膳食纖維對身體的益處，最為人熟悉的除了能幫助排便外，便是降低膽固醇、對抗「三高」。而麥皮(燕麥片, oatmeal)更是當中代表。
麥皮含β-葡聚糖 減重降脂縮腰圍
麥皮含有多種營養素，如纖維素(cellulose)、澱粉、各種植物化合物等。而當中的β-葡聚糖(β-Glucan, BG)是能有效維持血脂及心血管健康的水溶性膳食纖維。β-葡聚糖不只存在於燕麥中，其他穀物如糙米、小米、蕎麥等都含β-葡聚糖。除穀物β-葡聚糖外，酵母、菇菌等都有其獨特的β-葡聚糖，其健康益處亦可有不同。我們先前亦介紹多種菇菌的β-葡聚糖對免疫的益處，大家不妨參考前文了解詳情。歐洲食品安全局(European Food Safety Authority, EFSA)在審視多份不同地區、不同時間的研究報告後指出，成年人每天至少攝取3克燕麥β-葡聚糖，能有效降低血脂。
日本有研究邀請一百名超重人士分成兩組，一組每天食用兩餐加入高β-葡聚糖(每餐2.2克) 的大麥米飯，一組吃沒有β-葡聚糖的大麥米飯。12週後發現，雖然兩組的體重、BMI、腰圍和脂肪量都有明顯下降，但有β-葡聚糖的組別效果更為明顯，腰圍和脂肪量多減少三成，血壓及反映短期脂肪代謝的游離脂肪酸(Nonesterified fatty acid, NEFA)水平亦有明顯降低。台灣亦有研究邀請三十多名超重成年人，一組吃加入β-葡聚糖的燕麥片，另一組則吃沒有β-葡聚糖的。12週後發現，吃β-葡聚糖組別的體重、BMI、體脂、低密度膽固醇(LDL)等都有明顯下降，而另一組則沒有。研究團隊指出，β-葡聚糖能吸收膽汁酸(Bile acid)，與之結合並透過排便帶出體外，引發身體運用儲存的膽固醇製造更多膽汁酸，從而降低血液的低密度膽固醇(壞膽固醇)及總膽固醇水平，而不會影響高密度膽固醇(好膽固醇)。
β-葡聚糖利腸益菌 麥皮煮熟效果更佳
β-葡聚糖除能降低低密度膽固醇外，亦能在吸收水份後和食物混合並增加稠度，從而減慢小腸吸收糖份，有助血糖穩定。作為膳食纖維，β-葡聚糖不能在小腸被人體消化吸收，到了大腸後卻能成為腸道益菌的食物。β-葡聚糖和其他膳食纖維一樣，有多種化學結構相似樣式，組合成不同形狀、大小(以分子量Molecular weight計算)的聚合物(Polymer)。而不同大小的β-葡聚糖，健康效用亦可有差異。
加拿大有研究邀請30名有輕微高血脂的受試者，每天分別吃含高或低分子量的大麥β-葡聚糖，或只吃其他心臟健康飲食早餐五週，休息四週後再換成另外一組。結果發現，吃含兩種β-葡聚糖早餐時的腰圍都有減少，而吃高分子β-葡聚糖組別的三酸甘油脂有明顯減少。腸道菌方面，高分子β-葡聚糖組別腸道中與降低腰圍及血壓有關的擬桿菌(Bacteroides)數目明顯增多，而與體重、腰圍及血壓上升有關的毛螺菌(Dorea)數目則有下降。日本則有研究以高/低分子量的β-葡聚糖或相同份量的纖維素餵食小鼠，發現雖然吃高分子β-葡聚糖組的體重增幅明顯較少，但β-葡聚糖的發酵率却是低分子β-葡聚糖較高，而有益總短鏈脂肪酸水平亦明顯較高。可見不同分子量的β-葡聚糖亦分別有其健康益處。
吃麥皮的方法甚多，由最基本的水煮、沖熱水，到冷泡牛奶或是加到菜式中(如蒸肉餅)，其實煮食方法亦對其健康效果有影響。有研究將小鼠分成多組，分別以沸水(100℃)沖泡或煮沸5分鐘的麥皮餵食30天。結果發現兩種食法都能增加身體排出膽固醇、降低血液及肝臟中的總膽固醇及三酸甘油脂(Triglycerides, TG)，而煮沸麥皮組的效果明顯比沸水沖泡的更佳。研究團隊解釋這或因煮沸過程能令麥皮的澱粉及蛋白質更易散開及釋放β-葡聚糖，令麥皮更濃稠、更易吸收膽汁酸及被腸道益菌發酵。大家在吃麥皮時，除了留意烹調方法外，亦可在離火後加入富含優質大豆蛋白及凝結芽孢桿菌BC30益生菌的益纖蛋白，為麥皮增加蛋白質之餘亦加入淡淡大豆香味，而短時間耐熱的BC30益生菌，更可增加蛋白質吸收及維持腸道健康，尢其適合減重人士、長者及關注健康的你。
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Easy Reading:
燕麥裡的「β-葡聚醣」是什麼？能幫助提高免疫力、降低膽固醇的膳食纖維該如何攝取？| 食力foodNEXT| 12-24-2024
https://www.foodnext.net/column/columnist/paper/5975894035
拆解燕麥的謬誤與迷思 | 晴報 |11-11-2020
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