n-3多不饱和脂肪酸分类、来源与疾病防治功能

n-3多不饱和脂肪酸包括ALA、EPA、DPA和DHA等。增加n-3多不饱和脂肪酸摄取量可以促进婴幼儿视网膜、大脑和神经系统发育；n-3多不饱和脂肪酸通过各种途径降低人体心血管疾病和炎症的发生，降低糖尿病患者血清LDL-C和TG水平，抑制体外培养的乳腺、前列腺和结肠癌细胞增生，促进细胞凋亡。     

n-3多不饱和脂肪酸与2型糖尿病关系的研究进展

综述了n-3多不饱和脂肪酸是否可以减少或延缓健康人群发生糖尿病及其血管并发症的风险,以及2型糖尿病患者中外源性n-3多不饱和脂肪酸的摄入是否可以改善胰岛素抵抗和降低心血管疾病并发症的发生发展的临床研究进展,从而探索其在医学营养治疗学中的应用价值。     

膳食中n-3多不饱和脂肪酸对2型糖尿病患者血糖和胰岛素敏感性的影响

2型糖尿病是世界上最常见的慢性疾病之一。膳食中的n-3多不饱和脂肪酸可能会减少亚洲人的2型糖尿病风险, 中国2型糖尿病患者血浆磷脂n-3不饱和脂肪酸与胰岛素敏感性呈正相关。而欧美的前瞻性研究均发现, 鱼类的摄入和n-3多不饱和脂肪酸的摄入会增加2型糖尿病的发病风险, 在西方白种人群中进行的n-3多不饱和脂肪酸干预的随机对照试验也并未发现n-3多不饱和脂肪酸能够改善患者胰岛素抵抗水平或血糖水平, n-3多不饱和脂肪酸甚至可轻微地降低患者胰岛素的敏感性。本文综述了目前n-3多不饱和脂肪酸摄入量与2型糖尿病风险之间的关系。     

n-3/n-6多不饱和脂肪酸的生理功能与膳食平衡研究

多不饱和脂肪酸(PUFAs)是一种独特的生物活性物质,对人体有着重要的生理功能。其中,n-3/n-6多不饱和脂肪酸具有重要的生物学功能,它们在人体内的平衡对于维持细胞的正常生理功能、促进血清胆固醇的代谢、降低血液黏稠度以及增强记忆、活跃思维等方面起着重要作用。综述n-3/n-6多不饱和脂肪酸的生理功能及膳食平衡等研究进展,为后续研究提供理论依据。     

不同类型n-3多不饱和脂肪酸对心血管疾病的防治作用及其机制研究进展

3种主要的食源性n-3多不饱和脂肪酸包括α-亚麻酸(ALA)、二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)。综述了ALA、EPA和DHA降低甘油三酸酯水平和血小板凝集,改善炎症和氧化应激指标以及改善血管和心脏血液动力学的功能,从而对动脉粥样硬化等心血管疾病起到防治作用。此外,总结了联合使用ALA、EPA和DHA防治心血管疾病的作用,并进行了展望。     

n-6/n-3多不饱和脂肪酸比例对HepG2细胞脂代谢的影响

本文研究了不同比例n-6/n-3多不饱和脂肪酸对HepG2细胞影响,通过体外培养细胞60μM不同比例LA/ALA培养24 h,通过反转录PCR研究不同比例LA/ALA对HepG2细胞SREBP-1、FAS、HMG-CR、LDLr和Apo B蛋白等脂代谢相关基因及蛋白表达量的影响。结果表明在组1(LA)、组2(10:1 LA/ALA)、组3(5:1 LA/ALA)、组4(1:1 LA/ALA)、组5(1:5 LA/ALA)、组6(1:10LA/ALA)和组7(ALA)7组比例中,1:1 LA/ALA比例处理细胞效果最佳,此比例脂肪酸通过下调HepG2细胞SREBP-1和FAS基因的表达来降低细胞TG的含量;下调HMG-CR基因的表达,上调LDLr基因的表达来降低细胞TC和LDL-C含量;通过上调SR-B1基因表达增加胆固醇逆转运,从而实现对HepG2脂代谢的有效调控。此多不饱和脂肪酸体外营养评价模型,为n-6/n-3多不饱和脂肪酸最佳营养比例推荐及食用植物油中多不饱和脂肪酸比例营养评估提供理论依据。     

