kg/m3, P<0.0001) compared with those born to mothers on the control diet.

Conclusions:

In conclusion, consumption of DASH diet for 4 weeks among pregnant women with GDM resulted in improved pregnancy outcomes.

Introduction

Gestational diabetes mellitus (GDM) has been defined as onset of glucose intolerance during pregnancy.1 This condition usually disappears during the puerperium.2 The prevalence of GDM ranges from 1 to 14% depending on different screening methods, diagnostic criteria and the population screened.3 In Iran, it has been reported that 4.7% of pregnant women are affected.4 GDM has been associated with macrosomia, birth trauma, shoulder dystocia and higher rates of cesarean section,5 as well as with metabolic disturbances in the offspring6 and with an increased risk of developing type II diabetes in maternal later life.7

To improve pregnancy outcomes among patients with GDM, several strategies including lifestyle modification, dietary intervention and, if necessary, using oral hypoglycemic agents and insulin injections have been applied.8 In previous reviews, consumption of a low-glycemic index (GI) diet has been reported to result in improved pregnancy outcomes in GDM patients.9, 10 In a randomized controlled clinical trial, Moses et al.11 showed that adherence to a low-GI diet compared with a high-GI diet among pregnant women with GDM resulted in a decreased requirement for insulin injections. However, consumption of a low-GI eating pattern compared with a high-fiber diet in GDM patients did not affect newborn birth weight, prevalence of macrosomia, insulin treatment or other pregnancy outcomes.12

The Dietary Approaches to Stop Hypertension (DASH) eating plan has originally been suggested for the control of hypertension;13 however, its beneficial effects have also been documented in type II diabetes14 and metabolic syndrome.15 The DASH diet is a low-GI low energy-dense diet that contains high amounts of dietary fiber, phytoestrogens, potassium, calcium, magnesium and folic acid,16 and the beneficial effects of most of these components on pregnancy outcomes have earlier been shown.9, 12 Although the effects of DASH diet on several metabolic conditions have been previously studied, we are aware of no study examining the effects of DASH diet on pregnancy outcomes in GDM. Therefore, the current study was performed to investigate the effects of the DASH eating plan on pregnancy outcomes in pregnant women with GDM.

Subjects and methods

Participants

This two-arm parallel randomized controlled clinical trial was carried out in Kashan, Iran, during January 2013 to June 2013. To estimate the required sample size, we used the appropriate formula, where the type one (α) and type two errors (β) were considered as 0.05 and 0.20 (power=80%), respectively. In addition, birth weight was defined as the key variable and based on earlier studies,17 and the s.d. of this variable was 90 g. We considered 75 g as the significant difference in mean birth weight between the two groups. Therefore, the required sample size was estimated to be 21 subjects in each group. Primigravida pregnant women aged 18–40 years diagnosed with GDM by a 100-g oral glucose tolerance test at 24–28 week gestation were recruited in this study. Gestational age was assessed from the date of last menstrual period and concurrent clinical assessment.18 Pregnant women without a previous diagnosis of glucose intolerance were screened for GDM by two procedures. First, a 50 g glucose challenge test was used as preliminary screening. Individuals with 1-h plasma glucose concentrations of >140 mg/dl were then asked to participate in a 100 g oral glucose tolerance test. Diagnosis of GDM was based on the criteria as set by the American Diabetes Association:19 those whose plasma glucose levels met two of the following criteria were considered as having GDM: fasting >95 mg/dl, 1-h 180 mg/dl, 2-h 155 mg/dl and 3-h 140 mg/dl. A total of 980 pregnant women attending maternity clinics affiliated to Kashan University of Medical Sciences, Kashan, Iran, were screened for GDM. Finally, 58 pregnant women met the inclusion criteria (912 women were excluded because of not having GDM and 10 women were excluded because of the diagnosis of GDM class A2 that needed insulin therapy: fasting plasma glucose >105 and blood sugar 2-h postprandial >120 mg/dl). We excluded those with a previous glucose intolerance/GDM diagnosis, premature preterm rupture of membrane, placenta abruption, pre-eclampsia, requiring to commence insulin therapy during intervention, complete bed rest, hypothyroidism, urinary tract infection, smoking and kidney or liver diseases, as well as those taking estrogen therapy. A total of 58 pregnant women were recruited in the study and after stratification for preintervention body mass index (BMI; <30 and 30 kg/m2) and weeks of gestation (<26 or 26 weeks), they were randomly assigned to consume the control (n=29) or DASH diet (n=29). Random assignment was done using computer-generated random numbers. The study was conducted according to the guidelines laid down in the Declaration of Helsinki. The ethical committee of Kashan University of Medical Sciences approved the study (No: P/29/5/1/4139) and informed written consent was obtained from all participants.

