膳食脂肪酸与妊娠期糖尿病关系的研究进展
2020-09-10杨雅赵梅
杨雅 赵梅
摘 要:妊娠期糖尿病(GDM)是妊娠期常见的一种并发症。由于妊娠孕妇所处阶段特殊性,强调防治措施首先以调整饮食为主。GDM孕妇在发病机理方面存在着胰岛素抵抗和胰腺β细胞凋亡现象,脂肪酸诱导胰岛素抵抗在GDM发生发展中作用目前仍存在一定争议。本文综述膳食饱和脂肪酸、多不饱和脂肪酸、单不饱和脂肪酸及反式脂肪酸与GDM关系的研究进展,为GDM孕妇摄入合理膳食脂肪酸提供科学依据。
关键词:妊娠期糖尿病;饱和脂肪酸;多不饱和脂肪酸;单不饱和脂肪酸;反式脂肪酸
妊娠期糖尿病(gestational diabetes mellitus,GDM)是指妊娠前不存在糖耐量异常或者糖尿病,而在妊娠期24~28周口服75g葡萄糖耐量试验后确诊存在糖耐量异常,是妊娠期并发症的一种常见类型[1]。国际糖尿病联合会 (IDF)公布的2017年全球20~49岁妊娠妇女GDM发病率为14%,参考国际糖尿病流行病学,约16.8%的孕妇妊娠期间处于高血糖状态,其中84%后期被诊断为GDM[2]。美国糖尿病协会(ADA)在2014年糖尿病诊断标准中提及的GDM患病率也高达15%~20%,且呈逐渐上升趋势[3]。Christian M等[4]通过前瞻性研究表明,近10年来澳大利亚GDM发病率提高近10%,黄种人发病率显著高于其他种族发病率,约为其他种族的3~7倍,且该研究也发现,亚洲黄种人孕妇出现GDM风险显著高于其他种族。我国曾在2010—2011年按照国际妊娠合并糖尿病研究协会对国内13家医院孕妇的调查报告显示,我国GDM发病率为17.5%[5],也有一项Meta分析显示,中国大陆GDM发病率在5.12%~33.3%之间[6]。GDM会带来严重不良影响[7],孕妇容易发生妊娠期高血压病、羊水过多、胎膜早破、感染、早产等并发症,严重时可导致酮症酸中毒;胎儿容易发生自然流产、畸形和缺氧,有时会发生宫内死亡,高血糖易引起胎儿巨大,导致分娩时出现难产几率增加,新生儿出现新生儿呼吸窘迫综合征、低血糖和其他并发症几率增加,包括严重情况下死亡。
GDM发生与家族遗传、不良生活方式和饮食习惯等因素密切相关。膳食摄入作为可控改变因素,是预防及治疗GDM首选且安全的措施,约80%~90%的患者经膳食控制可降低血糖水平,利于患者预后。膳食脂肪酸作为人体主要能量来源,摄入及代谢不平衡导致多种疾病发生,膳食脂肪酸与GDM关系成为临床学科及营养学科关注的重点。脂肪酸在葡萄糖代谢环节发挥重要调节作用,正常妊娠时由于体内激素水平变化引起脂肪动员分解加速,造成生理性胰岛素抵抗发生,当摄入膳食脂肪酸过多时,导致胰岛素抵抗增强,增加GDM发病风险;大量流行病学、临床和动物实验发现,膳食脂肪酸种类及构成对GDM有重要影响。脂肪酸是最简单的一种脂质,是脂肪和类脂的物质基础,通过影响细胞膜磷脂组成来改变细胞功能,从而增加GDM发病风险[8]。脂肪酸根据碳氢键数目和饱和程度分为饱和脂肪酸(SFA)、单不饱和脂肪酸(MUFA)和多不饱和脂肪酸(PUFA)。
1 SFA与GDM
SFA有36种亚型,其中棕榈酸(PA)及硬脂酸(SA)是常见类型,可导致胰岛素抵抗[9]。大部分研究者认为,食用高脂肪食物,在一定程度上可增加GDM发病风险。有研究对糖尿病组与正常组进行饮食调查,得出高SFA摄入量可提高糖尿病发病率[10]。李青青等[11]通过对PA与胰岛素抵抗指数相关性进行多元回归分析发现,SFA尤其是PA在一定程度上刺激胰岛素分泌,机体长期保持高水平胰岛素可致使β细胞毒性和功能衰竭,促使机体胰岛素敏感性降低。Zhu Y等[12]将膳食SFA分为偶数链和奇数链SFA,发现越高浓度偶数链SFA和越低浓度奇数链SFA协同增加GDM发病风险。Harris等[13]认为,患有2型糖尿病个体在红细胞膜中具有较高水平PA。Cinelli G等[14]发现,妊娠28~34周GDM女性红细胞膜中SFA比例尤其是PA含量较高。Palomer等[15]研究表明,PA通过三种机制介导炎症和胰岛素抵抗,从而导致糖尿病发生:(1)导致有害复合脂质增加,如二酰基甘油;(2)导致细胞功能受损,过量PA损害内质网及线粒体的功能;(3)通过胎球蛋白A激活Toll4样受体,高脂饮食会增加脂多糖水平,脂多糖是Toll4受体活化剂,Toll4受体激活促炎途径。