n-3多不饱和脂肪酸对中老年人群精神及视力影响的研究进展

通过综述n-3多不饱和脂肪酸对中老年人群疾病,特别是对中老年人群认知下降、老年痴呆、抑郁、黄斑变性等作用的研究,阐述了n-3多不饱和脂肪酸对认知下降风险的降低,以及对AMD病症发生的减缓作用。同时,n-3多不饱和脂肪酸在细胞中的含量与抑郁症发病率呈负相关性。尽管确切机理有待深入研究,但绝大部分临床研究表明,补充n-3多不饱和脂肪酸可以预防中老年人群精神及视力疾病的发生。     

N3系多不饱和脂肪酸膳食参考摄入量的研究进展

近年来n-3系多不饱和脂肪酸(N-3 Polyunsaturated Fatty Acids,n-3 PUFAs)在提高婴幼儿认知及视力发育、增强免疫及预防精神疾病、癌症、炎症、心血管疾病(Cardiovascular Disease,CVD)等方面的作用倍受人们的重视,n-3PUFAs的膳食参考摄入量也成为这些研究领域的重要关注焦点之一。为了更好地发挥n-3 PUFAs在促进人体营养、发育、健康以及疾病预防等方面的重要作用,本文综述了世界上许多知名的研究机构及官方组织关于对不同人群的n-3 PUFAs推荐摄入量(Recommended Nutrient Intake,RNI)及适宜摄入量(Adequate Intake,AI),以及它们对n-6/n-3脂肪酸的摄入比例以及n-3 PUFAs的可耐受最高摄入量(Tolerable Upper Intake Level,UL)进行的科学研究、探讨,同时还对n-3 PUFAs在使用过程中的不稳定性及注意事项进行了阐述,可以为我国不同人群的n-3 PUFAs膳食参考摄入量、普通食品中应用添加n-3 PUFAs以及n-3 PUFAs摄入补充方面提供更加充分、完整的科学依据和参考。     

反式脂肪酸与Ⅱ型糖尿病、心血管疾病的关系及作用机制

依据目前国内外有关反式脂肪酸TFA(trans fatty acids)的流行病学研究成果和一些相关研究报告指出,TFA与人类Ⅱ型糖尿病、心血管疾病有相关性.TFA对人体的病理效应在于,它对血脂、炎症因子、内皮细胞功能、胰岛素抵抗及免疫力等有重要影响.膳食中的TFA进入机体组织器官后,将与多不饱和脂肪酸竞争结合过氧化物酶体增殖物活化受体PPARs(peroxisome proliferation activatedreceptors),下调PPARs对机体的保护作用,降低脂肪酸代谢酶、细胞葡萄糖转运体基因的表达,降低胰岛素受体的敏感性,并增强炎症因子的表达,造成血脂异常,胰岛素抵抗,血管内皮重构,功能紊乱,进而诱发Ⅱ型糖尿病、心血管疾病.     

n-3多不饱和脂肪酸抑制骨骼肌蛋白异常分解的研究进展

胰岛素/Akt信号通路受阻所致的骨骼肌细胞蛋白异常分解,可能是骨骼肌萎缩发生的重要原因。不同n-3多不饱和脂肪酸在骨骼肌细胞内、外作用于胰岛素/Akt信号通路上的多个位点,均有助于维持通路的正常运作。其中,植物来源n-3多不饱和脂肪酸ALA能通过活化胰岛β细胞胞膜的GPR40直接促进胰岛素分泌;海鱼来源n-3多不饱和脂肪酸EPA与DHA能有效维持骨骼肌细胞内Akt活性并增加胰岛素敏感性。本文通过对相关文献的归纳总结,阐释n-3多不饱和脂肪酸基于胰岛素/Akt信号通路抑制骨骼肌细胞蛋白异常分解的机制,为通过膳食手段干预骨骼肌萎缩提供新的思路。     

