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給醫生的營養最新訊息:植物為主的飲食 /轉載自Permanente期刊

原創性研究與貢獻 2013 春天
特別報導
給醫生的營養最新訊息:植物為主的飲食

作者:Philip J Tuso, MD; Mohamed H Ismail, MD; Benjamin P Ha, MD; Carole Bartolotto, Ma, RD
譯者:寂光寺
DOI: dx.doi.org/10.7812/TPP/12-085

摘要
本文的目的是介紹給醫生最新的以植物為主的飲食。儘管醫療照護成本不斷升高的問題引起全國注意,人們不健康的生活方式導致肥胖,糖尿病和心血管疾病等問題持續在蔓延,醫生們因此尋找真正有效幫助病人採取較健康的生活方式。而最有助於健康的飲食習慣是以植物性食物為主,我們定義為「養生法」,提倡天然植物性食物,不鼓勵肉類,奶製品和雞蛋以及所有經過精緻加工的食品。在此我們提出了一個案例來說明這種飲食習慣有助身體健康。 研究顯示,植物為主的飲食能有效,且低風險的降低體脂比(BMI:體重kg/身高2m)、血壓、糖化血色素和膽固醇。這種飲食方式也可以減少治療慢性疾病所需的藥物數量,和降低缺血性心臟病的死亡率。醫生應考慮建議所有的病人以植物性食物為主的飲食方式,特別是患有高血壓、糖尿病、心血管疾病或肥胖的病人。

引言
在HBO的紀錄片《 The weight of the Nation 》﹙暫譯:全民的重量﹚中提到,如果在美國你「順其自然」地跟隨大眾飲食趨勢,你最終會變得肥胖1。2011年,Witters威特爾斯報導,在美國一些地區人民的肥胖率是39%,且以每年5%的速度增長2。肥胖、糖尿病、高血壓和心血管疾病的風險,及隨之而來的併發症(如行為上的健康和生活品質的問題)往往與生活方式息息相關,尤其是飲食的選擇3。過去幾十年來為減少慢性疾病發生而提倡的所有飲食方式中,最好且也許最普遍的可能就是以植物性飲食為主的方式。

儘管已經有證據證明強壯的身體傾向來自於植物為主的飲食方式,也有研究顯示一般大眾很樂意嘗試植物性飲食4,但許多醫生仍不強調以植物性飲食作為治療慢性疾病的首要方式。這可能是因為缺乏有關這些飲食的正確認知或缺乏這方面的教育學習資源。

《國家膳食指南》中針對活躍的生活和健康飲食(可參考www.ChooseMyPlate.gov 5)提到典型的健康的一餐,由二分之一的植物性食物(非澱粉類蔬菜和水果)、四分之一的全穀類或未加工的澱粉類食物,和四分之一的瘦肉蛋白所組成。

這篇文章的目的,是審視支持以植物為主的飲食實例文獻,並提供介紹此飲食方式的指南。我們先從一個案例研究開始,最後會做結論並附上參考文獻。

案例研究
一位63歲有高血壓病史的男子跟醫生抱怨他的疲勞、噁心、肌肉痙攣。他的隨機血糖測試的結果為524毫克/分升,和糖化血色素是11.1%。經診斷為2型糖尿病。他的總膽固醇為283毫克/分升、血壓是132/66 毫米汞柱、和體脂比(BMI)為25公斤/平方米。他每天服用lisinopril賴諾普利(治療高血壓的藥)40毫克;hydrochlo-rothiazide氫氯塞治錠 (治療高血壓的藥)每天50毫克;amlodipine脈優錠(降高血壓,心絞痛的藥)每天5毫克,和atorvastatin阿托伐他汀(降膽固醇藥)每天20毫克。他的處方為metformin邁胰妥膜衣錠 (治糖尿病的藥)1000毫克每天兩次,glipizide泌樂得錠(治糖尿病的藥)每天5毫克以及睡前服用10個單位赫氏中性魚精蛋白胰島素(降血糖的藥)。他的醫生也規定他要以低鈉鹽,植物為主的飲食—每天食用不含所有動物產品、精製糖和少許的麵包、白飯、馬鈴薯和玉米片。可以吃無限量不含澱粉的蔬菜和豆類及每天最多2盎司的堅果類。他還被要求開始每天兩次15分鐘的運動。

此患者每月回診。在第16週時,從生物統計學上來看有顯著改善結果:他完全停用脈優錠、氫氯塞治錠、泌樂得錠、赫氏中性魚精蛋白胰島素。追蹤血壓為低於125/60毫米汞柱,糖化血色素進步到6.3%,並且總膽固醇進步到138毫克/分升。賴諾普利逐漸降低至每天5毫克而且他的糖尿病只以每天兩次 1000毫克的邁胰妥膜衣錠來控制。

植物為主的飲食定義
這個引人注目的例子,顯示以植物為主的飲食可以從生物統計學成果如血壓、糖尿病和脂質分佈看出其成效。糖化血色素三個月內從11.1%降低到6.3%,比預期單一使用邁胰妥膜衣錠6的治療或日常運動7 的成效還要來的更好。也觀察到在臨床實驗中鮮少遇到超過4個月期間使用少量藥物的,血壓有所改善,並且很可能與低鈉飲食和避免紅肉有所關連。由於病人不是肥胖,在節食上也沒有明顯降低體重,這戲劇性的改善似乎是與他的新飲食的品質有關。

健康的植物性飲食目的是大量增加營養豐富的植物性食物,同時盡量減少加工食品,油和動物性食物(包括乳製品和蛋)。鼓勵多吃蔬菜(熟或生)、水果、豆類、豌豆、扁豆、大豆、種子和堅果(少量)及一般的低脂脂肪8,9 。該領域的主要支持者對最佳的植物性飲食應包含哪些持不同的意見 。Ornish 歐尼斯等人建議使用少量的動物性產品如蛋白和脫脂牛奶以便戰勝疾病10,11。

