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作者：Nancy A. Melville  
出處：WebMD醫學新聞

　　February 22, 2010 (維吉尼亞州阿靈頓) — 根據發表於「美國預防醫學院年會：2010預防醫學」的研究，每天食用胡桃可以改善第2型糖尿病患的血漿脂質與內皮功能。
　　
　　因為富含多元不飽和脂肪以及單元不飽和脂肪，多種堅果被視為各種飲食中的健康成分，特別是胡桃，富含omega-3脂肪酸。耶魯大學的研究者提出一個理論，添加胡桃可以對糖尿病患的心血管有所幫助。
　　
　　本研究的共同作者、耶魯大學預防研究中心主任David L. Katz醫師向Medscape Public Health Prevention表示，我們知道堅果富含纖維，也含有多種微量營養素、礦物質、維他命B群、鎂等多種特性，讓它們成為對有心血管風險者有幫助的食物。
　　
　　Katz醫師解釋道，我們想瞭解這對於高風險族群如第2型糖尿病成人的血管是否有幫助。
　　
　　這個隨機控制交叉試驗包括了患有第2型糖尿病、平均年紀58歲的24名研究對象(14名女性與10名男性)，這些人被隨機指派接受每天含有56g胡桃的Ad libitum diet (自由飲食組)、或者不含有胡桃的自由飲食組。
　　
　　該研究在各8週的治療期之間，包括了一個為期8週的廓清期，在每一期的前後，研究對象接受內皮功能檢測與評估心血管生物標記。
　　
　　該研究的初級結果是8週之後血流介導擴張(flow-mediated dilatation，FMD)的變化，次級終點包括血漿脂質、糖化血色素(HbA1c)、空腹血糖值、胰島素敏感性、人體測量等的改變。
　　
　　相較於飲食中不含胡桃者，食用富含胡桃飲食者的FMD有顯著改善(FMD，2.2%± 1.7 % vs 1.2%± 1.6 %；P= .04)。
　　
　　雖然食用胡桃者的總膽固醇(–9.7± 14.5mg/dL；P< .01)、低密度脂蛋白(LDL)膽固醇(–7.7± 10.0 mg/dL；P< .01)比研究開始時降低，但是，與飲食中不含胡桃者相比(總膽固醇 –9.7± 14.5 vs –4.5± 23.0；P=.38；LDL膽固醇–7.7± 10.0 vs –7.8± 20.6；P= .97)，降低幅度並不顯著。
　　
　　該研究在人體測量、HbA1c、空腹血糖值、胰島素敏感性等方面，也未發現這兩種飲食類型有任何顯著差異。
　　
　　不過，Katz醫師表示，內皮功能方面的發現是關鍵。
　　
　　他表示，在我們次級結果測量的各種其他心臟風險因素方面，與安慰劑相比的確沒有顯著改善，但是，電影《魔戒》中的「掌控全局的王者之戒」給了我一個靈感：聚焦在內皮功能。
　　
　　這給予我一個想法，就是血管如何感覺到流經其中的所有東西，你可以測量任何你認為的在血管中流動的所有東西，例如LDL膽固醇、三酸甘油脂、壓力荷爾蒙，或者，實際上只需要問問血管：「對於流過的東西，你今天的感覺如何？」
　　
　　本研究中的血管可能會回答：「在我們每天被餵食胡桃之後，我們感覺好多了」。
　　
　　該研究也評估了補充胡桃時每天產生的365大卡是否會引起這群已經有可能肥胖的病患其體重增加，結果顯示，食用胡桃者的體重並未顯著增加。
　　
　　Katz醫師解釋，如果將有營養的食物加到飲食中，有時候這個食物的好處會因為造成體重上升而被抵銷，對糖尿病患而言，顯然地，最不想要的事情就是體重增加。但是，我們的研究認為，你可以在飲食中加富含營養的食品，特別是，如果它可以像堅果一樣的話。
　　
　　Katz醫師表示，雖然該研究聚焦在糖尿病，但他的團隊更希望可以證明胡桃對健康者也有幫助。
　　
　　他表示，為了證明某些東西有用，你通常得先從某些故障的東西著手且證明你可以修復它，所以，我們先針對糖尿病，之後是糖尿病前期、然後是糖尿病前期的前期(pre-prediabetes)，最後，希望我們可以提出令人信服的論述，證明這個可以加到每個人的飲食中。
　　
　　我一直認為，為了達到預防優先，我們必須回過頭來研究，而我希望讓健康的人保持健康，我是個照顧病患的醫師，但是，我寧可人們不要生病。
　　
　　加州大學聖地牙哥分校全球健康小組主任、流行病學副教授Wael Al-Delaimy博士表示，杏仁已經顯示有重要助益，糖尿病患或許可以從綜合堅果獲得更佳的幫助。
　　
　　他表示，吃各種堅果是健康的，且應被視為健康生活型態的一部份，因為每種堅果各有獨特的成分，也就是說，胡桃和杏仁因為各自所含的脂肪類型而各有重要的幫助。
　　
　　他指出，杏仁也顯示出對於糖尿病有獨特的幫助。
　　
　　胡桃中最常見的Omega-3脂肪酸對於神經發育和腦部很好，心臟也是，但是，有些研究認為，杏仁有特定的控糖性質。
　　
　　Al-Delaimy博士指出，胡桃的研究並未顯示任何類似的助益。
　　
　　他指出，該研究中，胡桃的劑量是每天需要量的兩倍，但是它依舊無法控制研究對象的葡萄糖相關測量。
　　
　　Katz醫師表示同意，杏仁富含營養且可能也有幫助。在整體營養品質1-100分的NuVal營養評分量表中，82分的胡桃以及79分的杏仁都是營養明星。
　　
　　同時，Katz醫師和他的團隊朝向下一步進行：評估胡桃對於糖尿病前期患者的幫助。
　　
　　我們只是接受資金研究更多糖尿病前期患者，本著將食品當作藥品的這種理念，那麼，問題在於：「誰應該吃這種藥品？」，我們不認為只有糖尿病患而已。
　　
　　Katz醫師的實驗室部份資金來自喬治亞州亞特蘭大疾病控制預防中心，該研究接受加州胡桃委員會的資金， Katz醫師和Al-Delaimy博士皆宣告沒有相關財務關係。
　　
　　美國預防醫學院(AAPM)第26屆年會：壁報摘要212645，發表於2010年2月19日。