鱼油补充对中老年人群炎性衰老及相关疾病有益作用的研究进展

鱼油富含n-3多不饱和脂肪酸（n-3 polyunsaturated fatty acids, n-3 PUFA）,特别是人体必需脂肪酸二十二碳六烯酸（docosahexaenoic acid, DHA）和二十碳五烯酸（eicosapentaenoic acid, EPA）。DHA和EPA在体内可以衍生出具有抗炎作用的二十碳体,如前列腺素（prostaglandins, PGs）、血栓素（thromboxanes, TX）、消退素（resolvins, Rv）、白三烯（leukotrienes, LTs）和其他氧化衍生物等。且鱼油补充有助于人体炎性衰老相关因子（血清 IL-6、IL-1、TNF-α及 CRP）水平的降低,并对炎性衰老相关疾病具有积极预防效果。本文系统介绍了DHA、EPA二十碳体的衍生及与二十碳四烯酸（arachidonic acid, AA）衍生的关系。同时基于鱼油补充与人体炎性衰老相关因子的关系,总结了膳食鱼油在改善中老年人群心血管疾病、类风湿关节炎、认知障碍及2型糖尿病的作用。已有数据显示,鱼油在降低炎性衰老因子,血脂异常改善和类风湿性关节炎症状减轻方面具有积极的临床效果。但是,在认知功能障碍和2型糖尿病改善方面,尚缺乏充分的治疗或者预防作用相关证据。     

EFFECTS OF DIETARY 18:3 N-3 TRANS ISOMERS ON THE Δ6 DESATURATION OF α-LINOLENIC ACID

Trans isomers of polyunsaturated fatty acids (PUFA) are formed during heat treatment of oils. In the present work, the effect of dietary geometrical isomers of α-linolenic acid (18:3 n-3) on the Δ6 desaturation of all cis 18:3 n-3 was investigated, using rat liver microsomes. The desaturation rates were higher in microsomes from animals fed a cis n-3 deficient diet, as compared to those from the control group or those from rats fed 18:3 n-3 and its trans isomers. These data and the incorporation of long chain trans PUFA in microsomal lipids suggest that geometrical isomers of 18:3 n-3 are probably slowly desaturated and elongated into long chain trans polyunsaturated fatty acids compared to 18:3 n-3.     

Endogenous production of n-3 and n-6 fatty acids in mammalian cells

Polyunsaturated fatty acids (PUFA) are important components of mammalian diets, and the beneficial effects of n-3 PUFA on human development and cardiovascular health have been well documented. Caenorhabditis elegans is one of the few animals known to be able to produce linoleic (LA, 18:2n-6) and alpha-linolenic (ALA, 18:3n-3) essential fatty acids. These essential PUFA are generated by the action of desaturases that successively direct the conversion of monounsaturated fatty acids (MUFA) to PUFA. The cDNA coding sequences of the C. elegans Delta(12) and n-3 fatty acid desaturases were each placed under the control of separate constitutive eukaryotic promoters and simultaneously introduced into HC11 mouse mammary epithelial cells by adenoviral transduction. Phospholipids from transduced cells showed a significant decrease in the ratios of both MUFA:PUFA and n-6:n-3 fatty acids relative to control cultures. The fatty acid profile of transduced cellular phospholipids revealed significant decreases in MUFA and arachidonic acid (20:4n-6), and increases in LA, ALA, and eicosapentaenoic acid (20:5n-3). The fatty acid composition of triacylglycerols derived from transduced cells was similarly, but less dramatically, affected. These results demonstrate the functionality of C. elegans fatty acid desaturase enzymes in mammalian cells. Expression of these desaturases in livestock might act to counterbalance the saturating effect that rumen microbial biohydrogenation has on the fatty acid profile of ruminant products, and allow for the development of novel, land-based dietary sources of n-3 PUFA.     

