Lipids -

A general term for biological components that are insoluble in water but soluble in organic solvents such as ether and chloroform. Structurally, they include a wide variety of components. They are broadly divided into simple lipids and complex lipids, the former including fats, fatty acids, and steroids, and the latter including phospholipids, glycolipids, and lipoproteins.

In the field of food and nutrition, lipids and fats are often used as synonyms, such as lipids in food analysis tables and fats in nutrition surveys. This is because most lipids in food are fats. Triglycerides (neutral fats, or simply fats) are glycerin to which three fatty acid molecules are esterified, and almost all edible oils and fats in animals are triglycerides. Fatty acids are the components of all lipids, and in nature, they are very rarely found in free form. When animals' stored fat is used as an energy source, they are transported to each tissue through the blood as free fatty acids bound to albumin. As for steroids, cholesterol is the main component in animals, and although it is small, it exists mainly in free form as a membrane building material in all tissues. In serum, the ester form is common. In addition, there are various steroid hormones and bile acids. Phospholipids are made up of various components, but the most common structure is one in which two fatty acid molecules and one phosphorylated base component are bound to glycerin, and lecithin and cephalin (cephalin) are typical examples. Organs, brains, and nervous tissue contain more phospholipids than triglycerides. They are also abundant in eggs. Lecithin has excellent emulsifying properties and is used in food and medical applications. Sphingolipids are phospholipids that are abundant in the brain and nervous tissue. Some contain inositol. Glycolipids generally contain galactose in animals and are the main lipid component of the brain.

The digestive and absorptive rate of ordinary edible oils and fats is over 95%. Fats are subjected to the action of pancreatic lipase in the small intestine, and most of them become monoglycerides and fatty acids, which are dissolved in bile acid micelles and absorbed. After absorption, they are resynthesized into triglycerides in the small intestinal mucosal cells, enter the blood circulation system via lymph as chylomicrons, are hydrolyzed by lipoprotein lipase, and are taken up mainly in the form of fatty acids by peripheral tissues. Triglycerides consisting of medium-chain fatty acids with 8 or 10 carbon atoms are well absorbed even in cases of poor secretion of pancreatic lipase or bile acids, enter the portal vein as fatty acids and are transported directly to the liver, making them a good source of energy. Fats have a long retention time in the stomach and keep you full for a long time.

Fats have a lower specific metabolic effect (the increase in metabolic rate when food is ingested. This effect is what warms the body after eating) and a higher energy efficiency (9 kilocalories per gram) than carbohydrates and proteins. Therefore, it is an essential nutrient for a high-energy diet during heavy labor or intense exercise. As an energy source, there is almost no difference in the efficiency of various types of fats and oils. In animals, fats are stored as adipose tissue subcutaneously, in the gonads, around the kidneys, in the mesentery, etc., and play the role of an energy bank. Fats are important as a source of essential fatty acids and as a carrier of various fat-soluble vitamins (A, D, E, etc.). They are also related to the flavor of food. Japanese people currently consume nearly 60 grams of fat per person per day, which is about 26-27% of their energy, exceeding the upper limit of lipid requirements. It is important to consume vegetable and animal fats in a balanced manner. Increased fat intake has attracted attention as a cause of increased incidence of various cancers, but n-3 polyunsaturated fatty acids contained in fish oil and other sources appear to have an inhibitory effect.

Among foods, edible oils and fats have the highest lipid content, reaching 95-98% as triglycerides. Butter and margarine also contain about 80% lipid. Mayonnaise, dressings, nuts and seeds, pork, cheese, instant noodles, and potato chips are also foods rich in lipids. Ham, sausage, beef, and soy products also contain relatively high amounts of lipids. There is a wide range in lipid content even within the same food (beef has a lipid content of 1.5-30%). In general, farmed fish has more lipids than wild fish. Foods that supply the most lipids are fats and oils and meat, accounting for nearly 50% of the total, followed by seafood, eggs, beans, grains, and dairy products.

[Michihiro Kanno]