Walnuts Shown to Improve Endothelial Function in Diabetics

By Nancy A. Melville
Medscape Medical News

February 22, 2010 (Crystal City, Virginia) — The daily consumption of walnuts has the potential to improve endothelium function and plasma lipids in patients with type?2 diabetes, according to a study presented here at Preventive Medicine 2010: the Annual Meeting of the American College of Preventive Medicine.

With a high polyunsaturated and monounsaturated fat content, many types of nuts have gained favor as a healthy addition to any diet, and walnuts, in particular, have a high level of omega-3 fatty acids. Researchers at Yale University in New Haven, Connecticut, theorized that the addition of walnuts could provide cardiovascular benefits to diabetics.

"We know nuts are rich in fiber, and have a variety of micronutrients, minerals, B?vitamins, magnesium, and a number of properties that make them a likely candidate for benefits in people with cardiovascular risk," David L. Katz, MD, a coauthor on the study and director of the Yale University Prevention Research Center, told Medscape Public Health Prevention.

"We asked if this could prove a vascular benefit in an at-risk population — adults with type?2 diabetes," Dr. Katz explained.

The randomized controlled crossover trial involved 24 subjects (14 women and 10 men) with type?2 diabetes with a mean age of 58 years. The subjects were randomly assigned to receive an ad?libitum diet enriched with 56?g of walnuts per day or an ad?libitum diet without walnut supplementation.

The study involved an 8-week washout period between each 8-week treatment phase. Before and after each phase, participants underwent endothelial function testing and assessment of cardiovascular biomarkers.

The primary outcome measure for the study was a change in flow-mediated dilatation (FMD) after 8 weeks, and secondary outcome measures included changes in plasma lipids, glycated hemoglobin (HbA1c), fasting glucose, insulin sensitivity, and anthropometric measures.

There was a significant improvement in FMD among the participants consuming the walnut-enriched diet, compared with those not consuming diets with walnuts (FMD, 2.2%?± 1.7 % vs 1.2%?± 1.6 %; P?= .04).

