While many people are still waiting for swine-flu vaccine to become available in their area, there is a lot they can do in their own kitchens to help fight off disease and build a strong immune system.

    Scientists in the growing field of nutritional immunology are unveiling new evidence of the complex role that nutrition plays in fighting off infectious diseases like influenza. A diet rich in nutrients such as vitamin A, found in colorful fruits and vegetables, and zinc, found in seafood, nuts and whole grains, can provide the critical fuel the body needs to fight off disease, heal injuries, and survive illness when it does strike, experts say.

    Scientists are still studying all the complex ways in which nutrients interact with the immune system. There is still much that they don't know about minerals such as zinc, for instance, including how they are absorbed and all the roles they play in the body. But scientists do know that certain vitamins and minerals can improve the body's ability to fight off infection: Studies in healthy elderly adults, for example, have shown an improved immune response to vaccination and fewer infections after receiving extra doses of vitamin E.

    To create immune cells to fight off a specific infection, the body has to rapidly draw nutrients from the bloodstream, says Anuraj Shankar, a researcher at the Harvard School of Public Health. 'If you don't have an adequate intake of vitamins and minerals, you won't be able to produce the number of immune cells you need, and the immune cells you do produce may be compromised,' Dr. Shankar says. That makes it impossible to mount an effective response to infection, he says.

    Researchers warn that malnourished people may be a breeding ground for more dangerous infectious diseases. Animal studies at the University of North Carolina show that in a host with poor nutrition, viruses mutate in the face of a weak immune response to become more powerful. And once those mutations occur, even well-nourished hosts are susceptible to the newly virulent virus. 'A lot of people may think malnutrition on the other side of the world isn't their problem,' says Melinda A. Beck, a researcher at the University of North Carolina, Chapel Hill. But malnutrition 'is a driving force in emerging infectious diseases that are spreading around the world,' she says.

    The human body doesn't have to be starving to suffer from malnutrition. Studies show that obesity, in addition to its other health risks, may also make people more susceptible to infections like the flu. A diet heavy on processed and fast foods may be low in the vitamins and minerals important for health. And diets that are high in saturated fat appear to actually depress the body's immune response, increasing the risk of infections.

    Dr. Beck says studies of mice show that only 4% of lean animals infected with the flu virus die. That compares with a death rate of between 40% and 60% in obese mice infected with the virus. And after a small study showed that obese people vaccinated for the flu didn't mount a strong immune response, the University of North Carolina is expanding its trials to compare vaccination response rates in lean and obese people.

    When obese people fall ill, 'their immune function may not be strong enough to mount an effective response,' says Donald Hensrud, a Mayo Clinic specialist in preventive and internal medicine and editor-in-chief of 'The Mayo Clinic Diet,' a new book promoting weight loss through a healthy diet that allows unlimited quantities of fruits and vegetables.

    Dr. Hensrud and other experts caution against loading up on supplements to add vitamins and minerals to the diet. While a multivitamin is a good addition to any balanced diet, individual supplements and vitamin pills may not be as well absorbed by the body as nutrients in foods. Some supplements also can have toxic effects in too-high quantities. An excess of zinc, for example, can interfere with absorption of other nutrients, including iron and copper. And too much of the mineral selenium can cause nerve damage and has been linked recently to an increased risk of diabetes.

    Scientists have long known that some vitamins, minerals and other nutrients can play a key role in the immune system by acting as antioxidants. These protect and repair cells from oxidative stress, the damage caused by molecules known as free radicals.

    Nutritional experts generally agree that the best way to get the right balance of nutrients is a balanced diet that includes plenty of fresh fruits and vegetables, lean proteins and dietary fiber.

    Nutrition experts say to boost immunity it is also important to avoid processed foods, and to minimize trans fats and unhealthy saturated fats from animal products and vegetable oils like palm and coconut. Instead, they say, people should eat foods rich in unsaturated fats such as olive oil.

