素食飲食中含有非常高量之多元不飽和脂肪酸(PUFA)，雖然飲食中PUFA可降低血漿膽固醇濃度，但也可能因高量之PUFA造成低密度脂蛋白(LDL)容易被氧化，因此本研究針對台北地區長期素食者之血漿脂質與LDL被氧化能力加以探討。研究對象自臺北地區徵募了51～65歲女性素食者24名，雜食者25名；31～45歲女性素食者31名及雜食者26名；31～45歲男性素食者26名及雜食者27名。包括全素者及每天喝低脂牛奶一杯以下的奶素食者，吃素期間平均約為8.5年。評估其體位後，將受試者抽血，取血球萃取進行脂肪酸組成份分析，取血漿利用自動生化分析儀進行一般生化分析以篩選受試者，及 α-生育醇含量測定，血漿再以超高速離心分離其VLDL+IDL、LDL、HDL，各分析其膽固醇與三酸甘油酯之濃度，並將所分離之LDL於10 μM 銅離子存在下，in vitro進行LDL被氧化的敏感性測定，包括了conjugated dienes的形成lag time、TBARS (thiobarbituric acid reactive substance)、electrophoretic mobility in agarose三項；並分析LDL α-生育醇含量、與脂肪酸組成份；而後分析素食食品之油脂量和脂肪酸組成份。結果顯示(P<.05)：Plasma-TG、VLDL+IDL-TG、LDL-TG及HDL-TG在素食組與雜食組間無差異性，而Plasma-Chol、LDL-Chol、HDL-Chol與LDL-Chol/HDL-Chol比值，素食組都比雜食組明顯較低。LDL在體外以銅離子氧化產生conjugated dienes之 Lag time，素食者顯著高於雜食者，且LDL氧化2小時、3小時、4小時產生之TBARS量，素食者皆低於雜食者，如此即可說明素食者的LDL較不易被氧化。而LDL之α-生育醇的含量素食者比雜食者低，LDL的脂肪酸組成中C18:2、γ-C18:3、α-C18:3素食者高於雜食者，C16:0、C20:4、C20:5素食者低於雜食者；紅血球(RBC)的脂肪酸組成中C18:2、C20:4素食者高於雜食者，C16:1、C18:1、C20:5、C22:6素食者低於雜食者；於市售素食食品分析得知，本研究所選擇之素食自助餐廳多採用黃豆油為烹調用油，素食飲食之P/S ratio高達3.4。本研究發現我國素食者的LDL，於試管內氧化的敏感性比雜食者強。由於近年來一般認為LDL經氧化後再被吞噬細胞攝入為產生動脈粥狀硬化原因，所以若素食者之LDL具有不易被氧化的敏感性，再配合其Plasma-Chol、LDL-Chol及 LDL-Chol/HDL-Chol比值皆比雜食者較低的條件，或許可認為素食有預防心血管疾病的功能。素食者LDL脂肪酸中C18:2、C18:3所佔的比例比雜食者高，且α-生育醇量又比雜食者少的狀況下，被氧化性卻較雜食者低，較可能原因是素食飲食中含有除維生素E外其他抗氧化物較多如類黃酮化合物影響LDL的氧化，或是Eicosapentaenoic acid (C20:5)容易被氧化，而素食者LDL所含C20:5低於雜食者的關係，也可能因為素食飲食為低油、低膽固醇飲食，LDL可被氧化的總不飽和脂肪酸量較少所致。

Vegetarian diets contain large amounts of polyunsaturated fatty acids (PUFA). While these compounds can decrease plasma cholesterol levels, they also may increase the susceptibility of low density lipoproteins (LDL) to oxidation. This study intends to elucidate the effects of long-term vegetarian diets on plasma composition and LDL oxidation.Three groups living in Taipei area were studied. The first group consisted of 24 vegetarian females and 25 omnivore females ranging in age from 51 to 65 years. The second group consisted of 31 vegetarian females and 26 omnivore females ranging in age from 31 to 45 years. The third group consisted of 26 vegetarian males and 27 omnivore males ranging in age from 31 to 45 years. Among the vegetarians, the average duration of consuming vegetarian diet was 8.5 years. All vegetarians consumed no more than 1 cup of low-fat milk per day.Vegetarians of both sexes had lower plasma total cholesterol, LDL-cholesterol, HDL-cholesterol, and LDL-Chol/HDL-Chol levels than their omnivore counterparts. Plasma-triglyceride (TG) levels were identical between both groups. The lag time of conjugated diene formation in LDL oxidized against Cu2+ in vitro among vegetarians was longer than that of omnivores. TBARS formed at 2,3 and 4 hr after initiation of in vitro oxidation were significantly lower in the vegetarian groups than in the omnivore groups in all of the age and sex groups. However, there is no significant difference in agarose gel mobility of oxidized LDL of the two dietary groups. α-Tocopherol contents (μM) of plasma and LDL were lower in vegetarians than in omnivores. Linoleate content of LDL was higher in vegetarians than in omnivores, but the difference was not as large as expected. EPA (Eicosapentaenoic acid) content of LDL was lower in vegetarians due to the exclusion of fish from diets. Analysis of fatty acid composition of common dishes from vegetarian restaurants showed that soybean oil was the major cooking oil and P/S ratio reached 3.4 in vegetarian diets.The findings in this study reveal that LDL of Taiwanese vegetarians is less oxidizable in vitro. Although they consume very high polyunsaturated fat diet. The possible mechanisms account for the resistance of vegetarians'LDL to oxidation are (1) higher levels of antioxidants other than α-tocopherol such as flavonoids in vegetarian diets. (2) Higher EPA content in omnivore LDL increases its oxidizability. (3) Lower amounts of fatty acid available to be oxidized per LDL in vegetarian.