Esselstyn服務於克利夫蘭診所健康機構,指導心血管預防和逆轉程序,他建議完全避免所有的動物性產品以及大豆和堅果,特別是如果患者有嚴重冠狀動脈疾病12。儘管有這些小差異,還是有證據表明廣義的以植物為主的飲食對身體有顯著的健康益處。特別指出的是,「植物為主」 這個術語有時可以互換為「素食」或「純素」 。基於道德或宗教(不是基於增進身體健康)的理由而採用素食或全素飲食,並不一定保證能指向健康。 因此,重要的是要知道相關飲食的具體定義及確定病人的飲食細節,而不是單純假設它是如何的健康。以下是一個典型的限制動物產品飲食的簡要總結。關鍵的區別是,大多數的飲食是以其不包含的食物來定義,然而植物為主的飲食則是以它包含的內容物來定義。

Vegan (or total vegetarian) 純素(或完全素食):不包括所有動物產品,特別是肉類、海鮮、家禽、蛋和奶製品。不需要食用天然食品或限制脂肪或精製糖。

Raw food, vegan 生食,純素:與素食主義有相同的食物排除類別以及排除所有烹煮溫度超過華氏118°F的熟食品(約攝氏47.7°C)。

Lacto-vegetarians奶素 : 不包括蛋、肉、海鮮、家禽、包括牛奶產品。

Ovo-vegetarian蛋素:不包括肉類、海鮮、家禽和奶製品,包括雞蛋。

Lacto-ovo vegetarian奶蛋素:不包括肉類、海鮮、家禽,包括雞蛋和奶製品。

Mediterranean 地中海式:類似於以天然食品、植物為主的飲食習慣,但允許少量雞肉、奶製品、蛋,和每月一次或兩次的紅肉。鼓勵食用魚和橄欖油。沒有限制脂肪。

Whole-foods, plant-based, low-fat天然食品、植物為主、低脂肪: 鼓勵天然的植物性食物,尤其是蔬菜、水果、豆類和種籽和堅果 (少量)。為了最大的健康效益,這樣的飲食限制動物產品。總量脂肪一般是限制的。

植物為主的飲食之好處
我們飲食的目的應該是要改善健康。在本段落中,我們將回顧文獻的關鍵內容,證明以植物為主的飲食之好處。我們會審視包括現有的研究,涵蓋純素、素食和地中海式飲食。

肥胖
2006年,審查87篇研究報告後,作者Berkow和 Barnard 13在《營養評價》 中提出純素或素食的飲食對降低體重是非常有效的。他們還發現該素食人群的心臟病,高血壓、糖尿病和肥胖發病率較低。另外,他們的審查也建議,素食者的體重下降不是依賴於運動,而且每週大約是下降一磅的比率(約0.45公斤) 。作者進一步說明純素飲食飯後較能燃燒更多卡路里,相對來說,因為食物被儲存為脂肪13,非素食飲食可能導致較少的熱量被然燒。

Farmer等人14建議相較於其他含肉飲食,素食飲食可能較有助於管理體重,並且可能更有營養。在他們的研究中發現,素食者比食肉者更苗條。也發現素食者攝取更多的鎂、鉀、鐵、硫胺素、核黃素、葉酸和維他命及較低的脂肪總量。作者的結論是:素食飲食不但營養高且可推薦用於體重管理,並且不影響飲食品質14。

2009年,Wang 和Beysoun15分析1999-2004年衛生與營養調查的全國代表性的數據。研究的目的是分析肉類消費和肥胖之間的關連。用線性和物流回歸分析,他們發現,肉類消費和肥胖呈現正相關15。

歐洲前瞻性調查癌症和營養的牛津分部,針對在英國超過五年時間的肉食、魚食、素食和純素食的男性和女性,評估其體重和BMI變化。五年的研究中,這些人當中飲食改變成少量的動物性食物的人,每年增加的體重是最低的。該研究還報導了在年齡調整體重指數有顯著的差異 ,肉食者具有最高的BMI,而素食主義者則是最低的16。基督復活安息日會健康研究也有類似的結果報告17。

根據Sabaté and Wien 18,流行病學研究表明,不論是成年人及兒童,素食飲食與降低BMI、降低肥胖趨勢是相關連的。關於成人素食飲食研究的整合分析估計,體重減少的差異,男性為7.6公斤,女性為3.3公斤,BMI因此降低2個指數。同樣地,與非素食者相較,素食兒童比較結實,而且他們的BMI差異在青春期是越大的。探索超重風險和食物類別及飲食模式的研究表明,植物為主的飲食似乎是預防兒童肥胖的明智方法。以植物為主的飲食是低能量密度和高複合糖、纖維以及水,可以增加飽足感和靜息能量的消耗18。此研究結論是以植物為主的飲食模式應該是對健康最好的。

糖尿病
比起非以植物為主的飲食,以植物為主的飲食之益處是預防及控制糖尿病。基督復活安息日會健康研究發現,素食者得糖尿病的風險僅是非素食者的一半不到19。2008年,Vang等人20 報導,非素食者比素食者有74%的可能發展為糖尿病超過17年的時間。2009年,涉及超過60,000名男性和女性的一個研究發現,糖尿病中的個人的患病率,純素飲食為2.9%,非素食者則為7.6%17。低脂肪、以植物為主的飲食並且無肉或少肉飲食可能有助於預防和治療糖尿病,大概是因其改善胰島素敏感性和降低胰島素抵抗。

Barnard等人21 在2006年報告一項隨機臨床試驗,關於採用低脂純素飲食和根據美國糖尿病組織的飲食指導的比較結果。採用低脂純素飲食的人其糖化血色素減少 1.23點,而遵循美國糖尿病組織的飲食指導的人則是0.38點。此外,43%的低脂純素飲食的人能減少用藥,而遵循美國糖尿病組織的飲食指導的人則是26%18 。

