楊雅 趙梅
摘 要:妊娠期糖尿病(GDM)是妊娠期常見的一種并發癥。由于妊娠孕婦所處階段特殊性,強調防治措施首先以調整飲食為主。GDM孕婦在發病機理方面存在著胰島素抵抗和胰腺β細胞凋亡現象,脂肪酸誘導胰島素抵抗在GDM發生發展中作用目前仍存在一定爭議。本文綜述膳食飽和脂肪酸、多不飽和脂肪酸、單不飽和脂肪酸及反式脂肪酸與GDM關系的研究進展,為GDM孕婦攝入合理膳食脂肪酸提供科學依據。
關鍵詞:妊娠期糖尿病;飽和脂肪酸;多不飽和脂肪酸;單不飽和脂肪酸;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異常或者糖尿病,而在妊娠期24~28周口服75g葡萄糖耐量試驗后確診存在糖耐量異常,是妊娠期并發癥的一種常見類型[1]。國際糖尿病聯合會 (IDF)公布的2017年全球20~49歲妊娠婦女GDM發病率為14%,參考國際糖尿病流行病學,約16.8%的孕婦妊娠期間處于高血糖狀態,其中84%后期被診斷為GDM[2]。美國糖尿病協會(ADA)在2014年糖尿病診斷標準中提及的GDM患病率也高達15%~20%,且呈逐漸上升趨勢[3]。Christian M等[4]通過前瞻性研究表明,近10年來澳大利亞GDM發病率提高近10%,黃種人發病率顯著高于其他種族發病率,約為其他種族的3~7倍,且該研究也發現,亞洲黃種人孕婦出現GDM風險顯著高于其他種族。我國曾在2010—2011年按照國際妊娠合并糖尿病研究協會對國內13家醫院孕婦的調查報告顯示,我國GDM發病率為17.5%[5],也有一項Meta分析顯示,中國大陸GDM發病率在5.12%~33.3%之間[6]。GDM會帶來嚴重不良影響[7],孕婦容易發生妊娠期高血壓病、羊水過多、胎膜早破、感染、早產等并發癥,嚴重時可導致酮癥酸中毒;胎兒容易發生自然流產、畸形和缺氧,有時會發生宮內死亡,高血糖易引起胎兒巨大,導致分娩時出現難產幾率增加,新生兒出現新生兒呼吸窘迫綜合征、低血糖和其他并發癥幾率增加,包括嚴重情況下死亡。
GDM發生與家族遺傳、不良生活方式和飲食習慣等因素密切相關。膳食攝入作為可控改變因素,是預防及治療GDM首選且安全的措施,約80%~90%的患者經膳食控制可降低血糖水平,利于患者預后。膳食脂肪酸作為人體主要能量來源,攝入及代謝不平衡導致多種疾病發生,膳食脂肪酸與GDM關系成為臨床學科及營養學科關注的重點。脂肪酸在葡萄糖代謝環節發揮重要調節作用,正常妊娠時由于體內激素水平變化引起脂肪動員分解加速,造成生理性胰島素抵抗發生,當攝入膳食脂肪酸過多時,導致胰島素抵抗增強,增加GDM發病風險;大量流行病學、臨床和動物實驗發現,膳食脂肪酸種類及構成對GDM有重要影響。脂肪酸是最簡單的一種脂質,是脂肪和類脂的物質基礎,通過影響細胞膜磷脂組成來改變細胞功能,從而增加GDM發病風險[8]。脂肪酸根據碳氫鍵數目和飽和程度分為飽和脂肪酸(SFA)、單不飽和脂肪酸(MUFA)和多不飽和脂肪酸(PUFA)。
1 SFA與GDM
SFA有36種亞型,其中棕櫚酸(PA)及硬脂酸(SA)是常見類型,可導致胰島素抵抗[9]。大部分研究者認為,食用高脂肪食物,在一定程度上可增加GDM發病風險。有研究對糖尿病組與正常組進行飲食調查,得出高SFA攝入量可提高糖尿病發病率[10]。李青青等[11]通過對PA與胰島素抵抗指數相關性進行多元回歸分析發現,SFA尤其是PA在一定程度上刺激胰島素分泌,機體長期保持高水平胰島素可致使β細胞毒性和功能衰竭,促使機體胰島素敏感性降低。Zhu Y等[12]將膳食SFA分為偶數鏈和奇數鏈SFA,發現越高濃度偶數鏈SFA和越低濃度奇數鏈SFA協同增加GDM發病風險。Harris等[13]認為,患有2型糖尿病個體在紅細胞膜中具有較高水平PA。Cinelli G等[14]發現,妊娠28~34周GDM女性紅細胞膜中SFA比例尤其是PA含量較高。Palomer等[15]研究表明,PA通過三種機制介導炎癥和胰島素抵抗,從而導致糖尿病發生:(1)導致有害復合脂質增加,如二酰基甘油;(2)導致細胞功能受損,過量PA損害內質網及線粒體的功能;(3)通過胎球蛋白A激活Toll4樣受體,高脂飲食會增加脂多糖水平,脂多糖是Toll4受體活化劑,Toll4受體激活促炎途徑。
