A Phytosterol-Enriched Spread Improves Lipid Profile and Insulin Resistance of Women with Gestational Diabetes Mellitus: A Randomized,Placebo-Controlled Double-Blind Clinical Trial

Abstract

Background:

Gestational diabetes mellitus (GDM) has become a serious health risk among pregnant women throughout the world. Phytosterol-enriched margarines are capable of lowering total cholesterol (TC) and low-density lipoprotein (LDL), but little is known about its effects on GDM. We aimed to examine the effects of daily consumption of a phytosterol-enriched spread on insulin resistance and lipid profile in pregnant GDM women.

Methods:

Pregnant women suffering from GDM in their second trimester were recruited and randomly assigned to consume a margarine spread either with or without phytosterols daily for 16 weeks. Serum lipid profile and glucose and insulin metabolisms were assessed at week 0 (baseline) and week 16 (end of trial).

Results:

After 16 weeks, levels of triacylglycerol, TC, and LDL were significantly decreased, while high-density lipoprotein was significantly increased, compared with the baseline in the phytosterol group. In addition, in the same treatment group, glucose metabolic parameters, including fasting plasma glucose, serum insulin levels, the quantitative insulin check index, homeostasis model of assessment of insulin resistance, and β-cell function, were also significantly improved.

Conclusion:

Daily consumption of a phytosterol-enriched spread improved insulin resistance and lipid profile in women with GDM.

Introduction

Gestational diabetes mellitus (GDM) is a condition that occurs in pregnancy and commonly associates with insulin resistance and glucose intolerance.¹ Women affected by GDM usually do not present any diabetic symptoms and are only diagnosed with GDM during the second trimester of pregnancy. GDM is associated with maternal diabetic symptoms similarly seen in type 2 diabetes mellitus (T2DM), such as insulin resistance, elevated serum levels of total cholesterol (TC), and low-density lipoprotein (LDL), which usually only manifest during pregnancy, but could also result in abnormal fetal development.^2,3 It was estimated that as high as 20% of GDM patients even suffer elevated risk of long-term diabetes after pregnancy.^4,5

Phytosterols are structurally similar to cholesterols and, therefore, are able to compete with cholesterols for the inclusion into mixed micelles in the gut, which in turn result in lowered serum cholesterol concentrations.⁶ Although phytosterols have been found to exhibit cholesterol-lowering properties as early as in the 1950s,^7,8 it is only later in the 1990s that their cholesterol-lowering potential was discovered again.^9

–12 Margarine spreads enriched in phytosterols serve as a good vehicle to solubilize phytosterols, and even a small amount added was found to be able to markedly reduce serum cholesterols.^13

–17 Moreover, phytosterol-enriched spreads even exhibited beneficial effects in T2DM patients. In a randomized controlled trial, a phytosterol-enriched spread was found to be effective in lowering TC and LDL of T2DM patients and might decrease the elevated risk of cardiovascular disease in type 2 diabetes.¹⁸

To the best of our knowledge, there has been no study conducted to investigate the effects of a phytosterol-enriched spread on insulin resistance and lipid profile of pregnant GDM women. Considering the resemblance in symptoms between T2DM and GDM, we speculated that phytosterol-enriched spread as food supplement may improve maternal diabetic symptoms in pregnant GDM women as well. We, therefore, conducted this randomized, placebo-controlled, and double-blind clinical trial, with the aim to assess whether daily consumption of a phytosterol-enriched spread could alleviate diabetic symptoms, such as glucose and insulin metabolisms, in particular, in pregnant GDM patients.

Subjects and Methods

Ethics statement

The study was conducted according to the guidelines stated in the Declaration of Helsinki and was approved by the Ethics Committee of Cangzhou Central Hospital. All participants were fully aware of the potential risks of early GDM screen and signed informed written consent forms before joining the study and agreed with our anonymous data utilization policy.