心臟疾病
在The Lifestyle Heart Trial 生活方式及心臟試驗的研究中,Ornish10發現82%患有心臟疾病且依據他的生活指導安排的病人,其動脈粥狀硬化有某種程度的復原。甚至對嚴重的冠狀動脈粥狀硬化的復原只要一年的時間,全面改變生活方式似乎是促進因素。他的植物為主的食物療法中,熱量的10%來自脂肪,15%至20%來自蛋白質,70%至75%來自碳水化合物,膽固醇被限制在每天5毫克。有趣的是,與對照組的53%有動脈粥樣硬化的進展。經過5 年,狹窄症的實驗組從37.8%下降至34.7% (7.9%相對改善)。對照組經歷了狹窄症的進展從46.1%到57.9%(27.7%相對惡化)。低密度脂蛋白在1年時已減少40%,而且5年後保持在20% 少於基準線。這些降低情況類似於降脂藥物的效果10,11。

里昂飲食心臟研究一個前瞻、隨機、二級預防化的試驗中,de Lorgeril發現干預組(在第27個月)有73%減少冠心病事件並且在所有原因的死亡率降低了70%。干預組的地中海式飲食中包含比肉還更多的植物性食物,蔬菜、水果、魚。牛油和奶油換成了菜籽油的人造奶油。菜籽油和橄欖油是唯一建議的脂肪來源22。

1998年,有一份協同分析採用 了5篇前瞻性研究的原始數據進行審查,並被發表在《公共健康營養雜誌》上。 其中比較了素食者和非素食者之特異的缺血性心臟疾病死亡率的比例。素食者在缺血性心臟疾病死亡率相對非素食者減少24%23。缺血性心臟病的風險較低可能與攝取少肉的人膽固醇較低有關連24。

雖然素食飲食與幾種慢性疾病有低風險的關連,但不同類型的素食者在健康上也可能不一定有相同的效果。關鍵是要吃得健康,而不是只是純素或素食飲食就夠了25。

高血壓
2010年,美國飲食指標指導委員會進行了文獻審查,為了研究文獻資料中關於飲食模式對成人血壓的影響。證實素食飲食和降低血壓有相關26。一個隨機交叉試驗發現了一種日本人的飲食(低鈉和以植物為主) 顯著降低收縮壓27。

死亡
美國飲食指標指導委員會進行了2010年的文獻審查,確定了植物為主的飲食在中風、心血管病和成人的總死亡率的影響。他們發現,植物為主的飲食比非植物為主的飲食能降低心臟血管疾病和死亡率26。

植物為主的飲食降低死亡率的最主要原因是減少食用紅肉28。幾項研究已經證明了避免食用紅肉的好處,紅肉具有增加所有死亡及心血管疾病死亡率的關聯性29。攝取少量肉類比較能長壽一直都有相關30。

2012年,Huang等人31,以素食者和非素食者之間心血管疾病的死亡率執行整合分析研究。他們只取相對風險及符合95%的信賴區間的研究報告。7篇研究報告共有124,706參加者進行了分析。 顯示素食者相對非素食者有低於29%的缺血性心臟疾病的死亡率31。

植物為主的飲食之健康關注問題

蛋白質
一般來說,以植物為主的飲食的患者並沒有缺乏蛋白質的風險。蛋白質是由氨基酸組成的,其中一些被稱為必需氨基酸, 是人體不能自行合成, 必須從食物中獲得。而必需氨基酸存在於肉類、乳製品和蛋以及許多植物性食物,如藜麥32。必需氨基酸也可以從攝取某些組合的植物性食物而得到。 例如,糙米和豆類、鷹嘴豆泥搭配全麥皮塔。因此,均衡的植物為主的飲食可以提供足夠的必需氨基酸和防止蛋白質缺乏症33。

大豆和大豆製成的食品是蛋白質的良好來源,並且可以幫助降低在血液中的低密度脂蛋白34,並減少臀部骨折的風險35 和一些癌症。

《美國醫療協會雜誌 》的一項研究36報導,患有乳腺癌的婦女經常食用大豆相較於很少或不食用大豆的婦女降低32%乳腺癌復發的風險,並降低29%的死亡風險36。一份發表在《美國臨床營養學雜誌》的14項研究報告的分析,顯示增加大豆攝取剪少了26%前列腺癌的風險37。

由於豆製品有雌激素,有乳腺癌病史的女性應該與其腫瘤科醫師討論大豆食品攝取量。此外,過度加工大豆做的肉類替代品往往高度分離大豆蛋白質和其他成分,這可能不如少量加工的大豆產品來得健康(如豆腐、天貝、豆漿)。


植物為主的飲食含鐵,但鐵在植物中相較肉類來說屬較低的生物利用度。植物性食物中含豐富鐵質包括四季豆、黑豆、黃豆、菠菜、葡萄乾、腰果、燕麥片,高麗菜和番茄汁38。對遵循植物為主的飲食並攝取很少或不攝取動物產品的人來說,鐵的儲存可能比較低。然而,美國飲食協會指出對遵循植物為主的飲食的人來說,缺鐵性貧血卻是罕見的39。

維他命B12
血液的生成和細胞分裂是需要維他命B12 的。 缺乏維他命B12 是一個很嚴重的問題,可以導致巨紅細胞性貧血和不可逆轉的神經損傷。維他命B12 是由細菌製造的,而不是植物或動物。遵循植物為主且不食用任何動物產品的人可能容易缺乏維他命B1240 ,他們必須補充含有維他命B12或者強化維他命B12的食物41。

鈣和維他命D
在均衡、精心策劃、植物為主的飲食中鈣是足夠的。不吃含有高鈣的植物的人可能處於骨質礦化和骨折的危險之中。 然而,研究表明,骨折的風險不論對素食者和非素食者來說是差不多的。促進骨骼健康的關鍵是攝入足夠的鈣,這似乎與飲食喜好不相干42。 一些重要的鈣質來源包括豆腐,芥末和蕪菁塊根葉 ,白菜和甘藍。菠菜和其他一些含有鈣的植物,雖然豐富,但勢必會含草酸鹽,因此,很難被身體吸收43。