2 MUFA與GDM
油酸(OA)是MUFA中最有代表性的順式脂肪酸,是橄欖油的一種主要成分,橄欖油是地中海飲食中膳食脂肪的主要來源[16]。Bowen KJ等[17]研究發現,MUFA和機體血脂高低水平呈正相關,高水平MUFA通過降低膽固醇氧化敏感性來降低低密度脂蛋白,降低血液粘稠度減少凝集而保護機體血管內皮。也有研究發現,MUFA在血糖控制上具有一定影響,通過增加膳食中MUFA,可以降低2型糖尿病病人血糖[18]。屈家滿等[19]通過隨機對照實驗,常規組給予常規膳食,MUFA組在此基礎上膳食調整MUFA,干預后MUFA組FBG、2hPBG、HbAlc、TG、TC、LDL明顯低于常規組,HDL明顯高于常規組,表明MUFA能有效改善患者糖脂代謝紊亂狀態。Qian等[20]通過RCT薈萃分析發現,與高碳水化合物及高PUFA膳食相比,高MUFA飲食后空腹血糖水平降低更顯著。也有研究指出,用MUFA代替碳水化合物飲食,通過血糖負荷降低、胰島素分泌連續性減少及胰島素敏感性增加得出MUFA對血糖控制具有積極作用[21]。
3 PUFA與GDM
PUFA指分子結構中含有2個或2個以上雙鍵。研究顯示,PUFA對GDM保護機制可能是膳食PUFA不僅能增加脂肪細胞內膜脂肪細胞葡萄糖轉載體 (GLUT),還可以將GLUT從細胞內膜轉移到細胞外膜,有利于葡萄糖從細胞外轉運到細胞內,促進胰島素發揮作用,降低GDM發病風險[22]。有研究將正常孕婦和GDM孕婦對比發現,GDM孕婦胰島素及胰島素抵抗指數均顯著高于正常孕婦,且研究證明,同種類型PUFA低劑量時可改善孕婦體內脂肪分布及代謝,而高劑量PUFA在一定程度上可降低胰島素敏感性[23]。顧雅娟等[24]對孕婦血清檢測發現,正常孕婦血清PUFA水平比GDM孕婦高,且兩組研究對象中胰島素抵抗指數與血清PUFA呈負相關。動物模型[25]也證明,攝入PUFA能顯著改善GDM胰島素抵抗作用。PUFA可分為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轉歸上發揮著更重要作用[26-28]。
3.1 ω-3 PUFA與GDM
ω-3 PUFA主要包括α-亞麻酸(ALA)、二十碳五烯酸(EPA)、二十二碳六烯酸(DHA),EPA和DHA在體內不能合成,必須由食物供給,稱為必需脂肪酸,海洋生物或深海魚類,如沙丁魚、鮭魚、青魚等是ω-3 PUFA的主要來源。研究發現,愛斯基摩人中GDM發病率比較低,因愛斯基摩人食用海洋魚類,魚類富含ω-3 PUFA,因此食用富含ω-3 PUFA深海魚及其他海產品發生糖尿病危險性明顯降低[29]。Wang J等[30]通過系統評價和薈萃分析發現,ω-3 PUFA改善胰島素敏感性,降低糖尿病發病風險原因可能為:(1)ω-3 PUFA有助于維持免疫防御系統,促進T輔助(Th)細胞分化為Th2表型,改變Th1 / Th2比例來保護抗炎Th2表型;(2)ω-3 PUFA抑制促炎細胞因子和核NF-κB蛋白表達;(3)EPA攝入可抑制促炎介質,導致脂聯素等抗炎分子增加,從而逆轉胰島素抵抗。也有研究指出,ω-3 PUFA對糖尿病人的空腹血糖、胰島素抵抗及糖化血紅蛋白沒有影響[31-32]。
