原创性研究与贡献 2013 春天
特别报导
给医生的营养最新讯息：植物为主的饮食
作者:Philip J Tuso, MD; Mohamed H Ismail, MD; Benjamin P Ha, MD; Carole Bartolotto, Ma, RD
译者:寂光寺
DOI: dx.doi.org/10.7812/TPP/12-085
摘要
本文的目的是介绍给医生最新的以植物为主的饮食。尽管医疗照护成本不断升高的问题引起全国注意，人们不健康的生活方式导致肥胖，糖尿病和心血管疾病等问题持续在蔓延，医生们因此寻找真正有效帮助病人采取较健康的生活方式。而最有助于健康的饮食习惯是以植物性食物为主，我们定义为「养生法」，提倡天然植物性食物，不鼓励肉类，奶制品和鸡蛋以及所有经过精致加工的食品。在此我们提出了一个案例来说明这种饮食习惯有助身体健康。 研究显示，植物为主的饮食能有效，且低风险的降低体脂比(BMI：体重kg/身高2m)、血压、糖化血色素和胆固醇。这种饮食方式也可以减少治疗慢性疾病所需的药物数量，和降低缺血性心脏病的死亡率。医生应考虑建议所有的病人以植物性食物为主的饮食方式，特别是患有高血压、糖尿病、心血管疾病或肥胖的病人。
引言
在HBO的纪录片《 The weight of the Nation 》﹙暂译：全民的重量﹚中提到，如果在美国你「顺其自然」地跟随大众饮食趋势，你最终会变得肥胖1。2011年，Witters威特尔斯报导，在美国一些地区人民的肥胖率是39％，且以每年5％的速度增长2。肥胖、糖尿病、高血压和心血管疾病的风险，及随之而来的并发症（如行为上的健康和生活品质的问题）往往与生活方式息息相关，尤其是饮食的选择3。过去几十年来为减少慢性疾病发生而提倡的所有饮食方式中，最好且也许最普遍的可能就是以植物性饮食为主的方式。
尽管已经有证据证明强壮的身体倾向来自于植物为主的饮食方式，也有研究显示一般大众很乐意尝试植物性饮食4，但许多医生仍不强调以植物性饮食作为治疗慢性疾病的首要方式。这可能是因为缺乏有关这些饮食的正确认知或缺乏这方面的教育学习资源。
《国家膳食指南》中针对活跃的生活和健康饮食(可参考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（非淀粉类蔬菜和水果）、四分之一的全谷类或未加工的淀粉类食物，和四分之一的瘦肉蛋白所组成。
这篇文章的目的，是审视支持以植物为主的饮食实例文献，并提供介绍此饮食方式的指南。我们先从一个案例研究开始，最后会做结论并附上参考文献。
案例研究
一位63岁有高血压病史的男子跟医生抱怨他的疲劳、恶心、肌肉痉挛。他的随机血糖测试的结果为524毫克/分升，和糖化血色素是11.1％。经诊断为2型糖尿病。他的总胆固醇为283毫克/分升、血压是132/66 毫米汞柱、和体脂比（BMI）为25公斤/平方米。他每天服用lisinopril赖诺普利(治疗高血压的药)40毫克;hydrochlo-rothiazide氢氯塞治锭 (治疗高血压的药)每天50毫克;amlodipine脉优锭(降高血压，心绞痛的药)每天5毫克,和atorvastatin阿托伐他汀(降胆固醇药)每天20毫克。他的处方为metformin迈胰妥膜衣锭 (治糖尿病的药)1000毫克每天两次,glipizide泌乐得锭(治糖尿病的药)每天5毫克以及睡前服用10个单位赫氏中性鱼精蛋白胰岛素(降血糖的药)。他的医生也规定他要以低钠盐，植物为主的饮食—每天食用不含所有动物产品、精制糖和少许的面包、白饭、马铃薯和玉米片。可以吃无限量不含淀粉的蔬菜和豆类及每天最多2盎司的坚果类。他还被要求开始每天两次15分钟的运动。