Study design

Participants were randomly assigned to consume the control or DASH diet for 4 weeks. They were asked not to alter their routine physical activity, as well as not to receive any antihyperglycemic or lipid-lowering medications during the 4-week intervention. All pregnant women were also consuming 400 μg/day folic acid from the beginning of pregnancy and 50 mg/day ferrous sulfate as well as multivitamin–mineral supplements from 20 weeks of gestation. Compliance with the consumption of diets was monitored once a week through phone interviews. The compliance was also double-checked by the use of 3-day dietary records completed throughout the study. The dietary records were based on estimated values in household measurements. Participants were requested to complete three 1-day dietary records (2 week days and 1 weekend day) throughout the study. To obtain nutrient intakes of participants based on these 3-day food diaries, we used Nutritionist IV software (First Databank, San Bruno, CA, USA) modified for Iranian foods.

Diets

The control diet was designed to contain 45–55% carbohydrates, 15–20% protein and 25–30% total fat. The calorie content and protein composition of the DASH diet was similar to the control diet; however, the DASH diet was rich in fruits, vegetables, whole grains and low-fat dairy products, and low in saturated fats, cholesterol, refined grains and sweets. The amount of sodium intake was 2400 mg per day.15 An example of the DASH diet based on 2000 kcal has been provided in Table 1.

Table 1 Constituents of the DASH and control diets used in the studya

Assessment of maternal anthropometric measures

Maternal anthropometric measurements were assessed at baseline and after 4 weeks of intervention by trained midwifes. The prepregnancy weight and height were taken from the existing records of patients in the clinic. At baseline and after 4 weeks of intervention, body weight was measured in an overnight fasting status without shoes in a minimal clothing state using a digital scale (Seca, Hamburg, Germany) to the nearest 0.1 kg. Height was measured using a non-stretched tape measure (Seca) to the nearest 0.1 cm. BMI was calculated as weight in kg divided by height in meters squared.

Assessment of pregnancy outcomes

Although the intervention was done for 4 weeks, all participants were followed until delivery. They were called once a week to ask whether they have started insulin injections after dietary intervention. Mode of delivery (cesarean section or vaginal delivery) was also recorded for all participants. Polyhydramnios was diagnosed with sonographic estimation method. Length and weight of the infants were measured using standard methods (Seca 155 Scale) during the first 24 h after birth and were recorded to the nearest 1 mm and 10 g, respectively. Macrosomic babies were defined as those with a birth weight of >4000 g.20 The head circumference of the infants was measured to the nearest 1 mm with a Seca girth measuring tape. We also determined the 5 min Apgar score of the infants as another measure of pregnancy outcome. The ponderal index (kg/m3) of the infant was calculated. The need for cesarean section in study participants was determined by the study obstetrician based on estimated fetal weight, pelvic exam and other indications of cesarean section including malpresentation, fetal distress, dystocia and failure to progress of labor.

Assessment of plasma glucose

Fasting blood samples (5 ml) were taken at baseline at Kashan reference laboratory in an early morning after an overnight fasting. Plasma glucose levels were quantified using glucose oxidase/peroxidase (GOD–POD) method with commercially available kits (Pars Azmoon Co, Tehran, Iran).

Statistical analysis

To ensure the normal distribution of variables, histogram and Kolmogorov–Smirnov tests were applied. Independent samples Student’s t-test was used to detect differences between groups. This test was applied for comparison of changes between the two groups. Distribution of participants in terms of categorical variables was examined using the χ2 test. To determine whether the effect of DASH diet was independent of prepregnancy BMI, maternal fasting plasma glucose levels at study baseline and maternal age, we applied analysis of covariance. P<0.05 was considered as statistically significant. All statistical analyses were done using the Statistical Package for Social Science version 17 (SPSS Inc., Chicago, IL, USA).

Results

Among individuals in the control diet, three women (premature preterm rupture of membrane (n=1), needed to commence insulin therapy during intervention (n=1) or pre-eclampsia (n=1)) were excluded. The exclusions in the DASH diet were of three women (pre-eclampsia (n=1), placenta abruption (n=1) and complete bed rest (n=1)). Finally, 52 participants (control (n=26) and DASH diet (n=26)) completed the trial (Figure 1).

Figure 1
figure1

Summary of patient flow.

Mean age, prepregnancy weight and BMI were not statistically different between the two groups (Table 2). Baseline weight and BMI as well as post-intervention means of these variables were not significantly different between women in the DASH group as compared with those in the control group.

Table 2 General characteristics of the study participantsa

Based on the 3-day dietary records that participants provided throughout the study, no statistically significant difference was seen between the two groups in terms of dietary intakes of energy; however, significant differences were found in dietary intakes of saturated fatty acids, polyunsaturated fatty acids, cholesterol, dietary fiber, simple sugar, sodium, potassium, magnesium, calcium and vitamin C between the two groups (P<0.05 for all; Table 3).

