By now, most people know they should be eating more vegetables. But are there ways to get more from the vegetables you already eat?

    A growing body of research shows that when it comes to vegetables, it’s not only how much we eat, but how we prepare them, that influences the amount of phytochemicals, vitamins and other nutrients that enter our body. 

    The benefits are significant. Numerous studies show that people who consume lots of vegetables have lower rates of heart disease, hypertension, diabetes, eye problems and even cancer. The latest dietary guidelines call for 5 to 13 servings — that is two and a half to six and a half cups a day. For a person who maintains her weight on a 2,000-calorie-a-day diet, this translates into nine servings, or four and a half cups a day, according to the Harvard School of Public Health. But how should they be served?

    Surprisingly, raw and plain vegetables are not always best. In The British Journal of Nutrition next month, researchers will report a study involving 198 Germans who strictly adhered to a raw food diet, meaning that 95 percent of their total food intake came from raw food. They had normal levels of vitamin A and relatively high levels of beta carotene. 

    But they fell short when it came to lycopene, a carotenoid found in tomatoes and other red-pigmented vegetables that is one of the most potent antioxidants. Nearly 80 percent of them had plasma lycopene levels below average. 

    “There is a misperception that raw foods are always going to be better,” says Steven K. Clinton, a nutrition researcher and professor of internal medicine in the medical oncology division at Ohio State University. “For fruits and vegetables, a lot of times a little bit of cooking and a little bit of processing actually can be helpful.”

    The amount and type of nutrients that eventually end up in the vegetables are affected by a number of factors before they reach the plate, including where and how they were grown, processed and stored before being bought. Then, it’s up to you. No single cooking or preparation method is best. Water-soluble nutrients like vitamins C and B and a group of nutrients called polyphenolics are often lost in processing. For instance, studies show that after six months, frozen cherries have lost as much as 50 percent of anthocyanins, the healthful compounds found in the pigment of red and blue fruits and vegetables. Fresh spinach loses 64 percent of its vitamin C after cooking. Canned peas and carrots lose 85 percent to 95 percent of their vitamin C, according to data compiled by the University of California, Davis.

    Fat-soluble compounds like vitamins A, D, E and K and the antioxidant compounds called carotenoids are less likely to leach out in water. Cooking also breaks down the thick cell walls of plants, releasing the contents for the body to use. That is why processed tomato products have higher lycopene content than fresh tomatoes.

    In January, a report in The Journal of Agriculture and Food Chemistry concluded that over all, boiling was better for carrots, zucchini and broccoli than steaming, frying or serving them raw. Frying was by far the worst.. 

    Still, there were tradeoffs. Boiling carrots, for instance, significantly increased measurable carotenoid levels, but resulted in the complete loss of polyphenols compared with raw carrots. 

    That report did not look at the effects of microwaving, but a March 2007 study in The Journal of Food Science looked at the effects of boiling, steaming, microwaving and pressure cooking on the nutrients in broccoli. Steaming and boiling caused a 22 percent to 34 percent loss of vitamin C. Microwaved and pressure-cooked vegetables retained 90 percent of their vitamin C. 

    What accompanies the vegetables can also be important. Studies at Ohio State measured blood levels of subjects who ate servings of salsa and salads. When the salsa or salad was served with fat-rich avocados or full-fat salad dressing, the diners absorbed as much as 4 times more lycopene, 7 times more lutein and 18 times the beta carotene than those who had their vegetables plain or with low-fat dressing.

    Fat can also improve the taste of vegetables, meaning that people will eat more of them. This month, The American Journal of Preventive Medicine reported on 1,500 teenagers interviewed in high school and about four years later on their eating habits. In the teenage years, many factors influenced the intake of fruits and vegetables. By the time the study subjects were 20, the sole factor that influenced fruit and vegetable consumption was taste. Young adults were not eating vegetables simply because they didn’t like the taste.

    “Putting on things that make it taste better — spices, a little salt — can enhance your eating experience and make the food taste better, so you’re more likely to eat vegetables more often,” Dr. Clinton said. 

    Because nutrient content and taste can vary so widely depending on the cooking method and how a vegetable is prepared, the main lesson is to eat a variety of vegetables prepared in a variety of ways. 

    As Susan B. Roberts, director of the energy metabolism laboratory at the Tufts University Friedman School of Nutrition, put it, “Eating a variety of veggies is especially important so you like them enough to eat more.” 

