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，大多數人都知道他們應該吃更多的蔬菜。但有沒有從您已經吃的蔬菜中獲得更多營養的方法呢？

     對一個正在生長的身體的研究表明，當說到蔬菜，它不僅指我們吃的有多少，，而且指我們如何準備的，因為它影響進入我們的身體的蔬菜的化學物質，維生素和其他營養物質。

    多吃蔬菜的好處是顯而易見的。許多研究表明，那些消耗大量蔬菜的人，患心臟病，高血壓，糖尿病，眼部健康有問題，甚至癌癥的概率較低。根據哈佛大學公共衛生學院的最新的飲食指南，1天要求5至13 份 ---- 就是兩杯半至六杯半的量。

對一個人想要用1天的飲食為2000卡路里來保持她的體型的節食者來說-----即轉化為9份 ，或四杯半一天。但應該如何食用？

   奇怪的是，生的及未經加工的蔬菜并不總是最好的。在下個月的英國雜志營養上，研究人員將報道一個有關198名德國人嚴格遵守一個生食食物的飲食的研究，即95 ％的總的食物攝入量來自生食食物。他們正常水平的維生素A和相對較高的水平的β胡蘿卜素。

    但他們的番茄紅素較缺乏，而在西紅柿中發現的類胡蘿卜素和其他紅色色素的蔬菜是最強有力的抗氧化劑中的一個。近80 ％的人血漿中番茄紅素的水平，低于平均水平。“有一種誤解認為，生的食物都是比較好的” 史蒂芬k.克林頓說：，他是美國俄亥俄州州立大學腫瘤醫學部內部中醫藥的營養研究員和教授。“水果和蔬菜，很多時候一點點烹飪和一點點的處理，其實是很有幫助的” 。

    養份的數量和類型的最終結束是在蔬菜被放到菜盤之前受多項因素后，包括在何處和如何，他們生長，處理和儲存，然后才被購買。才來到您面前。沒有一種的烹調或制備方法是最好的。水溶性營養素像維生素C和B，以及所謂的一組多酚化合物的營養素，往往在處理時失去了。例如，研究表明，在6個月后，冷凍的櫻桃已失去高達50 ％的花青素，健康的化合物發現，在色素的紅色和藍色的水果和蔬菜。據由加州大學戴維斯匯編的數據，新鮮菠菜在煮后失去其64 ％維生素C 。罐頭裝的豌豆和胡蘿卜失去85 ％至95 ％的維生素C 。

     脂溶性化合物像維生素A ， D ， E和K，以及被稱為抗氧化的類胡蘿卜素的化合物是不太可能溶解在水中。煮食時也使植物的厚厚的細胞壁分離，釋放出我們身體所需的東西。這就是為什么處理過的番茄制品要比新鮮的西紅柿具有更高的番茄紅素含量。

     今年1月，，在農業和食品化學雜志上的一份報告得出結論認為，在對胡蘿卜，西葫蘆和花椰菜的各種烹飪方法中，煮比蒸，油炸或生食更好。油炸是最不可取的。

     然而，事物都是相對的。舉例來說，煮過的胡蘿卜，明顯增加了可衡量的類胡蘿卜素水平，但與生胡蘿卜相比，導致了完整的多酚類物質的損失。

      這份報告并沒有指出微波的影響，，但是2007年3月份的食品科學研究雜志上的一份研究指出煮，蒸，微波和擠壓的方法對青花菜的養分的影響。蒸和煮造成了22 ％至34 ％維生素C的損失， 而微波和擠壓則能保留90 ％的維生素C。

    拿什么伴著蔬菜吃也是很重要的。在俄亥俄州，對吃了辣茄醬和沙拉的人的血液中的濃度進行了測量研究。當辣茄醬或沙拉與脂肪豐富的鱷梨同吃或用全脂沙拉醬作輔料， 食用者比那些食用未加其它東西的蔬菜或用低脂肪作輔料的人吸收高達4倍以上的番茄紅素， 7倍以上葉黃素和18倍 的β胡蘿卜素。

     脂肪也能改善蔬菜的味道，也就是說，人會吃得更多。本月初，美國預防醫學雜志報告了對1500名青少年的采訪，，針對他們在高中及之后的大約四年的飲食習慣。在十幾歲的年齡段，許多因素會影響他們攝入水果和蔬菜的數量。對20歲年齡段的研究表明，口味是影響水果和蔬菜的消費的唯一的因素。年輕的成年人不愿吃蔬菜，只是因為他們不喜歡的口味。

    在蔬菜里放些調料----香料，少許鹽---使它更好地品味，這可以提高您的飲食經驗，使食品的口味更好，使您更可能，更經常地吃蔬菜， ”克林頓博士說。因為養分含量和品位可以有所不同，所以烹調以及如何準備蔬菜方法多種多樣，最主要的是要吃以各種方式制作的各種蔬菜。蘇珊·羅伯茨在擔任塔夫茨大學弗里德曼營養學校的能量代謝實驗室主任時說過， “吃各種蔬菜是特別重要的，您要漸漸喜歡它們并吃得更多” 。

    在蔬菜里放些調料----香料，少許鹽---使它更好地品味，這可以提高您的飲食經驗，使食品的口味更好，使您更可能，更經常地吃蔬菜， ”克林頓博士說。

    因為養分含量和品位可以有所不同，所以烹調以及如何準備蔬菜方法多種多樣，最主要的是要吃以各種方式制作的各種蔬菜。

    蘇珊·羅伯茨在擔任塔夫茨大學弗里德曼營養學校的能量代謝實驗室主任時說過， “吃各種蔬菜是特別重要的，您要漸漸喜歡它們并吃得更多” 。