"Lipids" vol. 1-2 (1972, 1973, Kyoritsu Publishing), edited by Funahashi Saburo, Hara Ichiro, and Yamakawa Tamio ( 1972, Kyoritsu Publishing)" ▽ "Hormones and Lipid Metabolism" by Yamamoto Kiyoshi (1982, Kyoritsu Publishing)" ▽ "The Science of Lipids" by Nakamura Haruo (1990, Asakura Publishing)" ▽ "Understanding Lipid Metabolism and Its Abnormalities" (1991, Japan Axel Springer Publishing), edited by Goto Yuichiro (1991) ▽ "Chemistry and Biochemistry of Lipids" (1992, Academic Press Center), edited by the Chemical Society of Japan ▽ "Structure and Dynamics of Lipids" (1992, Kyoritsu Publishing), edited by Sato Kiyotaka and Kobayashi Masamichi (1992, Kyoritsu Publishing) ▽ "Lipids and Steroids - Techniques of Tissue and Cytochemistry" (1993, Asakura Publishing), edited by Ogawa Kazuo et al. (1993, Asakura Publishing) ▽ "The Science of Lipids" (1999, Asakura Publishing), edited by Itakura Hiroshige (1999, Asakura Publishing) "Ritter's Biochemistry, by P. Ritter, translated by Kazuo Sudo et al. (1999, Tokyo Kagaku Dojin)" ▽ "Clinical Chemistry - Essentials, by Mitsuo Ogi (2000, Kindai Publishing)" ▽ "Centenary Science as Seen in Data, by Makoto Suzuki (2000, Taishukan Shoten)" ▽ "The Latest Information on Lipid Research: Considering Appropriate Intake, by Hiroshige Itakura et al. (2000, Daiichi Publishing)" ▽ "Basic Biochemistry Experimental Methods, Vol. 5: Lipids, Carbohydrates, and Complex Carbohydrates, edited by the Japanese Biochemical Society (2000, Tokyo Kagaku Dojin)" ▽ "Biology of Sugars and Lipids, edited by Toshisuke Kawazaki, Keizo Inoue, and the Japanese Biochemical Society (2001, Kyoritsu Publishing)" ▽ "New Developments in Functional Lipids, by Osamu Suzuki and Kiyotaka Sato (2001, CMC)" ▽ "Oil Chemistry Handbook: Lipids and Surfactants, edited by the Japan Oil Chemists' Society (2001, Maruzen)" ▽ "Tracing the Functions of Biomembrane Lipids - Pioneering Their Molecular Biology" by Shibuya Isao (2002, Society Publication Center)" ▽ "Lipids and Their Stories" by Miyagawa Takaaki (2002, Saiwai Shobo)" ▽ "Platelets and Biologically Active Substances" by Ozaki Yukio (2002, Kinpodo)" ▽ "Brain Functions and Lipids" edited by Okuyama Harumi and Ando Susumu ▽ "Lipid Nutrition and Lipid Peroxidation - Is Lipid Peroxidation in the Body Injurious or Defense?" edited by Okuyama Harumi and Kikugawa Kiyomi ▽ "Fats and Oils and Allergies" edited by Okuyama Harumi and Kobayashi Tetsuyuki ▽ "Lipids and Cancer" edited by Takada Hideho and Hamasaki Tomohito ▽ "Atherosclerosis of the Heart and Cerebrovascular System and Lipid Nutrition" edited by Yanagisawa Atsuo and Hamasaki Tomohito (all 2003, Society Center Kansai)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

水に不溶でエーテル、クロロホルムなどの有機溶媒に溶ける生体成分の総称。構造的に多種類の成分が含まれる。単純脂質と複合脂質に大別され、前者には脂肪、脂肪酸、ステロイドなどが、後者にはリン脂質、糖脂質、リポタンパク質などがある。

　食品分析表では脂質、栄養調査では脂肪というように、脂質と脂肪は食品、栄養の分野ではしばしば同義語として用いられる。食品中の脂質のほとんどは脂肪であるからである。トリグリセリド（中性脂肪、あるいは単に脂肪）はグリセリンに脂肪酸3分子がエステル結合したもので、食用油脂や動物の貯蔵脂肪のほとんどすべてはトリグリセリドである。脂肪酸はすべての脂質の構成成分であり、自然界では遊離型はきわめて少ない。動物の貯蔵脂肪がエネルギー源として利用される際に、アルブミンと結合した遊離脂肪酸として血液を介して各組織へ運ばれる。ステロイドとしては、動物では量的にはコレステロールが主成分で、少量ながらすべての組織の膜構築素材としておもに遊離型で存在する。血清中ではエステル型が多い。そのほか、各種のステロイドホルモンや胆汁酸がある。リン脂質は種々の成分からなるが、グリセリンに脂肪酸2分子とリン酸化された塩基成分1分子が結合した構造のものがもっとも多く、レシチン、ケファリン（セファリン）が代表的である。臓器、脳、神経組織はトリグリセリドよりもリン脂質を多く含んでいる。卵類にも多い。レシチンは乳化性に優れ、食品や医療用に使われる。スフィンゴ脂質は脳、神経組織に多いリン脂質である。イノシトールを含むものもある。糖脂質は動物体内では一般にガラクトースを含んでおり、脳の主要な脂質成分である。