新时期国民膳食脂质摄入推荐的几点建议（网络首发、推荐阅读）

随着社会经济水平的快速提高,我国居民膳食结构发生了明显的改变。膳食脂质是膳食结构的重要组成部分,其推荐摄入量对改善居民膳食结构,实现新时期健康中国建设目标的都有着重要影响。对中国居民膳食脂质参考摄入量的修订提出几点建议。（1）我国18岁及以上居民的膳食脂肪供能比可接受范围上限（U-AMDR）是30%E,低于欧盟和北美国家的35%E。有学者建议提高我国成年人膳食脂肪供能比的U-AMDR,但仍缺乏足够的证据,暂不宜做修改。然而,考虑到老年人需要高能量和营养密度膳食的特点,应考虑提高老年人膳食脂肪的U-AMDR。（2）一些研究表明n-6/n-3多不饱和脂肪酸比值（n-6/n-3PUFA）与多种慢性非传染性疾病发生风险密切相关。我国居民膳食中n-6/n-3PUFA比值的平均值达到8.6,在某些人群中甚至更高。因此,建议将膳食中n-6/n-3PUFA比值的推荐值纳入新版膳食脂质参考摄入量推荐中。（3）尽管开展了大量研究,但膳食胆固醇摄入量与心血管疾病等多项慢性疾病发生结局之间的关系仍不明确。我国城市居民平均每日胆固醇摄入量为264.0 mg,农村居民为168.8 mg,处于正常范围。基于目前的研究证据,仍无法针对一般成年人群制订膳食胆固醇摄入限量。对于心脑血管疾病等慢性疾病的患者,建议参考相应疾病指南中膳食胆固醇摄入量的推荐。     

Effect of the types of dietary fats and non-dietary oils on bone metabolism

Nutrients beyond calcium and vitamin D have a role on bone health, and in treatment and prevention of osteoporosis. Quality and quantity of dietary fat may have consequences on skeletal health. Diets with highly saturated fat content produce deleterious effects on bone mineralization in growing animals. Conversely, dietary n-3-long chain polyunsaturated fatty acids play an important role in bone metabolism and may help in prevention and treatment of bone disease. Some reports suggest a correlation between the dietary ratio of n-6 and n-3 polyunsaturated fatty acids and bone formation. Specific dietary fatty acids were found to modulate prostanoid synthesis in bone tissue and improve bone formation in both animal and clinical trials. The skeletal benefits of dietary isoprenoids are extremely documented. Higher isoprenoids intake may relate to higher bone mineral density. Dietary supplements containing fish oil, individual polyunsaturated fatty acids, and isoprenoids could be used as adjuvant with bone medications in osteoportic conditions but their doses must be considered to avoid detrimental effect of over dosages.     

Dietary fat and gut microbiota: mechanisms involved in obesity control

ABSTRACT

Obesity is a serious global health problem that is directly related to various morbidities manifestation. Intestinal dysbiosis has been implicated on obesity pathogenesis. Diet composition can alter gut microbiota, regardless of energy intake. Dietary fatty acids quality may affect gut microbiota composition, which in turn may affect host metabolic health. The mechanisms by which the different type of FFA modulate gut microbiota is yet poor elucidate and there is a lack of studies regard to this. Fatty acids may act in cell membrane, interfere with energy production, inhibit enzymatic activities, impair nutrient absorption and generate toxic compounds to cells, leading to growth inhibition or even bacterial death. The beneficial effect of the consumption of n-3 polyunsaturated fatty acids (PUFA) and conjugated linoleic acid (CLA) on microbiota, unlike n-6 PUFA and saturated fatty acids has been suggested. n-3 PUFA consumption promotes desirable changes on obese intestinal microbiota making it similar to that of normal weight individuals. More studies are needed to better understand the effect of CLA on microbiota and host health. Long term human controlled clinical trials must be conducted to allow us to understand the complex interaction between dietary fat, intestinal microbiota and obesity.     