    許多人仍在等著甲型H1N1流感疫苗輪到自己，其實他們在自家廚房也能做很多事，幫助抵抗疾病，建立強壯的免疫系統。

    日漸發展的營養免疫學領域的科學家們正發現新的證據，表明營養在對抗流感等流行疾病方面扮演著復雜的角色。專家說，富含維他命A（色彩鮮艷的水果和蔬菜）和鋅（海鮮、干果和全麥）的餐食能夠為身體提供抵抗疾病、愈合傷口以及患病時存活下來所需的能量。

    科學家們仍在研究營養成份與免疫系統相互作用的復雜方式。礦物質仍有許多地方不為科學家們所知，比如說鋅，包括它們如何被人體吸收，以及扮演何種角色。但科學家們知道，某些維他命和礦物質可以提升人體的抗感染能力：比如，對健康老年人的研究顯示，在增加服用維他命E之后，老人對疫苗的免疫反應增強了，降低了感染。

    哈佛大學公共健康學院（Harvard School of Public Health）研究人員Anuraj Shankar說，為了制造抵抗感染的免疫細胞，人體必須從血液循環系統迅速獲取營養成分。如果不攝入足夠的維他命和礦物質，就無法制造所需數量的免疫細胞，而制造出來的免疫細胞也可能有問題。這樣一來就不可能對感染做出有效的應對。

    研究人員警告說，營養不良者可能產生更危險的傳染病。北卡羅來納大學（University of North Carolina）的動物研究表明，在營養狀況不良的宿主內，面對虛弱免疫反應的病毒會發生變異，變得更為強大。而一旦出現變異，就算是營養狀況良好的宿主也會受到新的惡性病毒影響。北卡羅來納大學研究人員貝克（Melinda A. Beck）說，許多人或許認為地球另一邊的人營養不良不關他們的事，但正是營養不良促使了在全球肆虐的新型傳染疾病的出現。

    人體營養不良并不一定是因為饑餓所致。研究表明，肥胖除了會導致其他健康風險，也可能令人更容易感染流感等傳染疾病。偏重加工食品和快餐食品的飲食可能缺乏對健康十分重要的維他命和礦物質。而飽和脂肪含量高的飲食似乎會抑制人體的免疫反應，增加感染風險。

    貝克說，對老鼠的研究表明，體型較瘦的動物感染流感病毒后死亡率僅為4%.而肥胖的老鼠感染流感病毒后死亡率為40%-60%.一項小規模研究表明，接種了流感疫苗的肥胖者并沒有發生強烈的免疫反應，此后北卡羅來納大學擴大了實驗范圍，比較瘦人和胖人的接種反應率。

    梅約醫院（Mayo Clinic）預防和內科專家韓斯魯德（Donald Hensrud）說，肥胖者一旦生病，其免疫機能可能不足以積聚有效的反應。韓斯魯德是《梅約醫院減肥節食法》（The Mayo Clinic Diet）一書的主編，這本新書提倡通過健康飲食減肥，不限制水果蔬菜的量。

    韓斯魯德和其他專家對過多地靠維他命補充來增加飲食中的維他命和礦物質提出警告。雖然多種維他命劑是對均衡飲食的有益補充，但人體對單獨的補充劑和維他命片劑的吸收情況不如食物中的營養那么好。一些補充劑用量過高還可能導致毒副作用。比如，過量的鋅會妨礙鐵和銅等其他營養成分吸收。而礦物質硒過量會導致神經受損，最近還與糖尿病風險升高聯系起來。

    科學家們早已了解到，維他命、礦物質和其他營養成分可充當抗氧化劑，在免疫系統中扮演重要角色。它們可以保護細胞不受氧化應激影響并予以修復，氧化應激是被稱為自由基的分子導致的損害。

    營養學家普遍認為，攝取均衡營養的最佳途徑是均衡飲食，其中要包括大量新鮮水量和蔬菜、精益蛋白質和膳食纖維。

    營養專家說，要提升免疫力，至關重要的是避免加工食品，盡可能減少攝入動物產品和棕櫚油、椰子油等植物油中所含的反式脂肪和不健康的飽和脂肪。相反，人們應當吃橄欖油等富含不飽和脂肪的食品。