    如今，大多数人都知道他们应该吃更多的蔬菜。但有没有从您已经吃的蔬菜中获得更多营养的方法呢？

     对一个正在生长的身体的研究表明，当说到蔬菜，它不仅指我们吃的有多少，，而且指我们如何准备的，因为它影响进入我们的身体的蔬菜的化学物质，维生素和其他营养物质。

    多吃蔬菜的好处是显而易见的。许多研究表明，那些消耗大量蔬菜的人，患心脏病，高血压，糖尿病，眼部健康有问题，甚至癌症的概率较低。根据哈佛大学公共卫生学院的最新的饮食指南，1天要求5至13 份 ---- 就是两杯半至六杯半的量。

对一个人想要用1天的饮食为2000卡路里来保持她的体型的节食者来说-----即转化为9份 ，或四杯半一天。但应该如何食用？

   奇怪的是，生的及未经加工的蔬菜并不总是最好的。在下个月的英国杂志营养上，研究人员将报道一个有关198名德国人严格遵守一个生食食物的饮食的研究，即95 ％的总的食物摄入量来自生食食物。他们正常水平的维生素A和相对较高的水平的β胡萝卜素。

    但他们的番茄红素较缺乏，而在西红柿中发现的类胡萝卜素和其他红色色素的蔬菜是最强有力的抗氧化剂中的一个。近80 ％的人血浆中番茄红素的水平，低于平均水平。“有一种误解认为，生的食物都是比较好的” 史蒂芬k.克林顿说：，他是美国俄亥俄州州立大学肿瘤医学部内部中医药的营养研究员和教授。“水果和蔬菜，很多时候一点点烹饪和一点点的处理，其实是很有帮助的” 。

    养份的数量和类型的最终结束是在蔬菜被放到菜盘之前受多项因素后，包括在何处和如何，他们生长，处理和储存，然后才被购买。才来到您面前。没有一种的烹调或制备方法是最好的。水溶性营养素像维生素C和B，以及所谓的一组多酚化合物的营养素，往往在处理时失去了。例如，研究表明，在6个月后，冷冻的樱桃已失去高达50 ％的花青素，健康的化合物发现，在色素的红色和蓝色的水果和蔬菜。据由加州大学戴维斯汇编的数据，新鲜菠菜在煮后失去其64 ％维生素C 。罐头装的豌豆和胡萝卜失去85 ％至95 ％的维生素C 。

     脂溶性化合物像维生素A ， D ， E和K，以及被称为抗氧化的类胡萝卜素的化合物是不太可能溶解在水中。煮食时也使植物的厚厚的细胞壁分离，释放出我们身体所需的东西。这就是为什么处理过的番茄制品要比新鲜的西红柿具有更高的番茄红素含量。

     今年1月，，在农业和食品化学杂志上的一份报告得出结论认为，在对胡萝卜，西葫芦和花椰菜的各种烹饪方法中，煮比蒸，油炸或生食更好。油炸是最不可取的。

     然而，事物都是相对的。举例来说，煮过的胡萝卜，明显增加了可衡量的类胡萝卜素水平，但与生胡萝卜相比，导致了完整的多酚类物质的损失。

      这份报告并没有指出微波的影响，，但是2007年3月份的食品科学研究杂志上的一份研究指出煮，蒸，微波和挤压的方法对青花菜的养分的影响。蒸和煮造成了22 ％至34 ％维生素C的损失， 而微波和挤压则能保留90 ％的维生素C。

    拿什么伴着蔬菜吃也是很重要的。在俄亥俄州，对吃了辣茄酱和沙拉的人的血液中的浓度进行了测量研究。当辣茄酱或沙拉与脂肪丰富的鳄梨同吃或用全脂沙拉酱作辅料， 食用者比那些食用未加其它东西的蔬菜或用低脂肪作辅料的人吸收高达4倍以上的番茄红素， 7倍以上叶黄素和18倍 的β胡萝卜素。

     脂肪也能改善蔬菜的味道，也就是说，人会吃得更多。本月初，美国预防医学杂志报告了对1500名青少年的采访，，针对他们在高中及之后的大约四年的饮食习惯。在十几岁的年龄段，许多因素会影响他们摄入水果和蔬菜的数量。对20岁年龄段的研究表明，口味是影响水果和蔬菜的消费的唯一的因素。年轻的成年人不愿吃蔬菜，只是因为他们不喜欢的口味。

    在蔬菜里放些调料----香料，少许盐---使它更好地品味，这可以提高您的饮食经验，使食品的口味更好，使您更可能，更经常地吃蔬菜， ”克林顿博士说。因为养分含量和品位可以有所不同，所以烹调以及如何准备蔬菜方法多种多样，最主要的是要吃以各种方式制作的各种蔬菜。苏珊·罗伯茨在担任塔夫茨大学弗里德曼营养学校的能量代谢实验室主任时说过， “吃各种蔬菜是特别重要的，您要渐渐喜欢它们并吃得更多” 。

    在蔬菜里放些调料----香料，少许盐---使它更好地品味，这可以提高您的饮食经验，使食品的口味更好，使您更可能，更经常地吃蔬菜， ”克林顿博士说。

    因为养分含量和品位可以有所不同，所以烹调以及如何准备蔬菜方法多种多样，最主要的是要吃以各种方式制作的各种蔬菜。

    苏珊·罗伯茨在担任塔夫茨大学弗里德曼营养学校的能量代谢实验室主任时说过， “吃各种蔬菜是特别重要的，您要渐渐喜欢它们并吃得更多” 。