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?