　通常の食用油脂の消化吸収率は95％以上にも及ぶ。脂肪は小腸内で膵臓(すいぞう)リパーゼの作用を受け、大部分はモノグリセリドと脂肪酸となって胆汁酸ミセルに溶解し吸収される。吸収後、小腸粘膜細胞内でトリグリセリドに再合成され、カイロミクロンとしてリンパを経由して血液循環系へ入り、リポタンパク質リパーゼにより加水分解され、脂肪酸の形で主として末梢(まっしょう)組織に取り込まれる。炭素数8、10の中鎖脂肪酸からなるトリグリセリドは膵臓リパーゼや胆汁酸の分泌不良の場合にもよく吸収され、脂肪酸として門脈へ入り直接肝臓へ運ばれるので、よいエネルギー源となる。脂肪は胃内滞留時間が長く、腹もちがよい。

　脂肪は糖質やタンパク質に比べて特異動的作用（食物を摂取したときに代謝量が増加すること。食事をとって身体が暖まるのはこの効果による）が低く、エネルギー効率が高い（1グラム当り9キロカロリー）。したがって重労働や強い運動時の高エネルギー食にはなくてはならない栄養素である。エネルギー源としては各種油脂の効率にはほとんど差はないとみなしうる。脂肪は動物体内では脂肪組織として皮下、性腺(せいせん)、腎(じん)周辺、腸間膜などに貯蔵され、エネルギー銀行の役割を果たしている。脂肪は必須(ひっす)脂肪酸の供給源、種々の脂溶性ビタミン（A、D、Eなど）の担体として重要である。食物の風味とも関係している。日本人は現在1日1人当り60グラム近くの脂肪を摂取しており、エネルギー比で約26～27％に相当し、脂質所要量の上限値を超えている。植物性および動物性の脂肪をバランスよく摂取することが大切である。脂肪摂取量の増加は種々の癌(がん)発生率を高める原因となるとして注目を集めているが、魚油などに含まれるn-3系多価不飽和脂肪酸は抑制的に働くようである。

　食品中では、食用油脂でもっとも脂質含量が高く、トリグリセリドとして95～98％にも達する。バター、マーガリンも80％程度含む。マヨネーズ、ドレッシング、種実類、豚肉、チーズ、即席麺(めん)、ポテトチップスなども脂質に富む食品である。ハム、ソーセージ、牛肉、大豆製品などにも比較的多い。同じ食品でも脂質含量に大きな幅がある（牛肉では1.5～30％）。魚類では一般に天然物より養殖物で多い。脂質を多く供給する食品は油脂類と肉類で、全体の50％近くを占め、魚介類、卵類、豆類、穀類、乳類がこれに次ぐ。

［菅野道廣］

『舟橋三郎・原一郎・山川民夫編『脂質』1～2（1972、1973・共立出版）』▽『山本清著『ホルモンと脂質の代謝』（1982・共立出版）』▽『中村治雄著『脂質の科学』（1990・朝倉書店）』▽『五島雄一郎編『わかりやすい脂質代謝とその異常』（1991・日本アクセル・シュプリンガー出版）』▽『日本化学会編『脂質の化学と生化学』（1992・学会出版センター）』▽『佐藤清隆・小林雅通著『脂質の構造とダイナミックス』（1992・共立出版）』▽『小川和朗ほか編『脂質とステロイド――組織細胞化学の技術』（1993・朝倉書店）』▽『板倉弘重著『脂質の科学』（1999・朝倉書店）』▽『P・リッター著、須藤和夫ほか訳『リッター生化学』（1999・東京化学同人）』▽『荻三男著『臨床化学――要点』（2000・近代出版）』▽『鈴木信著『データでみる百歳の科学』（2000・大修館書店）』▽『板倉弘重ほか著『脂質研究の最新情報　適正摂取を考える』（2000・第一出版）』▽『日本生化学会編『基礎生化学実験法第5巻　脂質・糖質・複合糖質』（2000・東京化学同人）』▽『川嵜敏祐・井上圭三・日本生化学会編『糖と脂質の生物学』（2001・共立出版）』▽『鈴木修・佐藤清隆著『機能性脂質の新展開』（2001・シーエムシー）』▽『日本油化学会編『油化学便覧　脂質・界面活性剤』（2001・丸善）』▽『渋谷勲著『生体膜脂質の機能を追って――その分子生物学を拓く』（2002・学会出版センター）』▽『宮川高明著『脂質ときがたり』（2002・幸書房）』▽『尾崎由基男著『血小板と生理活性物質』（2002・金芳堂）』▽『奥山治美・安藤進編『脳の働きと脂質』』▽『奥山治美・菊川清見編『脂質栄養と脂質過酸化――生体内脂質過酸化は傷害か防御か』』▽『奥山治美・小林哲幸編『油脂とアレルギー』』▽『高田秀穂・浜崎智仁編『脂質と癌』』▽『柳沢厚生・浜崎智仁編『心臓・脳血管の動脈硬化と脂質栄養』（以上、2003・学会センター関西）』

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