Table 3 Dietary intakes of study participants throughout the interventiona

Consumption of the DASH eating pattern, as compared with the control diet, resulted in better pregnancy outcomes (Table 4). Although 46.2% of women in the DASH diet needed to have a cesarean section, this percentage for the control group was 80.8% (P=0.01). The percentage of those who needed to commence insulin therapy after intervention was also significantly different between the two groups (23% for DASH group vs 73% for control group, P<0.0001). No significant difference in mean gestational age was found when comparing the DASH and control diets. Prevalence of polyhydramnios was not significantly different between the two groups. Consumption of the DASH diet led to a significant reduction in the birth of macrosomic infants compared with the control diet (3.8 vs 38.5%, P=0.002). Infants born to mothers in the DASH diet had significantly lower weight (3222.7 vs 3818.8 g, P<0.0001), head circumference (34.2 vs 35.1 cm, P=0.01) and ponderal index (2.50 vs 2.87, P<0.0001) compared with those born to mothers in the control diet (Table 5). The influence of the DASH diet on pregnancy outcomes remained significant even after controlling for prepregnancy BMI (P<0.0001 for weight and P=0.03 for head circumference of the newborns, and P<0.0001 for ponderal index). Further adjustment for maternal fasting plasma glucose at study baseline did not influence the findings (P<0.0001 for weight and P=0.03 for head circumference of the newborns, and P=0.001 for ponderal index). When we adjusted the analysis for maternal age, our findings did not change. We did not find a significant difference in mean length and Apgar score of the newborns when comparing the DASH and control diets.

Table 4 The effect of DASH eating pattern on pregnancy outcomesa
Table 5 The effect of DASH eating pattern on birth size of the newbornsa

Discussion

Our findings revealed that consumption of DASH eating pattern for 4 weeks among pregnant women with GDM resulted in a decreased rate of cesarean section, reduced need to commence insulin therapy after intervention as well as lower rates of macrosomic babies. Mean weight, head circumference and ponderal index of infants born to mothers in the DASH diet were significantly lower compared with those born to mothers in the control diet. To our knowledge, this is the first study reporting the effect of DASH eating pattern on pregnancy outcomes of pregnant women with GDM.

Gestational diabetes is associated with several adverse pregnancy outcomes.7, 8, 21, 22 The current study showed that consumption of DASH diet in pregnant women with GDM resulted in a decreased rate of cesarean section compared with the control diet. Several factors including older maternal age, obesity, parity and ethnicity23 along with maternal vitamin D status has been associated with cesarean delivery.24 Earlier studies have shown the high rates of cesarean delivery in GDM patients despite well controlling of maternal blood glucose during pregnancy.25, 26 In total, the rate of cesarean section in Iran is high; such that in normal pregnant women without GDM, its prevalence has been reported to be 84% in private hospitals and 47% in university-affiliated hospitals in Tehran.27 Among those with GDM, this rate is particularly high. In two available reports, it has been reported that almost 90% of pregnant women with GDM gave birth by cesarean delivery.28, 29 Delivery by cesarean section has been associated with increased short-term neonatal morbidity as well as increased risk for allergy and asthma, childhood leukemia and testicular cancer and type I diabetes in later life.30 Recent studies have shown a significant association between low levels of serum calcium31 and vitamin D32 and increased risk of cesarean section. In the current study, dietary intake of calcium and magnesium in the DASH diet was 50% higher than that in the control diet. Dietary vitamin C and β-carotene content of DASH diet was 100% greater than the control diet. Mechanisms underlying the association between calcium, magnesium, vitamin C and β-carotene deficiency and increased risk of cesarean section remain largely obscure. Several studies have shown that magnesium,33 vitamin C34 and β-carotene35 supplementation can decrease adverse obstetric outcomes and reduce risk of cesarean section.36 In addition, higher rate of cesarean section in the control group in our study might be attributed to maternal hypertension at the end pregnancy.

We showed that DASH diet could significantly decrease the number of women who needed to commence insulin therapy. Earlier studies in Iran have shown that obstetrics and gynecologists recommend insulin therapy in GDM patients at most times to reduce the incidence of maternal and fetal complications.28, 37 In a study by Moses et al.,11 consumption of a low-GI diet as compared with a high-GI diet among women with GDM effectively reduced the number of women needing to use insulin. Consumption of a low-GI eating plan compared with the conventional diet from week 28 of gestation until delivery improved 2-h postprandial glucose levels among pregnant women with GDM or impaired glucose tolerance.38 Furthermore, improvement in insulin sensitivity following the adherence to DASH diet was seen in overweight people.39 Such findings have also been reached among healthy individuals40 as well as in patients with metabolic syndrome41 who consumed DASH diet for 6 months. Several mechanisms can explain the beneficial effects of the DASH dietary pattern on the need to commence insulin therapy in this study. For instance, dietary intake of simple sugar in the DASH diet in our study was about half the control diet, whereas its dietary fiber content was 50–100% more than the control diet. Earlier studies have indicated that high-sucrose diet could increase plasma glucose and insulin resistance.42 The higher content of arginine in the DASH diet in our study might also explain its effects on reducing the need for insulin. Improvements in insulin resistance following arginine intake might have resulted from increased nitric oxide production.43 High dietary magnesium and calcium content of the DASH diet might also provide further reasons for its effects.44

