As new studies and observations constantly alter our understanding of how what we eat affects our bodies, tracking the evolving rules of good nutrition becomes ever more challenging.
For example, eight years ago, when Facts On File published the first edition of The New Complete Book of Food, it was commonly accepted that high-fiber diet could reduce the risk of colon cancer, beta-carotene, a yellow pigment in deep orange and dark green vegetables, would protect against cancer of the throat and lungs, fruit juice was healthful for kids—in fact, the more the better, and folic acid, a B vitamin, might lower the odds of suffering a second heart attack.
Today, none of these four beliefs are considered to be true. In the years between editions of this book, nutrition researchers have discovered that how much fiber you eat does not affect your risk of colon cancer; beta-carotene makes plant foods look good but is almost certainly not protective; fruit juice is loaded with sugar and too much is, well, too much; folic acid does lower the risk of birth defects but doesn’t influence the chances of a second coronary event.
Another major change in nutrition science is how we measure the specific amounts of the various nutrients we require to maintain optimum health. Eight years ago, food scientists commonly used the term recommended dietary allowance (RDA) to signify healthful quantities of vitamins, minerals, and other nutrients such as protein, fat, carbohydrates, and dietary fiber. Today, a new umbrella term—dietary reference intake (DRI)—includes three different measurements:
The Recommended Dietary Allowance (RDA) is a scientifically established daily level of a nutrient known to meet the nutritional needs of as many as 98 percent of healthy individuals. One example of an RDA is the 90 mg per day of vitamin C recommended for healthy adult males.
The Adequate Intake (AI) is a daily quantity assigned to nutrients for which there is not yet enough evidence to establish.