Although the subjects consuming walnuts showed reductions from baseline values in total cholesterol (–9.7?± 14.5?mg/dL; P?< .01) and low-density lipoprotein (LDL) cholesterol (–7.7?± 10.0?mg/dL; P?< .01), the reductions were not significant compared with those on the diet without walnuts (total cholesterol, –9.7?± 14.5 vs –4.5?± 23.0; P? .38; LDL cholesterol,?–7.7?± 10.0 vs –7.8?± 20.6; P?= .97).

The study also did not find any significant differences in anthropometric measures, HbA1c, fasting blood glucose, or insulin sensitivity between the 2 diets.

However, Dr. Katz said, the endothelial function findings were key.

"We did not see significant improvement compared with placebo in a variety of the other cardiac risk factors we measured as secondary outcomes, but when it comes to endothelial function, I'm reminded of The Lord of the Rings. It's the 1 ring to rule them all," he said.

"What it tells us is how the blood vessels are feeling in light of everything that is flowing by. You can measure everything you can think of that is flowing by, such as LDL cholesterol, triglycerides, or stress hormones, or you can simply ask the blood vessels, in essence: 'Given everything that is floating by, how are you feeling today?'?"

"And the blood vessels in this study said, 'we feel better after we've been fed walnuts daily.'"

The study also evaluated whether the supplementation of walnuts, representing about 365 calories per day, would cause weight gain in a patient population that is already prone to obesity. The results showed no significant weight gain among subjects receiving walnut supplementation.

"If you're adding a nutritious food to the diet, the benefits of the food might sometimes be offset if weight gain occurs, and obviously, with diabetics, the last thing you want to do is cause weight gain," Dr. Katz explained. "But our study suggests you can make room for a highly nutritious food in your diet, particularly if it tends to fill you up, as nuts do."

Although the study focused on diabetics, Dr. Katz said his team has the more ambitious goal of showing the benefits of walnuts in healthy individuals.

"To prove something works, you often have to begin with something that is broken and show that you can fix it," he said. "So we're working with diabetes first, then prediabetes, then pre-prediabetes, and then hopefully we can make the convincing argument that this should be incorporated in everyone's diet."

"I've long held the view that in order to peddle prevention, we have to work backward, and my interest is keeping healthy people healthy. I am a doctor and I take care of sick people, but I'd prefer people don't get sick in the first place."

Almonds have also shown important benefits, and diabetics may better benefit from a mix of nuts, said Wael Al-Delaimy, MD, PhD, associate professor of epidemiology and chief of the Division of Global Health at the University of California, San Diego.

"A combination of different nuts is always healthy and should be recommended as part of a healthy lifestyle, since each nut has certain unique components," he said. "That being said, walnuts and almonds do stand out with significant benefits because of the type of fats they contain."

Almonds, too, appear to have their own unique benefits for diabetes, he added.

"Omega-3 fatty acids that are mostly in walnuts are very good for nerve development and the brain, and also the heart, but some research suggests that almonds have specific sugar-control qualities."

Dr. Al-Delaimy noted that the walnut study did not show any similar benefits.

"The dose of the walnuts in this study is double the daily required value, yet it still did not control the glucose-related measures in participants," he pointed out.

Dr. Katz concurred that almonds are highly nutritious and likely offer benefits as well. "On the NuVal scale of overall nutritional quality from 1 to 100, both walnuts (at 82) and almonds (at 79) stand out as nutrition superstars."

In the meantime. Dr. Katz and his team are moving ahead to the next step of evaluating the benefit of walnuts in prediabetics.

"We just received funding to study a larger cohort of prediabetics as we pursue this notion of food as medicine. Then the question is, 'Who should take this medicine?', and we don't think the answer is just diabetics."

Dr. Katz's lab is funded in part by the Centers for Disease Control and Prevention in Atlanta, Georgia. The study received funding from the California Walnut Commission. Dr. Katz and Dr Al-Delaimy have disclosed no relevant financial relationships.

American Academy of Pain Medicine (AAPM) 26th Annual Meeting: Poster abstract?212645. Presented February?19, 2010.