2 MUFA与GDM
油酸(OA)是MUFA中最有代表性的顺式脂肪酸,是橄榄油的一种主要成分,橄榄油是地中海饮食中膳食脂肪的主要来源[16]。Bowen KJ等[17]研究发现,MUFA和机体血脂高低水平呈正相关,高水平MUFA通过降低胆固醇氧化敏感性来降低低密度脂蛋白,降低血液粘稠度减少凝集而保护机体血管内皮。也有研究发现,MUFA在血糖控制上具有一定影响,通过增加膳食中MUFA,可以降低2型糖尿病病人血糖[18]。屈家满等[19]通过随机对照实验,常规组给予常规膳食,MUFA组在此基础上膳食调整MUFA,干预后MUFA组FBG、2hPBG、HbAlc、TG、TC、LDL明显低于常规组,HDL明显高于常规组,表明MUFA能有效改善患者糖脂代谢紊乱状态。Qian等[20]通过RCT荟萃分析发现,与高碳水化合物及高PUFA膳食相比,高MUFA饮食后空腹血糖水平降低更显著。也有研究指出,用MUFA代替碳水化合物饮食,通过血糖负荷降低、胰岛素分泌连续性减少及胰岛素敏感性增加得出MUFA对血糖控制具有积极作用[21]。
3 PUFA與GDM
PUFA指分子结构中含有2个或2个以上双键。研究显示,PUFA对GDM保护机制可能是膳食PUFA不仅能增加脂肪细胞内膜脂肪细胞葡萄糖转载体 (GLUT),还可以将GLUT从细胞内膜转移到细胞外膜,有利于葡萄糖从细胞外转运到细胞内,促进胰岛素发挥作用,降低GDM发病风险[22]。有研究将正常孕妇和GDM孕妇对比发现,GDM孕妇胰岛素及胰岛素抵抗指数均显著高于正常孕妇,且研究证明,同种类型PUFA低剂量时可改善孕妇体内脂肪分布及代谢,而高剂量PUFA在一定程度上可降低胰岛素敏感性[23]。顾雅娟等[24]对孕妇血清检测发现,正常孕妇血清PUFA水平比GDM孕妇高,且两组研究对象中胰岛素抵抗指数与血清PUFA呈负相关。动物模型[25]也证明,摄入PUFA能显著改善GDM胰岛素抵抗作用。PUFA可分为ω-3族、ω-6族、ω-7族、ω-9族,其中ω-3族和ω-6族在病理生理和疾病转归上发挥着更重要作用[26-28]。
3.1 ω-3 PUFA与GDM
ω-3 PUFA主要包括α-亚麻酸(ALA)、二十碳五烯酸(EPA)、二十二碳六烯酸(DHA),EPA和DHA在体内不能合成,必须由食物供给,称为必需脂肪酸,海洋生物或深海鱼类,如沙丁鱼、鲑鱼、青鱼等是ω-3 PUFA的主要来源。研究发现,爱斯基摩人中GDM发病率比较低,因爱斯基摩人食用海洋鱼类,鱼类富含ω-3 PUFA,因此食用富含ω-3 PUFA深海鱼及其他海产品发生糖尿病危险性明显降低[29]。Wang J等[30]通过系统评价和荟萃分析发现,ω-3 PUFA改善胰岛素敏感性,降低糖尿病发病风险原因可能为:(1)ω-3 PUFA有助于维持免疫防御系统,促进T辅助(Th)细胞分化为Th2表型,改变Th1 / Th2比例来保护抗炎Th2表型;(2)ω-3 PUFA抑制促炎细胞因子和核NF-κB蛋白表达;(3)EPA摄入可抑制促炎介质,导致脂联素等抗炎分子增加,从而逆转胰岛素抵抗。也有研究指出,ω-3 PUFA对糖尿病人的空腹血糖、胰岛素抵抗及糖化血红蛋白没有影响[31-32]。
3.2 ω-6 PUFA与GDM
ω-6 PUFA主要包括亚油酸(LA)、γ亚麻酸、花生四烯酸(AA),植物油是ω-6 PUFA的主要来源。ω-6 PUFA同样具有增强免疫能力、改善脂质代谢、预防动脉硬化、降低血糖的作用[33]。Harris等[13]发现,血浆和红细胞膜中ω-6 PUFA与2型糖尿病发病率呈负相关。Forouhi N G等[34]发现,增加ω-6 PUFA 摄入降低糖尿病发病率。MMarina F等[35]研究发现,与血糖正常孕妇相比,GDM孕妇血清和血浆中总ω-6 PUFA和花生四烯酸水平没有差异,但在GDM孕妇分娩后7~12个月,血清中总ω-6 PUFA水平升高。
3.3 ω-6/ω-3 PUFA比例与GDM