此患者每月回诊。在第16周时，从生物统计学上来看有显著改善结果：他完全停用脉优锭、氢氯塞治锭、泌乐得锭、赫氏中性鱼精蛋白胰岛素。追踪血压为低于125/60毫米汞柱，糖化血色素进步到6.3％，并且总胆固醇进步到138毫克/分升。赖诺普利逐渐降低至每天5毫克而且他的糖尿病只以每天两次 1000毫克的迈胰妥膜衣锭来控制。
植物为主的饮食定义
这个引人注目的例子，显示以植物为主的饮食可以从生物统计学成果如血压、糖尿病和脂质分布看出其成效。糖化血色素三个月内从11.1％降低到6.3％，比预期单一使用迈胰妥膜衣锭6的治疗或日常运动7 的成效还要来的更好。也观察到在临床实验中鲜少遇到超过4个月期间使用少量药物的，血压有所改善，并且很可能与低钠饮食和避免红肉有所关连。由于病人不是肥胖，在节食上也没有明显降低体重，这戏剧性的改善似乎是与他的新饮食的品质有关。
健康的植物性饮食目的是大量增加营养丰富的植物性食物，同时尽量减少加工食品，油和动物性食物（包括乳制品和蛋）。鼓励多吃蔬菜（熟或生）、水果、豆类、豌豆、扁豆、大豆、种子和坚果(少量）及一般的低脂脂肪8,9 。该领域的主要支持者对最佳的植物性饮食应包含哪些持不同的意见 。Ornish 欧尼斯等人建议使用少量的动物性产品如蛋白和脱脂牛奶以便战胜疾病10,11。
Esselstyn服务于克利夫兰诊所健康机构，指导心血管预防和逆转程序，他建议完全避免所有的动物性产品以及大豆和坚果，特别是如果患者有严重冠状动脉疾病12。尽管有这些小差异，还是有证据表明广义的以植物为主的饮食对身体有显著的健康益处。特别指出的是，「植物为主」 这个术语有时可以互换为「素食」或「纯素」 。基于道德或宗教(不是基于增进身体健康)的理由而采用素食或全素饮食，并不一定保证能指向健康。 因此，重要的是要知道相关饮食的具体定义及确定病人的饮食细节，而不是单纯假设它是如何的健康。以下是一个典型的限制动物产品饮食的简要总结。关键的区别是，大多数的饮食是以其不包含的食物来定义，然而植物为主的饮食则是以它包含的内容物来定义。
Vegan (or total vegetarian) 纯素（或完全素食）：不包括所有动物产品，特别是肉类、海鲜、家禽、蛋和奶制品。不需要食用天然食品或限制脂肪或精制糖。
Raw food, vegan 生食，纯素：与素食主义有相同的食物排除类别以及排除所有烹煮温度超过华氏118°F的熟食品(约摄氏47.7°C)。
Lacto-vegetarians奶素 : 不包括蛋、肉、海鲜、家禽、包括牛奶产品。
Ovo-vegetarian蛋素：不包括肉类、海鲜、家禽和奶制品，包括鸡蛋。
Lacto-ovo vegetarian奶蛋素：不包括肉类、海鲜、家禽，包括鸡蛋和奶制品。
Mediterranean 地中海式：类似于以天然食品、植物为主的饮食习惯，但允许少量鸡肉、奶制品、蛋，和每月一次或两次的红肉。鼓励食用鱼和橄榄油。没有限制脂肪。
Whole-foods, plant-based, low-fat天然食品、植物为主、低脂肪： 鼓励天然的植物性食物，尤其是蔬菜、水果、豆类和种籽和坚果 (少量)。为了最大的健康效益，这样的饮食限制动物产品。总量脂肪一般是限制的。