Participants

This clinical trial was conducted in Cangzhou Central Hospital, from May 2011 to April 2015. A total of 248 pregnant women between the age of 25 and 34 years, who were carrying singleton pregnancy and diagnosed with GDM at the onset of their second trimester (13 weeks), were initially recruited for the study. Diagnostic criteria of GDM among the pregnant women, adapted from the American Diabetes Association guidelines,¹⁹ were as follows: fasting plasma glucose (FPG) ≥100 mg/dL, 1 h oral glucose tolerance test (OGTT) ≥180 mg/dL, and 2 h OGTT ≥155 mg/dL. Exclusion criteria of the study were as follows: history of diabetes, preeclampsia, eclampsia, hypo- and hyperthyroidism, urinary tract infection, multiparity, maternal hypertension, liver, kidney or renal disease, those requiring insulin therapy during the study, and those who consumed margarine or butter during the previous 6 months. Based on the above criteria, a total of 26 participants were excluded.

Randomized study design

A total of 222 pregnant GDM women were eventually eligible to participate in the rest of the study. Using a permuted-block randomization method stratified according to their baseline 1 h OGTT results, all participants in their second trimester were randomly and evenly assigned to consume two servings (10 g per serving) of either regular margarine spread as placebo or phytosterol-enriched margarine spread, with one serving at breakfast and the other one at dinner, on a daily basis for a period of 16 weeks. Each 10 g serving of phytosterol-enriched margarine spread contains 2 g of phytosterols, as determined by a specialized laboratory accredited by the China Food and Drug Administration. The regular and phytosterol-enriched margarine spreads were labeled with code to make the content blind to both the participants and investigators. Participants were instructed not to deviate from the suggested diets following their GDM diagnosis and especially not to consume any margarine spread other than those provided to them by the investigators during the study. Nutrient intakes of participants were analyzed using Nutritionist version 4 software (First Databank) modified for Chinese food. All the participants were visited at weekly intervals both to assess their compliance and to issue the margarine spread supply. Seven and nine participants from the placebo group and phytosterol group, respectively, withdrew from the study due to personal reasons or noncompliance to the study instructions. All measurements were conducted at week 0 (baseline) and week 16 (end of trial) by an investigator blind to the randomization assignments.

Metabolic profile assessment

Fasting blood samples (10 mL) were taken early morning after an overnight fast. Blood samples, collected into tubes containing 0.1% EDTA, were taken in a sitting position according to a standard protocol and centrifuged within 15 min of collection. The samples were centrifuged to separate the plasma, which were then stored at −70°C before analysis. Triacylglycerol (TAG), TC, LDL, and high-density lipoprotein (HDL) levels were quantified using commercial assay kits from BioVision according to the manufacturer's instructions. Plasma glucose levels were determined by glucometer (LifeScan SureStep) and plasma insulin levels were quantified by ELISA. Insulin resistance was assessed using the quantitative insulin check index (QUICKI) and homeostasis model of assessment of insulin resistance (HOMA-IR) and β-cell function (HOMA-B) as previously described.²⁰

Anthropometric measures

Body weight was measured in an overnight fasting status, using a digital scale to the nearest of 0.1 kg, while the participants were wearing light clothing and no shoes. Body height was measured with a stadiometer to the nearest of 0.1 cm. Body mass index (BMI) was calculated as weight in kg divided by height in m².

Statistical analyses

Values are shown as mean ± SD. Two-tailed Student's t-test was used to assess statistical differences between groups, and a P-value less than 0.05 was considered as statistically significant. All statistical analyses were performed using the SPSS software 18.0 (SPSS, Inc.).

Results

The study design of our trial is illustrated as a flow diagram in Figure 1. A total of 248 participants, who were diagnosed with GDM in their second trimester, were recruited for the study. Twenty-six of the initially recruited participants were excluded according to the exclusion criteria. The rest of the 222 eligible participants were then evenly assigned to the two margarine spread treatment groups, using a permuted-block randomization method stratified to their baseline 1 h OGTT results. All participants were instructed to consume two servings (10 g per serving) of either regular margarine spread as placebo or phytosterol-enriched margarine spread, with one serving at breakfast and another at dinner, on a daily basis for a period of 16 weeks. Of note, packages of the two kinds of spreads were coded to make their contents blind to both the participants and investigators. Participants were instructed not to consume any margarine spread other than those provided to them by the investigators during the study. All participants were visited on a weekly basis to assess their compliance to the study instructions. Seven participants in the placebo group and nine participants in the phytosterol group withdrew from the study, respectively, due to noncompliance and/or personal reasons. Eventually, a total of 104 participants in the placebo group and 102 participants in the phytosterol group have completed the trial, and their data were analyzed and listed in the current study.