一般人缺乏維他命D是常見的。可以加強植物為主的產品如豆漿和麥片,以提供足夠的維他命D來源44。有骨質礦化風險的人及被發現缺乏維他命D的人,建議服用補給品。

脂肪酸
人類身體健康必須攝取必需脂肪酸,因為我們的身體沒有合成脂肪酸。只有兩種必需脂肪酸是已知的: 亞油酸 ( omega-6 脂肪酸)和α-亞麻酸 (omega-3 脂肪酸)。 其他三個脂肪酸只是條件式的必需: 棕櫚油酸 (單元不飽和脂肪酸) ,十二烷酸(飽和脂肪酸), 和γ-亞麻酸 ( omega-6 脂肪酸)。缺乏必需脂肪酸可能會使皮膚,頭髮,指甲的看起來異常45。

素食者最有可能缺少的脂肪酸是omega-3(n-3脂肪酸)。也可能很缺乏植物性的 omega-3脂肪酸,α-亞麻酸的攝取。充足攝入n-3脂肪酸能降低心臟疾病及中風的發生率。其實包括亞麻籽,亞麻籽油,核桃,和菜籽油46 都是n-3脂肪良好來源的食物。。

結論
一個健康的、植物為主的飲食要求也須妥善規劃,相關閱讀標籤和遵守紀律。可以推薦想要遵循植物為主的飲食的患者食用各種水果和蔬菜,包括大豆、豆類、種子、堅果和粗糧,並且避免或限制動物性食品、補充脂肪、油和精製且加工的碳水化合物。患者決定開始以植物性為主的飲食後最大好處就是減少以藥物治療各種慢性疾病、降低體重、降低患癌症 的風險,和降低缺血性心臟疾病的死亡風險。

植物為主的飲食不是一個孤注一擲的計劃,而是針對每一個人訂做的一種生活方式,對肥胖、2型糖尿病、高血壓、脂質異常或心血管疾病的人來說也許特別有益。越能夠堅持持之以恆就越能體會到減少動物產品消費的實際好處。不能手術或嚴重的冠狀動脈疾病的人最好能實行嚴格的植物為主、少量或完全沒有動物產品的飲食對有高血壓或冠狀動脈疾病或中風的家族病史的人可開以低鈉鹽、植物為主的飲食處方。有肥胖和糖尿病的患者也能從適量的水果和蔬菜及最低的低脂肪動物性產品這類以植物為主的飲食中受益。重度肥胖可能需要諮詢及低熱量飲食或極低熱量飲食的初期管理和醫生團隊的監督。腎病患者可能需要植物為主的飲食並且有其特殊的限制,例如要注意含量高的鉀和磷的水果和蔬菜。最後,甲狀腺疾病患者需要小心食用輕微的致甲狀腺腫素的植物,如大豆、生的十字花科蔬菜,地瓜和玉米。這些患者應該被告知要烹調這些蔬菜能致甲狀腺腫素失活。

醫生們應該提倡,是時候該擺脫只以術語如純素和素食來看待飲食習慣 ,並多建議健康、天然、植物性食物為主的飲食習慣(主要是水果和蔬菜)和減少到最低量的肉類、雞蛋和奶製品。醫師本身應該先了解這些概念,則可以教導其他工作人員和病人。

應該將合格的營養師列入醫護團隊中,職責是為慢性疾病患者設計植物為主的飲食,而對於服用多種藥物的慢性疾病患者,需要密切監測是否低血糖值、低血壓或急速體重下降。如果出現這些情況,醫生可能需要調整藥物。除此以外,如這裡所展示的,對某些藥物的需求是可以完全消除的。雖然失誤風險可能較低,醫護團隊仍需要知道,對於執行嚴謹的植物為主飲食的病人,還是可能需要監測某些營養物不足之處,如上文所述。

本文的目的是幫助醫生了解以植物為主的飲食之潛在利益,以期最終能共同創造以植物為主的營養為基礎的飲食習慣之社會轉變。至少從文獻中適度質量的證據,及與非以植物為主的飲食相比較,植物為主的飲食顯著的與體重下降及心血管疾病和死亡率的風險降低有關連。這些數據表明植物為主的飲食可能是一個預防和治療慢性疾病實用的解決方法。

為了使我們的患者和醫護團隊將以植物為主的飲食成為新常態,需要更進一步研究,以找到方法。我們就算不能治癒慢性疾病,但可能能夠藉由改變我們的飲食去預防和控制它們。 隨著不斷教育並持續監測,我們可以改善健康結果。 至於不樂意支持他人改變的家庭和其他同事,也是個需要去克服的挑戰。

為採納植物為主的飲食和有規律的運動計劃之目標, 我們應該邀請我們的同事,患者及家屬共享決策過程。 我們應該邀請健康服務團隊來完成一個健康飲食和積極生活的課程。也要鼓勵人員熟知以植物為主的食物營養。最後,我們應該鼓勵以注重績效為主的評量,可以包括:
1.醫生完成營養學課程的比例,包括討論植物為主的飲食和運動的好處;
2.醫院,餐廳和醫師會議設施,其提供之餐點應與「以植物為主的飲食」理念一致的比例;
3.肥胖患者在醫師小組裡完成針對植物為主的飲食之體重管理和營養學的比例;
4.高血壓、糖尿病、高血脂或心血管疾病患者在醫師小組裡完成針對植物為主的飲食之營養學的比例。

很多時候,醫生忽略了良好的營養之潛在益處,只是迅速給予處方,而不是透過健康的飲食和積極的生活讓患者有機會改善自己的疾病。如果我們要減緩肥胖流行和減少慢性併發症疾病,我們必須考慮改變我們的文化思維方式,從「活著是為了吃」到「吃是為了活著」。未來的醫療保健演變為以預防和治療疾病為中心,不是在藥物提供或手術操作上,而是在水果和蔬菜上。