植物为主的饮食之好处
我们饮食的目的应该是要改善健康。在本段落中，我们将回顾文献的关键内容，证明以植物为主的饮食之好处。我们会审视包括现有的研究，涵盖纯素、素食和地中海式饮食。
肥胖
2006年，审查87篇研究报告后，作者Berkow和 Barnard 13在《营养评价》 中提出纯素或素食的饮食对降低体重是非常有效的。他们还发现该素食人群的心脏病，高血压、糖尿病和肥胖发病率较低。另外，他们的审查也建议，素食者的体重下降不是依赖于运动，而且每周大约是下降一磅的比率(约0.45公斤) 。作者进一步说明纯素饮食饭后较能燃烧更多卡路里，相对来说，因为食物被储存为脂肪13，非素食饮食可能导致较少的热量被然烧。
Farmer等人14建议相较于其他含肉饮食，素食饮食可能较有助于管理体重，并且可能更有营养。在他们的研究中发现，素食者比食肉者更苗条。也发现素食者摄取更多的镁、钾、铁、硫胺素、核黄素、叶酸和维他命及较低的脂肪总量。作者的结论是：素食饮食不但营养高且可推荐用于体重管理，并且不影响饮食品质14。
2009年，Wang 和Beysoun15分析1999-2004年卫生与营养调查的全国代表性的数据。研究的目的是分析肉类消费和肥胖之间的关连。用线性和物流回归分析，他们发现，肉类消费和肥胖呈现正相关15。
欧洲前瞻性调查癌症和营养的牛津分部，针对在英国超过五年时间的肉食、鱼食、素食和纯素食的男性和女性，评估其体重和BMI变化。五年的研究中，这些人当中饮食改变成少量的动物性食物的人，每年增加的体重是最低的。该研究还报导了在年龄调整体重指数有显著的差异 ，肉食者具有最高的BMI，而素食主义者则是最低的16。基督复活安息日会健康研究也有类似的结果报告17。
根据Sabaté and Wien 18，流行病学研究表明，不论是成年人及儿童，素食饮食与降低BMI、降低肥胖趋势是相关连的。关于成人素食饮食研究的整合分析估计，体重减少的差异，男性为7.6公斤，女性为3.3公斤，BMI因此降低2个指数。同样地，与非素食者相较，素食儿童比较结实，而且他们的BMI差异在青春期是越大的。探索超重风险和食物类别及饮食模式的研究表明，植物为主的饮食似乎是预防儿童肥胖的明智方法。以植物为主的饮食是低能量密度和高复合糖、纤维以及水，可以增加饱足感和静息能量的消耗18。此研究结论是以植物为主的饮食模式应该是对健康最好的。
糖尿病
比起非以植物为主的饮食，以植物为主的饮食之益处是预防及控制糖尿病。基督复活安息日会健康研究发现，素食者得糖尿病的风险仅是非素食者的一半不到19。2008年，Vang等人20 报导，非素食者比素食者有74％的可能发展为糖尿病超过17年的时间。2009年，涉及超过60,000名男性和女性的一个研究发现，糖尿病中的个人的患病率，纯素饮食为2.9％，非素食者则为7.6％17。低脂肪、以植物为主的饮食并且无肉或少肉饮食可能有助于预防和治疗糖尿病，大概是因其改善胰岛素敏感性和降低胰岛素抵抗。
Barnard等人21 在2006年报告一项随机临床试验，关于采用低脂纯素饮食和根据美国糖尿病组织的饮食指导的比较结果。采用低脂纯素饮食的人其糖化血色素减少 1.23点，而遵循美国糖尿病组织的饮食指导的人则是0.38点。此外，43％的低脂纯素饮食的人能减少用药，而遵循美国糖尿病组织的饮食指导的人则是26％18 。
