4.12: Determining Amounts Needed

How much of these nutrients do we need? Scientists use methods that range from simply estimating the amount consumed by normal, healthy populations, to using sophisticated lab equipment to determine precisely the individual requirement for each person recruited for these special studies.

As expected, individual needs vary within a certain range, just as they vary in other measures like height and weight—normal variation (Figure 4.1). Most adults are about 5 to 6½ feet tall. Some are outside this range, but usually not by much. Adults 3 or 8 feet tall are unusual.

Nutrient needs of a specific person can’t be determined without measuring that person individually. This is expensive, tedious, and usually requires long-term confinement. Estimates of averages and the range of variation of nutrient needs are derived from numerous studies, and generous recommendations are made to cover the needs of a population adequately.

Individual requirements (as well as body weight, test scores, etc.) are generally distributed in a bell-shaped distribution called a normal curve (Figure 4.1). Most people are near the average. The further one moves away from the average, the fewer people there are.

This normal variation is taken into account in setting dietary recommendations. It’s like deciding what the standard height for doorways should be. Everyone needn’t be measured. Even without measuring anyone, you can make a good estimate by measuring old, existing doorways.

A standard doorway is high enough for most people to pass through without having to duck (the recommended intake meets most people’s need). Even people taller than the doorway need only duck, not crawl (for the few with higher needs, it isn’t higher by much). What a specific person needs in doorway height (the amount of a nutrient) can be determined only by measuring that particular person.

Figure 4.1: The Normal Curve