FIG. 1.

Flow diagram of the study design.

In Table 1, we analyzed the general characteristics of participants in the two groups. We found no statistically significant differences in the age at pregnancy (29.2 ± 3.1 years vs. 29.4 ± 3.4 years, P = 0.53) and height (1.66 ± 0.08 m vs. 1.67 ± 0.09 m, P = 0.31) between participants from the two groups. Body weight of all participants was measured both at week 0 (baseline) and week 16 (end of trial), and it was not significantly different between the two groups either (week 0: 68.1 ± 7.2 kg vs. 68.6 ± 6.4 kg, P = 0.29; week 16: 72.5 ± 6.6 kg vs. 71.9 ± 7.1 kg, P = 0.36). We next calculated the BMI of all participants at week 0 and 16 and found that they were statistically similar as expected (week 0: 25.9 ± 4.2 vs. 26.2 ± 4.7, P = 0.47; week 16: 26.1 ± 3.8 vs. 26.5 ± 4.1, P = 0.33).

Table 1.

General Characteristics of Participants in the Two Treatment Groups

Characteristic	Placebo (n = 104)	Phytosterol (n = 102)	P
Age at pregnancy (years)	29.2 ± 3.1	29.4 ± 3.4	0.53
Height (m)	1.66 ± 0.08	1.67 ± 0.09	0.31
Body weight at week 0 (kg)	68.1 ± 7.2	68.6 ± 6.4	0.29
Body weight at week 16 (kg)	72.5 ± 6.6	71.9 ± 7.1	0.36
BMI at week 0 (kg/m²)	25.9 ± 4.2	26.2 ± 4.7	0.47
BMI at week 16 (kg/m²)	26.1 ± 3.8	26.5 ± 4.1	0.33

Values are mean ± SD.

BMI, body mass index.

Next, daily nutrient intakes throughout the study for all the participants were also analyzed (Table 2). There were no statistically significant differences between the two groups in daily dietary intakes, in terms of energy (2614 ± 190 kcal vs. 2581 ± 204 kcal, P = 0.45), proteins (102.3 ± 13.1 g vs. 98.7 ± 12.9 g, P = 0.34), fat (91.3 ± 12.6 g vs. 93.3 ± 13.1 g, P = 0.61), carbohydrates (326.5 ± 41.2 g vs. 337.1 ± 36.5 g, P = 0.52), as well as dietary (21.4 ± 3.7 g vs. 22.6 ± 4.8 g, P = 0.43) and soluble fibers (1.1 ± 0.4 g vs. 1.2 ± 0.3 g, P = 0.39).

Table 2.

Daily Nutrient Intakes of Participants Throughout the Study

Daily nutrient intakes	Placebo (n = 104)	Phytosterol (n = 102)	P
Energy (kcal)	2614 ± 190	2581 ± 204	0.45
Proteins (g)	102.3 ± 13.1	98.7 ± 12.9	0.34
Fat (g)	91.3 ± 12.6	93.3 ± 13.1	0.61
Carbohydrates (g)	326.5 ± 41.2	337.1 ± 36.5	0.52
Dietary fibers (g)	21.4 ± 3.7	22.6 ± 4.8	0.43
Soluble fibers (g)	1.1 ± 0.4	1.2 ± 0.3	0.39

Values are mean ± SD.

