CONCEPTS IN BIOLOGY

PART VI. PHYSIOLOGICAL PROCESSES

 

25. Nutrition. Food and Diet

 

25.3. Dietary Reference Intakes

 

The U.S. Department of Agriculture (USDA) regularly publishes updated guidelines for maintaining good nutritional health. The current guidelines, the Dietary Reference Intakes, provide information on the amounts of certain nutrients various members of the public should receive. These daily guidelines are very detailed. There are different guidelines for children, men, and women by age group. There are also specific guidelines for pregnant and nursing mothers. There are also guidelines about the maximum amount of certain nutrients that people should get.

Dietary Reference Intakes are used when preparing product labels. By law, labels must list ingredients from the greatest to the least in quantity. In addition to carbohydrates, fats, proteins, and fiber, about 25 vitamins and minerals have Dietary Reference Intakes. Table 25.4 gives examples of some of the more common nutrients and their reference amounts for young adults.

 

TABLE 25.4. Dietary Reference Intakes for Some Common Nutrients

 

Nutrient

Women, 19-30 Years Old

Men, 19-30 Years Old

Maximum, Persons 19-30 Years Old

Value of Nutrient

Carbohydrates

130 g/day (45-65% of Calories)

130 g/day (45-65% of Calories)

No maximum set but refined sugars should not exceed 25% of total Calories

A source of energy

Proteins

46 g/day (10-35% of Calories)

56 g/day (10-35% of Calories)

No maximum but high- protein diets stress kidneys

Proteins are structural components of all cells; there are 10 essential amino acids that must be obtained in the diet

Fats

20-35% of Calories

20-35% of Calories

Up to 35% of total Calories

Energy source and building blocks for many molecules needed

Saturated and trans fatty acids

As low as possible

As low as possible

Less than 10% of Calories

 

Linoleic acid

12 g/day

17 g/day

No maximum set

Essential fatty acid needed for enzyme function and maintenance of epithelial cells

Linolenic acid

1.1 g/day

1.6 g/day

No maximum set

Essential fatty acid needed to reduce coronary heart disease

Cholesterol

As low as possible

As low as possible

Less than 300 mg/day

None needed, because the liver makes cholesterol

Water

2.7 liters/day

3.7 liters/day

No maximum set

 

Total fiber

28 g/day

34 g/day

No maximum set

Improve gut function

Calcium

1 g/day

1 g/day

2.5 g/day

Needed for the structure of bones and many other functions

Iron

18 g/day

8 g/day

45 g/day

Needed to build the hemoglobin of red blood cells

Sodium

1.5 g/day

1.5 g/day

2.3 g/day (most people exceed this limit)

Needed for normal cell function

Vitamin A

700 μg/day

900 μg/day

3,000 μg/day

Maintains skin and intestinal lining

Vitamin C

75 mg/day

90 mg/day

2,000 mg/day

Maintains connective tissue and skin

Vitamin D

5 μg/day

5 μg/day

50 μg/day

Needed to absorb calcium for bones

 

25.3. CONCEPT REVIEW

6. How much of each of the following nutrients should you get each day: iron, calcium, protein, and fiber?