心脏疾病
在The Lifestyle Heart Trial 生活方式及心脏试验的研究中，Ornish10发现82％患有心脏疾病且依据他的生活指导安排的病人，其动脉粥状硬化有某种程度的复原。甚至对严重的冠状动脉粥状硬化的复原只要一年的时间，全面改变生活方式似乎是促进因素。他的植物为主的食物疗法中，热量的10％来自脂肪，15％至20％来自蛋白质，70％至75％来自碳水化合物，胆固醇被限制在每天5毫克。有趣的是，与对照组的53％有动脉粥样硬化的进展。经过5 年，狭窄症的实验组从37.8％下降至34.7％ (7.9％相对改善）。对照组经历了狭窄症的进展从46.1％到57.9％（27.7％相对恶化）。低密度脂蛋白在1年时已减少40％，而且5年后保持在20% 少于基准线。这些降低情况类似于降脂药物的效果10,11。
里昂饮食心脏研究一个前瞻、随机、二级预防化的试验中，de Lorgeril发现干预组（在第27个月）有73％减少冠心病事件并且在所有原因的死亡率降低了70％。干预组的地中海式饮食中包含比肉还更多的植物性食物，蔬菜、水果、鱼。牛油和奶油换成了菜籽油的人造奶油。菜籽油和橄榄油是唯一建议的脂肪来源22。
1998年，有一份协同分析采用 了5篇前瞻性研究的原始数据进行审查，并被发表在《公共健康营养杂志》上。 其中比较了素食者和非素食者之特异的缺血性心脏疾病死亡率的比例。素食者在缺血性心脏疾病死亡率相对非素食者减少24％23。缺血性心脏病的风险较低可能与摄取少肉的人胆固醇较低有关连24。
虽然素食饮食与几种慢性疾病有低风险的关连，但不同类型的素食者在健康上也可能不一定有相同的效果。关键是要吃得健康，而不是只是纯素或素食饮食就够了25。
高血压
2010年，美国饮食指标指导委员会进行了文献审查，为了研究文献资料中关于饮食模式对成人血压的影响。证实素食饮食和降低血压有相关26。一个随机交叉试验发现了一种日本人的饮食（低钠和以植物为主） 显著降低收缩压27。
死亡
美国饮食指标指导委员会进行了2010年的文献审查，确定了植物为主的饮食在中风、心血管病和成人的总死亡率的影响。他们发现，植物为主的饮食比非植物为主的饮食能降低心脏血管疾病和死亡率26。
植物为主的饮食降低死亡率的最主要原因是减少食用红肉28。几项研究已经证明了避免食用红肉的好处，红肉具有增加所有死亡及心血管疾病死亡率的关联性29。摄取少量肉类比较能长寿一直都有相关30。
2012年，Huang等人31，以素食者和非素食者之间心血管疾病的死亡率执行整合分析研究。他们只取相对风险及符合95％的信赖区间的研究报告。7篇研究报告共有124,706参加者进行了分析。 显示素食者相对非素食者有低于29％的缺血性心脏疾病的死亡率31。
植物为主的饮食之健康关注问题
蛋白质
一般来说，以植物为主的饮食的患者并没有缺乏蛋白质的风险。蛋白质是由氨基酸组成的，其中一些被称为必需氨基酸， 是人体不能自行合成， 必须从食物中获得。而必需氨基酸存在于肉类、乳制品和蛋以及许多植物性食物，如藜麦32。必需氨基酸也可以从摄取某些组合的植物性食物而得到。 例如，糙米和豆类、鹰嘴豆泥搭配全麦皮塔。因此，均衡的植物为主的饮食可以提供足够的必需氨基酸和防止蛋白质缺乏症33。
大豆和大豆制成的食品是蛋白质的良好来源，并且可以帮助降低在血液中的低密度脂蛋白34，并减少臀部骨折的风险35 和一些癌症。