公開聲明
作者(們)完全沒有利益涉入及牽扯。

感謝
Kathleen Louden, ELS, of Louden Health 提供了編輯援助。

參考文獻請參照以下原文版

The Permanente Journal/ Spring 2013/ Volume 17 No. 2 61
Original RESEARCH & CONTRIBUTIONS
Special Report
Nutritional Update for Physicians: Plant-Based Diets
Philip J Tuso, MD; Mohamed H Ismail, MD; Benjamin P Ha, MD; Carole Bartolotto, MA, RD Perm J 2013 Spring;17(2):61-66
dx.doi.org/10.7812/TPP/12-085
Philip J Tuso, MD, is the Regional Co-Lead for the Complete Care Program of the Southern California Permanente
Medical Group and the National Physician Lead for the Care Management Institute’s Total Health Program. E-mail:
phillip.j.tuso@kp.org. Mohamed H Ismail, MD, is a Physician at the Riverside Medical Center in CA. E-mail:
mohamed.h.ismail@kp.org. Benjamin P Ha, MD, is the Associate Area Medical Director for Family Medicine at the
Bakersfield Medical Center in CA. E-mail: benjamin.p.ha@kp.org. Carole Bartolotto, MA, RD, is a Senior Consultant for
Regional Health Education for the Southern California Permanente Medical Group. E-mail: carole.a.bartolotto@kp.org.

Abstract
The objective of this article is to present to physicians an update on plant-based diets. Concerns about the rising cost of health care are being voiced nationwide, even as unhealthy lifestyles are contributing to the spread of obesity, diabetes, and cardiovascular disease. For these reasons, physicians looking for cost-effective interventions to improve health outcomes are becoming more involved in helping their patients adopt healthier lifestyles. Healthy eating may be best achieved with a plant-based diet, which we define as a regimen that encourages whole, plant-based foods and discourages meats, dairy products, and eggs as well as all refined and processed foods. We present a case study as an example of the potential health benefits of such a diet. Research shows that plantbased diets are cost-effective, low-risk interventions that may lower body mass index, blood pressure, HbA1C, and cholesterol levels. They may also reduce the number of medications needed to treat chronic diseases and lower ischemic heart disease mortality rates. Physicians should consider recommending a plant-based diet to all their patients, especially those with high blood pressure, diabetes, cardiovascular disease, or obesity.

Introduction
In the HBO documentary The Weight of the Nation, it was noted that if you“go with the flow”in the US, you will eventually become obese.1 In 2011, Witters reported that in some areas of the country, the rate of obesity is 39% and is increasing at a rate of 5% per year.2 Risks of obesity, diabetes, hypertension, and cardiovascular disease, along with their ensuing complications (eg, behavioral health and quality-of-life problems) often go hand-in-hand and are strongly linked to lifestyle, especially dietary choices.3 Of all the diets recommended over the last few decades to turn the tide of these chronic illnesses, the best but perhaps least common may be those that are plant based.

Despite the strong body of evidence favoring plant-based diets, including studies showing a willingness of the general public to embrace them,4 many physicians are not stressing the importance of plantbased diets as a first-line treatment for chronic illnesses. This could be because of a lack of awareness of these diets or a lack of patient education resources. National dietary guidelines for active living and healthful eating are available at www.ChooseMyPlate.gov.5 A typical healthful plate of food is 1/2 plant foods (nonstarchy vegetables and fruits), 1/4 whole grains or unprocessed starchy food, and 1/4 lean protein. The goal of this article is to review the evidence supporting plant-based diets and to provide a guideline for presenting them to patients. We start with a case study and conclude with a review of the literature.

Case Study
A 63-year-old man with a history of hypertension presented to his primary care physician with complaints of fatigue, nausea, and muscle cramps. The result of a random blood glucose test was 524 mg/dL, and HbA1C was 11.1%. Type 2 diabetes was diagnosed. His total cholesterol was 283 mg/dL, blood pressure was 132/66 mmHg, and body mass index (BMI) was 25 kg/m2. He was taking lisinopril, 40 mg daily; hydrochlorothiazide, 50 mg daily; amlodipine, 5 mg daily; and atorvastatin, 20 mg daily. He was prescribed metformin, 1000 mg twice daily; glipizide, 5 mg daily; and 10 units of neutral protamine Hagedom insulin at bedtime. His physician also prescribed a low-sodium, plant-based diet that xcludedall animal products and refined sugars and limited bread, rice, potatoes, and tortillas to a single daily serving. He was advised to consume unlimited nonstarchy vegetables, legumes, and beans, in addition to up to 2 ounces of nuts and seeds daily. He was also asked to begin exercising 15 minutes twice a day. The patient was seen monthly in his primary care clinic. Over a 16-week period, significant improvement in biometric outcome measures was observed. He was completely weaned off of amlodipine, hydrochlorothiazide, glipizide, and neutral protamine Hagedorn insulin. Follow-up blood pressure remained below 125/60 mmHg, HbA1C improved to 6.3%, and total cholesterol improved to 138 mg/dL. Lisinopril was gradually decreased to 5 mg daily and his diabetes is controlled with metformin alone, 1000 mg twice daily.

Definitions of Plant-Based Diets
The presented case is a dramatic example of the effect a plant-based diet can have on biometric outcomes like blood pressure, diabetes, and lipid profile. The reduction in HbA1C from 11.1% to 6.3% in 3 months is much better than would be expected with monotherapy with metformin6 or daily exercise.7 The improvement in blood pressure observed over a 4-month period with few medications is also rarely encountered in clinical practice and is likely related to a low-sodium diet and the avoidance of red meat. Because the patient was not obese and did not have significant weight loss with the diet, the dramatic improvements appear to be related to the quality of his new diet.