At week 0 and 16, we collected blood samples from participants of both groups and measured their lipid profile (Table 3). Over the 16-week treatment period, we observed significant decrease in the changes of TAG (+36.0 ± 61.7 mg/dL vs. −19.8 ± 55.6 mg/dL, P = 0.017), TC (+25.2 ± 41.6 mg/dL vs. −31.9 ± 48.3 mg/dL, P = 0.032), and LDL (+9.8 ± 19.2 mg/dL vs. −14.6 ± 25.9 mg/dL, P = 0.027), as well as significant increase in HDL (−6.6 ± 12.7 mg/dL vs. +5.9 ± 13.9 mg/dL, P = 0.041), by comparing these lipid profile parameters from week 0 to 16 between the placebo and phytosterol participants. Next, the ratio of TC/HDL was also calculated for all participants, and we found that the change over 16 weeks of treatment was significantly reduced (+0.1 ± 0.7 vs. −0.3 ± 0.6, P = 0.013) in the phytosterol treatment group. All the above lipid biomarker measurements indicated markedly improved lipid composition in the participants from the phytosterol group than those from the placebo group, which was consistent with previous report that phytosterol-enriched spread could lower TC and LDL levels among T2DM patients.¹⁸

Table 3.

Serum lipid Profile of Participants at Week 0 and 16

	Placebo (n = 104)			Phytosterol (n = 102)
Lipid profile	Week 0	Week 16	Change	Week 0	Week 16	Change	P
TAG (mg/dL)	183.4 ± 69.3	219.3 ± 72.2	+36.0 ± 61.7	192.1 ± 67.2	172.3 ± 58.3	−19.8 ± 55.6	0.017
TC (mg/dL)	211.6 ± 61.5	236.8 ± 59.2	+25.2 ± 41.6	217.2 ± 52.7	185.3 ± 56.4	−31.9 ± 48.3	0.032
LDL (mg/dL)	94.1 ± 25.2	103.9 ± 31.3	+9.8 ± 19.2	93.2 ± 27.3	78.6 ± 31.7	−14.6 ± 25.9	0.027
HDL (mg/dL)	73.1 ± 18.2	66.5 ± 19.6	−6.6 ± 12.7	74.2 ± 15.6	80.1 ± 13.2	+5.9 ± 13.9	0.041
TC/HDL ratio	3.1 ± 0.8	3.2 ± 1.0	+0.1 ± 0.7	3.0 ± 1.1	2.7 ± 0.9	−0.3 ± 0.6	0.013

Values are mean ± SD; P-values are intergroup comparison for changes in profile parameters between two groups.

HDL, high-density lipoprotein; LDL, low-density lipoprotein; TAG, triacylglycerol; TC, total cholesterol.

In addition, we also analyzed changes in their serum glucose metabolic profile from week 0 to 16. We found significant reductions in FPG level (−0.9 ± 4.8 mg/dL vs. −11.7 ± 6.8 mg/dL, P = 0.021), serum insulin level (+3.9 ± 4.9 μIU/mL vs. −2.1 ± 4.1 μIU/mL, P = 0.018), HOMA-IR (+0.8 ± 1.6 vs. −1.4 ± 1.3, P = 0.017), and HOMA-B scores (+19.1 ± 21.2 vs. −7.3 ± 19.8, P = 0.029), as well as significant increase in QUICKI score (−0.11 ± 0.05 vs. +0.03 ± 0.04, P = 0.35), by comparing the changes in these metabolic profile parameters from week 0 to 16 between the placebo and phytosterol participants (Table 4). These results demonstrated that 16 weeks of phytosterol-enriched margarine spread treatment markedly improved insulin resistance of GDM participants in the study.

Table 4.

Serum Glucose Metabolic Profile of Participants at Week 0 and 16

	Placebo (n = 104)			Phytosterol (n = 102)
Metabolic profile	Week 0	Week 16	Change	Week 0	Week 16	Change	P
FPG (mg/dL)	107.1 ± 3.9	106.2 ± 5.7	−0.9 ± 4.8	108.1 ± 7.3	96.4 ± 8.1	−11.7 ± 6.8	0.021
Insulin (μIU/mL)	12.0 ± 4.1	15.9 ± 6.3	+3.9 ± 4.9	12.3 ± 5.1	10.2 ± 4.6	−2.1 ± 4.1	0.018
HOMA-IR	3.0 ± 1.7	3.8 ± 2.1	+0.8 ± 1.6	2.9 ± 1.3	1.5 ± 1.6	−1.4 ± 1.3	0.017
HOMA-B	42.6 ± 23.5	61.7 ± 25.1	+19.1 ± 21.2	43.5 ± 21.7	36.2 ± 23.6	−7.3 ± 19.8	0.029
QUICKI	0.43 ± 0.05	0.32 ± 0.06	−0.11 ± 0.05	0.41 ± 0.06	0.44 ± 0.05	+0.03 ± 0.04	0.035

Values are mean ± SD; P-values are intergroup comparison for changes in profile parameters between two groups.