《美国医疗协会杂志 》的一项研究36报导，患有乳腺癌的妇女经常食用大豆相较于很少或不食用大豆的妇女降低32％乳腺癌复发的风险，并降低29％的死亡风险36。一份发表在《美国临床营养学杂志》的14项研究报告的分析，显示增加大豆摄取剪少了26％前列腺癌的风险37。
由于豆制品有雌激素，有乳腺癌病史的女性应该与其肿瘤科医师讨论大豆食品摄取量。此外，过度加工大豆做的肉类替代品往往高度分离大豆蛋白质和其他成分，这可能不如少量加工的大豆产品来得健康（如豆腐、天贝、豆浆）。
铁
植物为主的饮食含铁，但铁在植物中相较肉类来说属较低的生物利用度。植物性食物中含丰富铁质包括四季豆、黑豆、黄豆、菠菜、葡萄干、腰果、燕麦片，高丽菜和番茄汁38。对遵循植物为主的饮食并摄取很少或不摄取动物产品的人来说，铁的储存可能比较低。然而，美国饮食协会指出对遵循植物为主的饮食的人来说，缺铁性贫血却是罕见的39。
维他命B12
血液的生成和细胞分裂是需要维他命B12 的。 缺乏维他命B12 是一个很严重的问题，可以导致巨红细胞性贫血和不可逆转的神经损伤。维他命B12 是由细菌制造的，而不是植物或动物。遵循植物为主且不食用任何动物产品的人可能容易缺乏维他命B1240 ，他们必须补充含有维他命B12或者强化维他命B12的食物41。
钙和维他命D
在均衡、精心策划、植物为主的饮食中钙是足够的。不吃含有高钙的植物的人可能处于骨质矿化和骨折的危险之中。 然而，研究表明，骨折的风险不论对素食者和非素食者来说是差不多的。促进骨骼健康的关键是摄入足够的钙，这似乎与饮食喜好不相干42。 一些重要的钙质来源包括豆腐，芥末和芜菁块根叶 ，白菜和甘蓝。菠菜和其他一些含有钙的植物，虽然丰富，但势必会含草酸盐，因此，很难被身体吸收43。
一般人缺乏维他命D是常见的。可以加强植物为主的产品如豆浆和麦片，以提供足够的维他命D来源44。有骨质矿化风险的人及被发现缺乏维他命D的人，建议服用补给品。
脂肪酸
人类身体健康必须摄取必需脂肪酸，因为我们的身体没有合成脂肪酸。只有两种必需脂肪酸是已知的： 亚油酸 ( omega-6 脂肪酸)和α-亚麻酸 (omega-3 脂肪酸)。 其他三个脂肪酸只是条件式的必需： 棕榈油酸 (单元不饱和脂肪酸) ，十二烷酸（饱和脂肪酸）， 和γ-亚麻酸 ( omega-6 脂肪酸)。缺乏必需脂肪酸可能会使皮肤，头发，指甲的看起来异常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-亚麻酸的摄取。充足摄入n-3脂肪酸能降低心脏疾病及中风的发生率。其实包括亚麻籽，亚麻籽油，核桃，和菜籽油46 都是n-3脂肪良好来源的食物。。
结论
一个健康的、植物为主的饮食要求也须妥善规划，相关阅读标签和遵守纪律。可以推荐想要遵循植物为主的饮食的患者食用各种水果和蔬菜，包括大豆、豆类、种子、坚果和粗粮，并且避免或限制动物性食品、补充脂肪、油和精制且加工的碳水化合物。患者决定开始以植物性为主的饮食后最大好处就是减少以药物治疗各种慢性疾病、降低体重、降低患癌症 的风险，和降低缺血性心脏疾病的死亡风险。