A healthy, plant-based diet aims to maximize consumption of nutrient-dense plant foods while minimizing processed foods, oils, and animal foods (including dairy products and eggs). It encourages lots of vegetables (cooked or raw), fruits, beans, peas, lentils, soybeans, seeds, and nuts (in smaller amounts) and is generally low fat.8,9 Leading proponents in the field have varying opinions as to what comprises the optimal plant-based diet. Ornish et al recommends allowing animal products such as egg whites and skim milk in small amounts for reversal of disease.10,11 Esselstyn, who directs the cardiovascular prevention and reversal program at the Cleveland Clinic Wellness Institute, recommends completely avoiding all animal-based products as well as soybeans and nuts, particularly if severe coronary artery disease is present.12

Despite these smaller differences, there is evidence that a broadly defined plantbased diet has significant health benefits. It should be noted that the term plantbased is sometimes used interchangeably with vegetarian or vegan. Vegetarian or vegan diets adopted for ethical or religious reasons may or may not be healthy. It is thus important to know the specific definitions of related diets and to ascertain the details of a patient’s diet rather than making assumptions about how healthy it is. The following is a brief summary of typical diets that restrict animal products. A key distinction is that although most of these diets are defined by what they exclude, the plant-based diet is defined by what it includes.

Vegan (or total vegetarian): Excludes all animal products, especially meat, seafood, poultry, eggs, and dairy products. Does not require consumption of whole foods or restrict fat or refined sugar.
Raw food, vegan: Same exclusions as veganism as well as the exclusion of all foods cooked at temperatures greater than 118°F.
Lacto-vegetarian: Excludes eggs, meat, seafood, and poultry and includes milk products.
Ovo-vegetarian: Excludes meat, seafood, poultry, and dairy products and includes eggs.
Lacto-ovo vegetarian: Excludes meat, seafood, and poultry and includes eggs and dairy products.
Mediterranean: Similar to wholefoods, plant-based diet but allows small amounts of chicken, dairy products, eggs, and red meat once or twice per month. Fish and olive oil are encouraged. Fat is not restricted.
Whole-foods, plant-based, low-fat: Encourages plant foods in their whole form, especially vegetables, fruits, legumes, and seeds and nuts (in smaller amounts). For maximal health benefits this diet limits animal products. Total fat is generally restricted.

Benefits of Plant-Based Diets
The goal of our diet should be to improve our health. In this section, we will review the literature for key articles that demonstrate the benefits of plant-based diets. Our review consists of existing studies that include vegan, vegetarian, and Mediterranean diets.

Obesity
In 2006, after reviewing data from 87 published studies, authors Berkow and Barnard13 reported in Nutrition Reviews that a vegan or vegetarian diet is highly effective for weight loss. They also found that vegetarian populations have lower rates of heart disease, high blood pressure, diabetes, and obesity. In addition, their review suggests that weight loss in vegetarians is not dependent on exercise and occurs at a rate of approximately 1 pound per week. The authors further stated that a vegan diet caused more calories to be burned after meals, in contrast to nonvegan diets which may cause fewer calories to be burned because food is being stored as fat.13

Farmer et al14 suggest that vegetarian diets may be better for weight management and may be more nutritious than diets that include meat. In their study, they showed that vegetarians were slimmer than their meat-eating counterparts. Vegetarians were also found to consume more magnesium, potassium, iron, thiamin, riboflavin, folate, and vitamins and less total fat. The authors conclude that vegetarian diets are nutrient dense and can be recommended for weight management without compromising diet quality.14

In 2009, Wang and Beysoun15 analyzed the nationally representative data collected in the 1999-2004 National Health and Nutrition Examination Survey. The aim of their study was to analyze the associations between meat consumption and obesity. Using linear and logistic regression analyses, they showed that there was a positive association between meat consumption and obesity.15 The Oxford component of the European Prospective Investigation into Cancer and Nutrition assessed changes in weight and BMI over a five-year period in meateating, fish-eating, vegetarian, and vegan men and women in the United Kingdom. During the five years of the study, mean annual weight gain was lowest among individuals who had changed to a diet containing fewer animal foods. The study also reported a significant difference in age-adjusted BMI, with the meat eaters having the highest BMI and vegans the lowest.16 Similar results were reported by the Adventist Health Study.17

According to Sabate and Wien,18 “Epidemiologic studies indicate that vegetarian diets are associated with a lower BMI and a lower prevalence of obesity in adults and children. A meta-analysis of adult vegetarian diet studies estimated a reduced weight difference of 7.6 kg for men and 3.3 kg for women, which resulted in a 2-point lower BMI. Similarly, compared with nonvegetarians, vegetarian children are leaner, and their BMI difference becomes greater during adolescence. Studies exploring the risk of overweight and food groups and dietary patterns indicate that a plant-based diet seems to be a sensible approach for the prevention of obesity in children. Plant-based diets are low in energy density and high in complex carbohydrate, fiber, and water, which may increase satiety and resting energy expenditure.”18 The authors conclude that plant-based dietary patterns should be encouraged for optimal health.

Diabetes
Plant-based diets may offer an advantage over those that are not plant based with respect to prevention and management of diabetes. The Adventist Health Studies found that vegetarians have approximately half the risk of developing diabetes as nonvegetarians.19 In 2008, Vang et al20 reported that nonvegetarians were 74% more likely to develop diabetes over a 17-year period than vegetarians. In 2009, a study involving more than 60,000 men and women found that the prevalence of diabetes in individuals on a vegan diet was 2.9%, compared with 7.6% in the nonvegetarians.17 A low-fat, plant-based diet with no or little meat may help prevent and treat diabetes, possibly by improving insulin sensitivity and decreasing insulin resistance. Barnard et al21 reported in 2006 the results of a randomized clinical trial comparing a low-fat vegan diet with a diet based on the American Diabetes Association guidelines. People on the low-fat vegan diet reduced their HbA1C levels by 1.23 points, compared with 0.38 points for the people on the American Diabetes Association diet. In addition, 43% of people on the low-fat vegan diet were able to reduce their medication, compared with 26% of those on the American Diabetes Association diet.18

Heart Disease
In the Lifestyle Heart Trial, Ornish10 found that 82% of patients with diagnosed heart disease who followed his program had some level of regression of atherosclerosis. Comprehensive lifestyle changes appear to be the catalyst that brought about this regression of even severe coronary atherosclerosis after only 1 year. In his plant-based regimen, 10% of calories came from fat, 15% to 20% from protein, and 70% to 75% from carbohydrate, and cholesterol was restricted to 5 mg per day.

