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http://www.sina.com.cn 2004/11/04 19:00  ÐÂÀ˽ÌÓý

¡¡¡¡Why Food Scientists Never Say ¡°Never¡± ¡­or ¡°Always¡±

¡¡¡¡ÎªÊ²Ã´Ê³Æ·¿Æѧ¼ÒÃÇ´ÓÀ´²»Ëµ¡°´ÓÀ´²»¡±¡­¡­»òÕß¡°×ÜÊÇ¡±

¡¡¡¡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 ap
ply 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:

¡¡¡¡¡ñ Individuals differ in their response to food. What happens in one person wonÕt necessarily happen in another.

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

¡¡¡¡¡ñ 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.

¡¡¡¡¡ñ 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.

¡¡¡¡¡ñ 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.

¡¡¡¡¡ñ 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.

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

¡¡¡¡¡ñ 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?

¡¡¡¡¡ñ 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.

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