Innovations in beef production systems that enhance the nutritional and health value of beef lipids and their relationship with meat quality

Consumers are becoming more aware of the relationships between diet and health and this has increased consumer interest in the nutritional value of foods. This is impacting on the demand for foods which contain functional components that play important roles in health maintenance and disease prevention. For beef, much attention has been given to lipids. This paper reviews strategies for increasing the content of beneficial omega-3 polyunsaturated fatty acids (PUFA) and conjugated linoleic acid (CLA) and reducing saturated fatty acids (SFA) in beef. Particular attention is given to intramuscular fat (IMF) and the relationships between fatty acid composition and key meat quality parameters including colour shelf life and sensory attributes. Despite the high levels of ruminal biohydrogenation of dietary PUFA, nutrition is the major route for increasing the content of beneficial fatty acids in beef. Feeding grass or concentrates containing linseed (rich in α-linolenic acid, 18:3n-3) in the diet increases the content of 18:3n-3 and its longer chain derivative eicosapentaenoic acid (EPA, 20:5n-3) in beef muscle and adipose tissue, resulting in a lower n-6:n-3 ratio. Grass feeding also increases docasahexaenoic acid (DHA, 22:6n-3). Feeding PUFA rich lipids which are protected from ruminal biohydrogenation result in further enhancement of the PUFA in meat with concomitant beneficial improvements in the ratio of polyunsaturated:saturated fatty acids (P:S ratio) and n-6:n-3 ratio. The main CLA isomer in beef is CLA cis-9, trans-11 and it is mainly associated with the triacylglycerol lipid fraction and therefore is positively correlated with level of fatness. The level of CLA cis-9, trans-11 in beef is related to (1) the amount of this isomer produced in the rumen and (2) synthesis in the tissue, by delta-9 desaturase, from ruminally produced trans vaccenic acid (18:1 trans-11; TVA). Feeding PUFA-rich diets increases the content of CLA cis-9, trans-11 in beef. Trans-fatty acids in foods are of rising importance and knowledge of the differential effects of the individual trans isomers is increasing. TVA is the major trans 18:1 isomer in beef and as the precursor for tissue CLA in both animals and man should be considered as a neutral or beneficial trans-isomer. Increasing the content of n-3 PUFA in beef can influence colour shelf life and sensory attributes of the meat. As the content of n-3 PUFA increases then sensory attributes such as "greasy" and "fishy" score higher and colour shelf life may be reduced. Under these situations, high levels of vitamin E are necessary to help stabilise the effects of incorporating high levels of long chain PUFA into meat. However, grass feeding not only increases n-3 PUFA and CLA but, due to its high content of vitamin E, colour shelf life is improved. It is evident that opportunities exist to enhance the content of health promoting fatty acids in beef and beef products offering opportunities to add value and contribute to market differentiation. However, it is imperative that these approaches to deliver "functional" attributes do not compromise on the health value (lipoperoxidation) or the taste of beef products.     

Correlation of animal diet and fatty acid content in young goat meat by gas chromatography and chemometrics

The meat fatty acids (FA) profiles of caprines submitted to different dietary treatments were determined by gas chromatography. The data were treated by Chemometrics to consider all variables together. The contents of saturated FA (SFA), monounsaturated FA (MUFA), polyunsaturated FA (PUFA), omega-3 (n-3) FA, and omega-6 (n-6) FA in 32 samples were analyzed. PUFA:SFA and n-6:n-3 ratios were also considered. The multivariate methods of hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to analyze the experimental results. HCA can group samples according to their basic composition, and PCA can explain the relationship among the dietary treatments according to the meat fatty acid composition. Treatment 1 presented the highest n-6 FA concentration, PUFA:SFA, and n-6:n-3 ratios, and the lowest MUFA and n-3 concentrations. Opposite results were observed for treatment 4. Treatments 2 and 3 were highly similar with differences mainly in SFA and MUFA concentrations.