3.2 ω-6 PUFA與GDM
ω-6 PUFA主要包括亞油酸(LA)、γ亞麻酸、花生四烯酸(AA),植物油是ω-6 PUFA的主要來源。ω-6 PUFA同樣具有增強免疫能力、改善脂質代謝、預防動脈硬化、降低血糖的作用[33]。Harris等[13]發現,血漿和紅細胞膜中ω-6 PUFA與2型糖尿病發病率呈負相關。Forouhi N G等[34]發現,增加ω-6 PUFA 攝入降低糖尿病發病率。MMarina F等[35]研究發現,與血糖正常孕婦相比,GDM孕婦血清和血漿中總ω-6 PUFA和花生四烯酸水平沒有差異,但在GDM孕婦分娩后7~12個月,血清中總ω-6 PUFA水平升高。
3.3 ω-6/ω-3 PUFA比例與GDM
目前有關ω-6/ω-3 PUFA比例與GDM作用機制還沒有定論,現有解釋為 LA和ALA在體內是合成ω-6 PUFA和ω-3 PUFA的前體,二者在體內共用同一合成通路,ω-6 PUFA和ω-3 PUFA競爭去飽和酶和碳鏈延長酶,通過去飽和和延長作用,將LA轉變為AA,ALA轉變為EPA和DHA,膳食中一方攝入增加會導致另一方在體內合成PUFA含量減少[36]。一項普通人群干預研究發現,食用ω-3 PUFA含量較高魚油組,比食用ω-6 PUFA含量較高紅花油組更能改善機體胰島素抵抗狀態[37]。ω-3 PUFA和ω-6 PUFA之間不能相互轉化,攝入PUFA只有在數量及比例上合理,才能充分發揮保護性作用。Tracey J Brown等[38]通過對長鏈PUFA與GDM關系進行系統評價和Meta分析得出,沒有證據直接表明ω-6/ω-3 PUFA比例對GDM或葡萄糖代謝起重要作用。
4 反式脂肪酸與GDM
膳食中含有兩種不同來源反式脂肪酸(TFA):氫化植物油中工業TFA和反芻動物TFA,包括共軛亞油酸(CLA)。Salmerón J等[39]通過14年前瞻性研究發現,用PUFA代替等能量TFA時,2型糖尿病患病率降低,說明TFA是糖尿病的獨立危險因素。Liu B等[40]調查血漿中4種主要TFA異構體(反油酸、棕櫚反油酸、異油酸、亞油酸)濃度與糖尿病之間關系,尤其是反油酸,即使在控制其他危險因素后,在成年人中仍與糖尿病呈正相關。總TFAs、反油酸、棕櫚反油酸和異油酸與無糖尿病成年人葡萄糖代謝變化生物標志物呈正相關,也有研究報告顯示,反式棕櫚酸和反油酸都與糖尿病沒有顯著關聯[41]。有研究指出,反芻動物血漿TFA 水平與2型糖尿病呈負相關[42],一項在血糖正常孕婦研究報告指出,工業TFA與血漿F2-異丙基水平升高有關[43],這是氧化應激標志,而反芻動物TFA 則沒有相關性,說明工業和反芻動物TFA可能影響不同代謝結局。已有研究指出,即使很小劑量的工業TFA對人體造成的傷害要比反芻動物TFA嚴重的多[44],可導致血脂代謝紊亂,膳食中TFA含量增多是胰島素抵抗、糖尿病的危險因素。
5 結論
目前,對于GDM孕婦沒有特定膳食脂肪酸推薦攝入量,懷孕期間膳食脂肪酸建議與一般人群推薦相似。世界衛生組織建議[45]:總脂肪供給熱能應占總熱能<30 %,其中SFA供給熱能<10 %、PUFA供給熱能<10 %、MUFA供給熱能<10 %~15 %、TFA供給熱能<1%。適當增加UFA攝入,減少SFA攝入,使得SFA、MUFA及PUFA各占比重接近1/3、1/3、1/3,能夠有效緩解GDM患者血糖升高,為孕婦飲食指導和治療提供科學依據。◇
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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)