We found that adherence to the DASH diet in pregnant women with GDM resulted in a decreased number of macrosomic babies. This diet led to a lower mean of weight and head circumference of the newborns and ponderal index, but did not affect the length and Apgar score of the infants. Several studies have shown higher mean birth weight, greater number of large for gestational age birth and macrosomic babies as pregnancy outcomes in pregnant women with GDM.45, 46 In a study by Moses et al.,17 consumption of low-GI diet, as compared with high-GI diet, in pregnant women with GDM resulted in birth of lighter infants (P=0.05), lower birth centile (P=0.005) and lower prevalence of large for gestational age (P=0.01). The difference in mean birth weight between the two groups in the current study was almost 600 g. This is much lower than that obtained in another study that did the intervention with a low-GI diet.47 Clapp et al.47 in a longitudinal study showed that adherence to low-GI diet compared with high-GI diet from 8 weeks of gestation to delivery among pregnant women was associated with a decrease of 1000 g in mean birth weight. The same results have also been reported by others.48 Several mechanisms might explain the significant effects of DASH diet on pregnancy outcomes. Reduced maternal hyperglycemia among women in the DASH group compared with those in the control group as well as the low number of women who commenced insulin therapy after intervention in the DASH group can lead to reduced fetal hyperglycemia and resultant reduced fetal hyperinsulinemia that would in turn lead to a lower birth weight.49, 50 Maternal hyperglycemia prompts fetal hyperinsulinemia particularly during the second half of gestation that in turn stimulates excessive somatic growth.50

Several limitations must be taken into account when interpreting our findings. First, the duration of dietary intervention in this study was short. We were unable to continue the diets for more than 4 weeks because of the special condition of pregnant women. Long-term interventions might lead to greater changes. However, it must be kept in mind that participants in the current study were pregnant women who were concerned that dieting could have a negative impact on their babies. This could result in low compliance with the dietary intervention. Therefore, we could not continue the intervention until delivery. Furthermore, it must be kept in mind that GDM could be diagnosed between weeks 24 and 28 of pregnancy. As we wanted to examine the effect of DASH diet on pregnancy outcomes in GDM patients, we chose to enroll the patients at this time point. Recruitment of subjects later than this could result in low compliance to the diets because of the reason mentioned above. Second, we did not assess the compliance to the DASH diet using a biomarker. Totally, finding appropriate biomarkers for dietary patterns is a new field of research and we are aware of no definite biomarker that can reflect adherence to the DASH diet. Future studies might use urinary sodium excretion as a possible biomarker for assessing adherence to the DASH diet. Third, we did not assess the effects of DASH diet on other pregnancy outcomes including neonatal glucose levels, respiratory distress syndrome and hyperbilirubinemia.

In conclusion, consumption of DASH eating pattern for 4 weeks among pregnant women with GDM resulted in better pregnancy outcomes. Further studies about the potential mechanisms of actions are required.

Change history

  • 04 May 2020

    Editor's Note: The Co-Editors-in-Chief are currently investigating this article as concerns have been raised about integrity of the clinical trial reported here. There is also an ongoing investigation by the Iranian National Committee for Ethics in Biomedical Researches. Further editorial action will be taken as appropriate once the investigation into the concerns is complete and all parties have been given an opportunity to respond in full.

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Acknowledgements

The present study was supported by a Grant (No. 91104) from the Vice-Chancellor for Research, KUMS, Kashan, Iran. We thank the staff of Naghavi and Shaheed Beheshti Clinics (Kashan, Iran) for their assistance in this project.

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Correspondence to A Esmaillzadeh.

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Contributors: ZA conducted the study, carried out the statistical analysis, wrote the manuscript and contributed in the interpretation of the findings; ZT supervised the study; MS supervised the study and assisted in writing the manuscript; AE contributed in conception and study design and advised on statistical analyses, contributed in drafting the manuscript and assisted in interpretation of the findings. All authors approved the final version of the manuscript.

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Asemi, Z., Samimi, M., Tabassi, Z. et al. The effect of DASH diet on pregnancy outcomes in gestational diabetes: a randomized controlled clinical trial. Eur J Clin Nutr 68, 490–495 (2014). https://doi.org/10.1038/ejcn.2013.296

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Keywords

  • DASH
  • pregnancy outcomes
  • GDM
  • infant

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