Interestingly, 53% of the control group had progression of atherosclerosis. After 5 years, stenosis in the experimental group decreased from 37.8% to 34.7% (a 7.9% relative improvement). The control group experienced a progression of stenosis from 46.1% to 57.9% (a 27.7% relative worsening). Low-density lipoprotein had decreased 40% at 1 year and was maintained at 20% less than baseline after 5 years. These reductions are similar to results achieved with lipid-lowering medications.10,11

In the Lyon Diet Heart Study, a prospective, randomized, secondary prevention trial, de Lorgeril found that the intervention group (at 27 months) experienced a 73% decrease in coronary events and a 70% decrease in all-cause mortality. The intervention group’s Mediterranean-style diet included more plant foods, vegetables, fruits, and fish than meat. Butter and cream were replaced with canola oil margarine. Canola oil and olive oil were the only fats recommended.22

In 1998, a collaborative analysis using original data from 5 prospective studies was reviewed and reported in the journal Public Health Nutrition. It compared ischemic heart disease-specific death rate ratios of vegetarians and nonvegetarians. The vegetarians had a 24% reduction in ischemic heart disease death rates compared with nonvegetarians.23 The lower risk of ischemic heart disease may be related to lower cholesterol levels in individuals who consume less meat.24

Although vegetarian diets are associated with lower risk of several chronic diseases, different types of vegetarians may not experience the same effects on health. The key is to focus on eating a healthy diet, not simply a vegan or vegetarian diet.25

High Blood Pressure
In 2010, the Dietary Guidelines Advisory Committee performed a literature review to identify articles examining the effect of dietary patterns on blood pressure in adults. Vegetarian diets were associated with lower systolic blood pressure and lower diastolic blood pressure.26 One randomized crossover trial found that a Japanese diet (low sodium and plant based) significantly reduced systolic blood pressure.27

Mortality
The Dietary Guidelines Advisory Committee also performed a 2010 literature review to determine the effect of plantbased diets on stroke, cardiovascular disease, and total mortality in adults. They found that plant-based diets were associated with a reduced risk of cardiovascular disease and mortality compared with non-plant-based diets.26

The benefit of plant-based diets on mortality may be primarily caused by decreased consumption of red meat.28
Several studies have documented the benefits of avoiding excessive consumption of red meat, which is associated with an increased risk of all-cause mortality and an increased risk of cardiovascular mortality. 29 Low meat intake has been associated with longevity.30

In 2012, Huang et al31 performed a meta-analysis to investigate cardiovascular disease mortality among vegetarians and nonvegetarians. They only included studies that reported relative risks and corresponding 95% confidence intervals. Seven studies with a combined total of 124,706 participants were analyzed. Vegetarians had 29% lower ischemic heart disease mortality than nonvegetarians.31

Health Concerns About
Plant-Based Diets

Protein
Generally, patients on a plant-based diet are not at risk for protein deficiency. Proteins are made up of amino acids, some of which, called essential amino acids, cannot be synthesized by the body and must be obtained from food. Essential amino acids are found in meat, dairy products, and eggs, as well as many plant-based foods, such as quinoa.32 Essential amino acids can also be obtained by eating certain combinations of plantbased foods. Examples include brown rice with beans, and hummus with whole wheat pita. Therefore, a well-balanced, plant-based diet will provide adequate amounts of essential amino acids and prevent protein deficiency.33

Soybeans and foods made from soybeans are good sources of protein and may help lower levels of low-density lipoprotein in the blood34 and reduce the risk of hip fractures35 and some cancers. A study in the Journal of the American Medical Association36 reported that women with breast cancer who regularly consumed soy products had a 32% lower risk of breast cancer recurrence and a 29% decreased risk of death, compared with women who consumed little or no soy.36 An analysis of 14 studies, published in the American Journal of Clinical Nutrition, showed that increased intake of soy resulted in a 26% reduction in prostate cancer risk.37

Because of concerns over the estrogenic nature of soy products, women with a history of breast cancer should discuss soy foods with their oncologists. Also, overly processed, soy-based meat substitutes are often high in isolated soy proteins and other ingredients that may not be as healthy as less processed soy products (ie, tofu, tempeh, and soy milk).

Iron
Plant-based diets contain iron, but the iron in plants has a lower bioavailability than the iron in meat. Plant-based foods that are rich in iron include kidney beans, black beans, soybeans, spinach, raisins, cashews, oatmeal, cabbage, and tomato juice.38 Iron stores may be lower in individuals who follow a plant-based diet and consume little or no animal products. However, the American Dietetic Association states that iron-deficiency anemia is rare even in individuals who follow a plant-based diet.39

Vitamin B12
Vitamin B12 is needed for blood formation and cell division. Vitamin B12 deficiency is a very serious problem and can lead to macrocytic anemia and irreversible nerve damage. Vitamin B12 is produced by bacteria, not plants or animals. Individuals who follow a plant-based diet that includes no animal products may be vulnerable to B12 deficiency40 and need to supplement their diet with vitamin B12 or foods fortified with vitamin B12.41

Calcium and Vitamin D
Calcium intake can be adequate in a well-balanced, carefully planned, plantbased diet. People who do not eat plants that contain high amounts of calcium may be at risk for impaired bone mineralization and fractures. However, studies have shown that fracture risk was similar for vegetarians and nonvegetarians. The key to bone health is adequate calcium intake, which appears to be irrespective of dietary preferences.42 Some significant sources of calcium include tofu, mustard and turnip greens, bok choy, and kale. Spinach and some other plants contain calcium that, although abundant, is bound to oxalate and therefore is poorly absorbed.43

Vitamin D deficiency is common in the general population. Plant-based products such as soy milk and cereal grains may be fortified to provide an adequate source of Vitamin D.44 Supplements are recommended for those who are at risk for low bone mineral density and for those found to be deficient in vitamin D.

