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.

    许多人仍在等着甲型H1N1流感疫苗轮到自己，其实他们在自家厨房也能做很多事，帮助抵抗疾病，建立强壮的免疫系统。

    日渐发展的营养免疫学领域的科学家们正发现新的证据，表明营养在对抗流感等流行疾病方面扮演着复杂的角色。专家说，富含维他命A（色彩鲜艳的水果和蔬菜）和锌（海鲜、干果和全麦）的餐食能够为身体提供抵抗疾病、愈合伤口以及患病时存活下来所需的能量。

    科学家们仍在研究营养成份与免疫系统相互作用的复杂方式。矿物质仍有许多地方不为科学家们所知，比如说锌，包括它们如何被人体吸收，以及扮演何种角色。但科学家们知道，某些维他命和矿物质可以提升人体的抗感染能力：比如，对健康老年人的研究显示，在增加服用维他命E之后，老人对疫苗的免疫反应增强了，降低了感染。

    哈佛大学公共健康学院（Harvard School of Public Health）研究人员Anuraj Shankar说，为了制造抵抗感染的免疫细胞，人体必须从血液循环系统迅速获取营养成分。如果不摄入足够的维他命和矿物质，就无法制造所需数量的免疫细胞，而制造出来的免疫细胞也可能有问题。这样一来就不可能对感染做出有效的应对。

    研究人员警告说，营养不良者可能产生更危险的传染病。北卡罗来纳大学（University of North Carolina）的动物研究表明，在营养状况不良的宿主内，面对虚弱免疫反应的病毒会发生变异，变得更为强大。而一旦出现变异，就算是营养状况良好的宿主也会受到新的恶性病毒影响。北卡罗来纳大学研究人员贝克（Melinda A. Beck）说，许多人或许认为地球另一边的人营养不良不关他们的事，但正是营养不良促使了在全球肆虐的新型传染疾病的出现。

    人体营养不良并不一定是因为饥饿所致。研究表明，肥胖除了会导致其他健康风险，也可能令人更容易感染流感等传染疾病。偏重加工食品和快餐食品的饮食可能缺乏对健康十分重要的维他命和矿物质。而饱和脂肪含量高的饮食似乎会抑制人体的免疫反应，增加感染风险。

    贝克说，对老鼠的研究表明，体型较瘦的动物感染流感病毒后死亡率仅为4%.而肥胖的老鼠感染流感病毒后死亡率为40%-60%.一项小规模研究表明，接种了流感疫苗的肥胖者并没有发生强烈的免疫反应，此后北卡罗来纳大学扩大了实验范围，比较瘦人和胖人的接种反应率。

    梅约医院（Mayo Clinic）预防和内科专家韩斯鲁德（Donald Hensrud）说，肥胖者一旦生病，其免疫机能可能不足以积聚有效的反应。韩斯鲁德是《梅约医院减肥节食法》（The Mayo Clinic Diet）一书的主编，这本新书提倡通过健康饮食减肥，不限制水果蔬菜的量。

    韩斯鲁德和其他专家对过多地靠维他命补充来增加饮食中的维他命和矿物质提出警告。虽然多种维他命剂是对均衡饮食的有益补充，但人体对单独的补充剂和维他命片剂的吸收情况不如食物中的营养那么好。一些补充剂用量过高还可能导致毒副作用。比如，过量的锌会妨碍铁和铜等其他营养成分吸收。而矿物质硒过量会导致神经受损，最近还与糖尿病风险升高联系起来。

    科学家们早已了解到，维他命、矿物质和其他营养成分可充当抗氧化剂，在免疫系统中扮演重要角色。它们可以保护细胞不受氧化应激影响并予以修复，氧化应激是被称为自由基的分子导致的损害。

    营养学家普遍认为，摄取均衡营养的最佳途径是均衡饮食，其中要包括大量新鲜水量和蔬菜、精益蛋白质和膳食纤维。

    营养专家说，要提升免疫力，至关重要的是避免加工食品，尽可能减少摄入动物产品和棕榈油、椰子油等植物油中所含的反式脂肪和不健康的饱和脂肪。相反，人们应当吃橄榄油等富含不饱和脂肪的食品。