植物为主的饮食不是一个孤注一掷的计划，而是针对每一个人订做的一种生活方式，对肥胖、2型糖尿病、高血压、脂质异常或心血管疾病的人来说也许特别有益。越能够坚持持之以恒就越能体会到减少动物产品消费的实际好处。不能手术或严重的冠状动脉疾病的人最好能实行严格的植物为主、少量或完全没有动物产品的饮食对有高血压或冠状动脉疾病或中风的家族病史的人可开以低钠盐、植物为主的饮食处方。有肥胖和糖尿病的患者也能从适量的水果和蔬菜及最低的低脂肪动物性产品这类以植物为主的饮食中受益。重度肥胖可能需要咨询及低热量饮食或极低热量饮食的初期管理和医生团队的监督。肾病患者可能需要植物为主的饮食并且有其特殊的限制，例如要注意含量高的钾和磷的水果和蔬菜。最后，甲状腺疾病患者需要小心食用轻微的致甲状腺肿素的植物，如大豆、生的十字花科蔬菜，地瓜和玉米。这些患者应该被告知要烹调这些蔬菜能致甲状腺肿素失活。
医生们应该提倡，是时候该摆脱只以术语如纯素和素食来看待饮食习惯 ，并多建议健康、天然、植物性食物为主的饮食习惯（主要是水果和蔬菜）和减少到最低量的肉类、鸡蛋和奶制品。医师本身应该先了解这些概念，则可以教导其他工作人员和病人。
应该将合格的营养师列入医护团队中，职责是为慢性疾病患者设计植物为主的饮食，而对于服用多种药物的慢性疾病患者，需要密切监测是否低血糖值、低血压或急速体重下降。如果出现这些情况，医生可能需要调整药物。除此以外，如这里所展示的，对某些药物的需求是可以完全消除的。虽然失误风险可能较低，医护团队仍需要知道，对于执行严谨的植物为主饮食的病人，还是可能需要监测某些营养物不足之处，如上文所述。
本文的目的是帮助医生了解以植物为主的饮食之潜在利益，以期最终能共同创造以植物为主的营养为基础的饮食习惯之社会转变。至少从文献中适度质量的证据，及与非以植物为主的饮食相比较，植物为主的饮食显著的与体重下降及心血管疾病和死亡率的风险降低有关连。这些数据表明植物为主的饮食可能是一个预防和治疗慢性疾病实用的解决方法。
为了使我们的患者和医护团队将以植物为主的饮食成为新常态，需要更进一步研究，以找到方法。我们就算不能治愈慢性疾病，但可能能够借由改变我们的饮食去预防和控制它们。 随着不断教育并持续监测，我们可以改善健康结果。 至于不乐意支持他人改变的家庭和其他同事，也是个需要去克服的挑战。
为采纳植物为主的饮食和有规律的运动计划之目标， 我们应该邀请我们的同事，患者及家属共享决策过程。 我们应该邀请健康服务团队来完成一个健康饮食和积极生活的课程。也要鼓励人员熟知以植物为主的食物营养。最后，我们应该鼓励以注重绩效为主的评量，可以包括：
1.医生完成营养学课程的比例，包括讨论植物为主的饮食和运动的好处;
2.医院，餐厅和医师会议设施，其提供之餐点应与「以植物为主的饮食」理念一致的比例;
3.肥胖患者在医师小组里完成针对植物为主的饮食之体重管理和营养学的比例;
4.高血压、糖尿病、高血脂或心血管疾病患者在医师小组里完成针对植物为主的饮食之营养学的比例。
很多时候，医生忽略了良好的营养之潜在益处，只是迅速给予处方，而不是透过健康的饮食和积极的生活让患者有机会改善自己的疾病。如果我们要减缓肥胖流行和减少慢性并发症疾病，我们必须考虑改变我们的文化思维方式，从「活着是为了吃」到「吃是为了活着」。未来的医疗保健演变为以预防和治疗疾病为中心，不是在药物提供或手术操作上，而是在水果和蔬菜上。
公开声明
作者（们）完全没有利益涉入及牵扯。
感谢
Kathleen Louden, ELS, of Louden Health 提供了编辑援助。
参考文献请参照以下原文版
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