Fatty Acids
Essential fatty acids are fatty acidsthat humans must ingest for good health because our bodies do not synthesize them. Only two such essential fatty acids are known: linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid). Three other fatty acids are only conditionally essential: palmitoleic acid (a monounsaturated fatty acid), lauric acid (a saturated fatty acid), and gamma-linolenic acid (an omega-6 fatty acid). Deficiency in essential fatty acids may manifest as skin, hair, and nail abnormalities.45 The fatty acids that vegans are most likely to be deficient in are the omega-3 fats (n-3 fats). Consumptions of the plant version of omega-3 fats, alpha-linolenic acid, are also low in vegans. Adequate intake of n-3 fats is associated with a reduced incidence of heart disease and stroke. Foods that are good sources of n-3 fats should be emphasized. They include ground flax seeds, flax oil, walnuts, and canola oil.46

Conclusion
A healthy, plant-based diet requires planning, reading labels, and discipline. The recommendations for patients who want to follow a plant-based diet may include eating a variety of fruits and vegetables that may include beans, legumes, seeds, nuts, and whole grains and avoiding or limiting animal products, added fats, oils, and refined, processed carbohydrates. The major benefits for patients who decide to start a plant-based diet are the possibility of reducing the number of medications they take to treat a variety of chronic conditions, lower body weight, decreased risk of cancer, and a reduction in their risk of death from ischemic heart disease.

A plant-based diet is not an all-ornothing program, but a way of life that is tailored to each individual. It may be especially beneficial for those with obesity, Type 2 diabetes, high blood pressure, lipid disorders, or cardiovascular disease. The benefits realized will be relative to the level of adherence and the amount of animal products consumed. Strict forms of plant-based diets with little or no animal products may be needed for individuals with inoperable or severe coronary artery disease. Low-sodium, plant-based diets may be prescribed for individuals with high blood pressure or a family history of coronary artery disease or stroke. A patient with obesity and diabetes will benefit from a plant-based diet that includes a moderate amount of fruits and vegetables and minimal low-fat animal products. Severe obesity may require counseling and initial management with a low-calorie diet or very-low-calorie diet and the supervision of a physician’s team. Patients with kidney disease may need a plant-based diet with special restrictions, for example fruits and vegetables that are high in potassium and phosphorus. Finally, patients with thyroid disease will need to be careful when consuming plants that are mild goitrogens, like soy, raw cruciferous vegetables, sweet potatoes, and corn. These patients should be informed that cooking these vegetables inactivates the goitrogens.

Physicians should advocate that it is time to get away from terms like vegan and vegetarian and start talking about eating healthy, whole, plant-based foods (primarily fruits and vegetables) and minimizing consumption of meat, eggs, and dairy products. Physicians should be informed about these concepts so they can teach them to staff and patients.

A registered dietitian should be part of the health care team that designs a plant-based diet for patients with chronic disease, especially if multiple medications are involved. Depending on the underlying conditions, patients with chronic disease who take multiple medications need close monitoring of low blood sugar levels, low blood pressure, or rapid weight loss. If these occur, the physician may need to adjust medications. In some cases, such as the one presented here, the need for certain medications can be eliminated altogether. Although the risk of deficiencies may be low, health care teams need to be aware that a motivated patient on a strict plant-based diet may need monitoring for deficiencies of certain nutrients, as outlined above.

The purpose of this article is to help physicians understand the potential benefits of a plant-based diet, to the end of working together to create a societal shift toward plant-based nutrition. There is at least moderate-quality evidence from the literature that plant-based diets are associated with significant weight loss and a reduced risk of cardiovascular disease and mortality compared with diets that are not plant based. These data suggest that plant-based diets may be a practical solution to prevent and treat chronic diseases.

Further research is needed to find ways to make plant-based diets the new normal for our patients and employees. We cannot cure chronic diseases, but we may be able to prevent and control them by changing how we eat. With education and monitoring for adherence, we can improve health outcomes. Patterns of families and other colleagues who may be reluctant to support the efforts of individuals who are trying to change are a challenge to be overcome. We should invite our colleagues, patients, and their families to a shared decision-making process with the goal of adopting a plant-based diet and a regular exercise program. We should invite health care teams to complete a course on healthy eating and active living. We should encourage staff to be knowledgeable about plant-based nutrition. Finally, we should encourage performance-driven measurable outcomes, which may include:
1. the percentage of physicians who have completed a course on nutrition that includes a discussion of the benefits of a plant-based diet and exercise;
2. the percentage of our hospitals, cafeterias, and physicians’ meeting facilities that serve meals that are consistent with a plant-based diet;
3. the percentage of patients on a physician panel who are obese and who have completed a course on weight management and nutrition that emphasizes a plant-based diet;
and 4. the percentage of patients in a physician panel with high blood pressure, diabetes, high cholesterol, or cardiovascular disease who completed a course on nutrition that emphasizes a plant-based diet.

Too often, physicians ignore the potential benefits of good nutrition and quickly prescribe medications instead of giving patients a chance to correct their disease through healthy eating and active living. If we are to slow down the obesity epidemic and reduce the complications of chronic disease, we must consider changing our culture’s mind-set from “live to eat” to “eat to live.” The future of health care will involve an evolution toward a paradigm where the prevention and treatment of disease is centered, not on a pill or surgical procedure, but on another serving of fruits and vegetables.

Disclosure statement
The author(s) have no conflicts of interest to disclose.

Acknowledgment
Kathleen Louden, ELS, of Louden Health Communications provided editorial assistance.

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Medicine
Let food be thy medicine and medicine be thy food.
— Hippocrates, c 460-370 BCE, ancient Greek physician in the Age of Pericles known as the father of modern medicine

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