Why Food Scientists Never Say “Never” …or “Always”

　　为什么食品科学家们从来不说“从来不”……或者“总是”

　　by Faith Hickman Brynie

　　Look through this book for statements that limit the conclusions food scientists draw from their research. You’ll find dozens of words and phrases such as “usually,” “often,” “sometimes,” “some people,” “on the average,” “perhaps,” and so on. The reason for this is that a “one size fits all” approach does not apply to nutrition science.

　　For example, the current Recommended Dietary Allowances (RDAs) for fat, calcium, or other nutrients are simply “recommendations.” Although they differ by gender and by age group, the recommendations are estimates based on data obtained from a fairly small group of volunteers. The allowances are set to be two standard deviations above the mean (average) requirement for a given nutrient for a given group, based on the scientific findings for the group. They should cover the needs of 97.5 percent of the population within a given age or gender category. The fact is, you could have your very own nutrient requirements determined, but it would be terribly costly, and would likely bear strong resemblance to the current RDAs.

　　When it comes to measuring the effects of one dietary change, such as adding oatmeal to the diet to reduce the chance of developing heart disease, it is much more difficult to make definitive statements about the general public. Here are some reasons why:

　　● Individuals differ in their response to food. What happens in one person won誸 necessarily happen in another.

　　● A change in diet may make a person feel better, simply because of the change. When we expect an improvement, we usually get it.

　　● It’s hard to alter a single factor without altering others. Add a food to the diet and you are adding other substances besides the nutrient you are interested in. That’s why food research is often done with supplements.

　　● Poor nutrition is not the only reason for depression or forgetfulness. In human research, it’s difficult to account for all factors such as age, sex, family background, education, social or family problems, and many others.

　　● Small differences in amounts or even the time of day can influence results. For example, skipping breakfast reduces mental performance, but a very large breakfast impairs concentration. Also, carbohydrate food may energize in the morning but relax if eaten in the evening.

　　● The effects of a dietary deficiency cannot be studied in a controlled way. It would be wrong to purposely deprive people of an essential nutrient in order to study the effects.

　　● Variables such as memory, intelligence, or mood are hard to define and even harder to measure.

　　● Some studies depend on the self-reports of subjects. People give an initial medical history that may not be accurate. If a person claims to feel happier after a change in diet, who can challenge that report－or verify it?

　　● Trends can predict what happens in a large population, but they can’t predict for an individual. What’s true for most people or the average person may not be true for you, your friend, or your neighbor.

　　浏览本书，找出一些语句，可以限制食品科学家通过研究得出的结论。你会发现几十个诸如“通常”、“经常”、“有时”、“有些人”、“一般”、“也许”的字眼。原因是那种一通百通的研究方法对于营养科学是不适用的。

　　例如，当今的推荐日摄食量（RDAs）中对脂肪、钙或其他营养素的允许摄入量仅仅是一种建议。尽管这些摄入量随着性别和年龄段的不同而不同，这些建议是根据从一小部分志愿者那里得到的数据所作出的估计。这些摄入量被定为在特定一组人中对一种特定营养素的平均需求之上的两个标准偏差。这种计算是依据对那组人的科学调查的结果。这些数据应当涵盖某一特定年龄和性别的97.5%人群的需要。事实上，你本可以确定自己对营养素的需要，但这样做是非常昂贵的，而且结果也会和目前的推荐日摄食量的结果非常相似。

　　涉及测量饮食中某一变化所带来的影响时，比如，为了减少患心脏病的几率而在饮食中增加燕麦，那就更难针对整个公众做出确定的规定了。原因如下：

　　● 每个人对食物做出的反应不一样。在一个人身上发生的事情并不一定会在另一个人身上发生。

　　● 饮食结构的改变可能仅仅是因为改变本身使人感觉好一些。当我们期望得到改进时，我们通常就会感到这一效果。

　　● 我们很难在不改变其他因素的情况下改变其中的某个因素。如果把一种食物加入到饮食结构中去，那么你不但加入了你感兴趣的营养素，你同时还加入了一些其他物质。这就是为什么食物研究是一个不断补充与发现的过程。

　　● 营养不良并不是导致情绪低落和健忘的惟一原因。在对人的研究当中，很难对诸如年龄、性别、家庭背景、受教育情况、社会和家庭问题以及其他许多因素作出满意的解释。

　　● 数量上微小的差异甚至一天中不同的时间都会影响到研究的结果。例如，不吃早餐会降低人的脑筋反应力，而早饭吃得过于丰盛会影响人的注意力。另外，早上吃碳水化合物会使人精力充沛，而晚上吃会使人放松。

　　● 营养不良症不能在一种控制的状态下进行研究。为了获得实验结果而有目的地剥夺人所需的基本营养素的做法是不对的。

　　● 很难定义，甚至更难测量一些可变因素，如记忆力、智力和情绪。

　　● 有些研究依赖于实验对象的自我汇报。这些人提供的既往病史可能是不准确的。如果一个人说饮食结构改变后，他感到更幸福一些，又有谁能对这一报告提出异议或是证明它呢？

　　● 趋势可以预测群体中将要发生的情况，但不能对个体进行预测。对“大多数人”或“一般人”来说是对的，却可能对你、你的朋友或你的邻居来说并不对。