目前有关ω-6/ω-3 PUFA比例与GDM作用机制还没有定论,现有解释为 LA和ALA在体内是合成ω-6 PUFA和ω-3 PUFA的前体,二者在体内共用同一合成通路,ω-6 PUFA和ω-3 PUFA竞争去饱和酶和碳链延长酶,通过去饱和和延长作用,将LA转变为AA,ALA转变为EPA和DHA,膳食中一方摄入增加会导致另一方在体内合成PUFA含量减少[36]。一项普通人群干预研究发现,食用ω-3 PUFA含量较高鱼油组,比食用ω-6 PUFA含量较高红花油组更能改善机体胰岛素抵抗状态[37]。ω-3 PUFA和ω-6 PUFA之间不能相互转化,摄入PUFA只有在数量及比例上合理,才能充分发挥保护性作用。Tracey J Brown等[38]通过对长链PUFA与GDM关系进行系统评价和Meta分析得出,没有证据直接表明ω-6/ω-3 PUFA比例对GDM或葡萄糖代谢起重要作用。
4 反式脂肪酸与GDM
膳食中含有两种不同来源反式脂肪酸(TFA):氢化植物油中工业TFA和反刍动物TFA,包括共轭亚油酸(CLA)。Salmerón J等[39]通过14年前瞻性研究发现,用PUFA代替等能量TFA时,2型糖尿病患病率降低,说明TFA是糖尿病的独立危险因素。Liu B等[40]调查血浆中4种主要TFA异构体(反油酸、棕榈反油酸、异油酸、亚油酸)浓度与糖尿病之间關系,尤其是反油酸,即使在控制其他危险因素后,在成年人中仍与糖尿病呈正相关。总TFAs、反油酸、棕榈反油酸和异油酸与无糖尿病成年人葡萄糖代谢变化生物标志物呈正相关,也有研究报告显示,反式棕榈酸和反油酸都与糖尿病没有显著关联[41]。有研究指出,反刍动物血浆TFA 水平与2型糖尿病呈负相关[42],一项在血糖正常孕妇研究报告指出,工业TFA与血浆F2-异丙基水平升高有关[43],这是氧化应激标志,而反刍动物TFA 则没有相关性,说明工业和反刍动物TFA可能影响不同代谢结局。已有研究指出,即使很小剂量的工业TFA对人体造成的伤害要比反刍动物TFA严重的多[44],可导致血脂代谢紊乱,膳食中TFA含量增多是胰岛素抵抗、糖尿病的危险因素。
5 结论
目前,对于GDM孕妇没有特定膳食脂肪酸推荐摄入量,怀孕期间膳食脂肪酸建议与一般人群推荐相似。世界卫生组织建议[45]:总脂肪供给热能应占总热能<30 %,其中SFA供给热能<10 %、PUFA供给热能<10 %、MUFA供给热能<10 %~15 %、TFA供给热能<1%。适当增加UFA摄入,减少SFA摄入,使得SFA、MUFA及PUFA各占比重接近1/3、1/3、1/3,能够有效缓解GDM患者血糖升高,为孕妇饮食指导和治疗提供科学依据。◇
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Abstract:The gestational diabetes mellitus (GDM)is a common complication of pregnancy.Because of the particularity of pregnancy patients,the prevention and treatment measures are mainly to adjust diet.The pathogenesis of GDM is insulin resistance and pancreatic beta cell apoptosis.The role of fatty acid induced insulin resistance in the development of GDM remains controversial.The relationship between saturated fatty acids,polyunsaturated fatty acids,monounsaturated fatty acids and trans fatty acids and GDM was discussed to provide scientific evidence for GDM patients to absorb reasonable dietary fat.
Keywords:gestational diabetes mellitus (GDM);saturated fatty acid(SFA);polyunsaturated fatty acid(PUFA);monounsaturated fatty acid(MUFA);trans fatty acid(TFA)