FPG, fasting plasma glucose; HOMA-IR, homeostasis model of assessment of insulin resistance; HOMA-B, homeostasis model of assessment of β cell function; QUICKI, quantitative insulin check index.

Discussion

GDM has become a concerning health problem among pregnant women throughout the world.² Dietary interventions have been reported to be beneficial in the clinical management of GDM symptoms.²¹ In the current randomized, placebo-controlled, and double-blind clinical trial, we have demonstrated that daily consumption of a phytosterol-enriched spread, for a period of 16 weeks during the second trimester of pregnancy, could markedly improve insulin resistance and lipid profile among GDM patients. To the best of our knowledge, our current clinical study is the first to evaluate the effects of phytosterol-enriched spread on glucose and insulin metabolism and lipid profile in women diagnosed with GDM.

Symptoms such as insulin resistance and glucose intolerance, also seen in T2DM patients, are frequent among GDM-affected women. However, unlike many T2DM patients, GDM patients face less clinical treatment options, since lots of drugs proved useful in managing T2DM symptoms are not suitable for pregnant women, and therefore, dietary intervention might be the only safe approach in the management of GDM. Dietary intervention therapies have yielded promising results, for instance, vitamin D supplementation has been reported to alleviate insulin resistance in T2DM.²² Therapies that were shown to alleviate diabetic symptoms in T2DM could potentially be applied to the clinical management of GDM, hopefully with higher chance of success. Of particular interest to our current study, in a clinical trial among T2DM patients, Lee et al. found that a phytosterol-enriched spread was effective in lowering TC and LDL levels.¹⁸ The effect was significant at the beginning but became mild and wore off after a period of 8–12 weeks. This was likely due to the free-living conditions the trial by Lee et al. was conducted, in which nutrient intakes of participants were not monitored at all.

In light of the study by Lee et al., we designed our current trial, aiming to investigate if the alleviating effect of phytosterol-enriched spreads on lowering TC and LDL could also be applied to GDM patients. Indeed, after 16 weeks of consuming margarine spreads enriched in phytosterols, lipid composition of GDM patients was greatly improved, as evidenced by decreased levels of TAG, TC, and LDL, as well as increased HDL. These data are highly consistent with results from Lee et al., which by itself supported a plausible adaptation of applying therapies effective on T2DM on GDM, both of which exhibit common symptoms. More importantly, we found that insulin and glucose metabolism of GDM patients were also greatly improved, in terms of FPG and insulin levels, as well as HOMA-IR, HOMA-B, and QUICKI scores, all of which are important diagnostic factors. These results together clearly indicated significant attenuation of insulin resistance.

Several factors may explain these remarkable results observed in our current trial. First of all, in selecting participants, unlike in the report of Lee et al., we excluded all participants who consumed margarine or butter during the 6 months before being recruited into the study. Moreover, we made it a compliance requirement that participants were not to consume any margarine spread other than those provided to them, and several participants were withdrawn from the study due to this reason. Owing to these above strict criteria and the fact that margarine spread is not habitually used in Chinese food, we managed to maintain relatively free-living conditions in a large sample pool of participants. In addition, we have also recorded daily nutrient intakes of all participants, which have made it more reliable to compare their metabolic profiles based on similar nutrient intakes without potential disturbance of different food sources.

To conclude, our present randomized, placebo-controlled double-blind clinical trial, conducted under relatively free-living conditions, is the first to demonstrate that daily consumption of a phytosterol-enriched spread has improved lipid profile and insulin resistance in pregnant GDM women.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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