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Good nutrition aims to achieve and maintain a desirable body composition and high potential for physical and mental work. Balancing energy intake with energy expenditure is necessary for a desirable body weight. Energy expenditure depends on age, sex, weight (see Table 4: Nutrition: General Considerations: Recommended Dietary Reference Intakes* for Some Macronutrients, Food and Nutrition Board, Institute of Medicine of the National Academies ), and metabolic and physical activity. If energy intake exceeds expenditure, weight is gained. Taking in about 100 calories/day more than needed results in a weight gain of about 4 to 5 kg in a year. If energy intake is less than expenditure, weight is lost.
Daily dietary requirements for essential nutrients also depend on age, sex, weight, and metabolic and physical activity. Every 5 yr, the Food and Nutrition Board of the National Academy of Sciences/National Research Council and the US Department of Agriculture (USDA) issues the dietary reference intakes (DRIs) for protein, energy, and some vitamins and minerals (see Table 4: Nutrition: General Considerations: Recommended Dietary Reference Intakes* for Some Macronutrients, Food and Nutrition Board, Institute of Medicine of the National Academies, Table 1: Vitamin Deficiency, Dependency, and Toxicity: Recommended Daily Intakes for Vitamins, and Table 2: Mineral Deficiency and Toxicity: Guidelines for Daily Intake of Minerals). For vitamins and minerals about which less is known, safe and adequate daily dietary intakes are estimated.
Pregnant women (see Approach to the Pregnant Woman and Prenatal Care: Diet and supplements) and infants (see Approach to the Care of Normal Infants and Children: Nutrition in Infants) have special nutritional needs. Detailed recommendations are available from the Food and Nutrition Board.
The USDA publishes the Food Guide Pyramid, which specifies the number of recommended daily servings of various food groups. The recommendations are individualized based on age, sex, and physical activity (see Table 5: Nutrition: General Considerations: Recommended Dietary Intake for 40-Yr-Olds With Moderate Physical Activity*). Individualized recommendations can be obtained by entering the relevant information at the USDA web site.
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Table 5
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| Recommended Dietary Intake for 40-Yr-Olds With Moderate Physical Activity* |
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Food Groups
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Amount/Day
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Men
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Women
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Grains†
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9 oz
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6 oz
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Vegetables‡
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3.5 cups
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2.5 cups
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Fruits
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2 cups
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2 cups
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Milk
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3 cups
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3 cups
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Meat and beans
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6.5 oz
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5.5 oz
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Oils
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8 tsp
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6 tsp
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Sugars and fats
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410 calories
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265 calories
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Estimated daily intake§
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2600 calories
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2000 calories
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*About 30 to 60 min of moderate or vigorous activity (eg, brisk walking, jogging, biking, aerobic exercise, yard work) daily.
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†At least half should be whole grains.
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‡People should vary the vegetables they eat and include beans and peas, dark green vegetables (eg, broccoli, greens, lettuce, spinach), orange vegetables (eg, carrots, sweet potatoes, winter squash), starchy vegetables (eg, corn, potatoes), and other vegetables (eg, asparagus, cauliflower, mushrooms, tomatoes).
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§Actual needed intake is determined by monitoring trends in body weight.
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Note: Individualized recommendations can be obtained by entering the relevant information at the USDA web site (www.mypyramid.gov).
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Generally, the recommended intake decreases with aging because physical activity tends to decrease, resulting in less energy expended. The new Food Guide Pyramid emphasizes the following:
Adequate fluid intake is also important.
Fats should constitute ≤ 30% of total calories, and saturated and trans fatty acids should constitute < 10%. Excess intake of saturated fats contributes to atherosclerosis. Substituting polyunsaturated fatty acids for saturated fats can decrease the risk of atherosclerosis. Routine use of nutritional supplements is not necessary or beneficial; some supplements can be harmful. For example, excess vitamin A can lead to hypervitaminosis A, with headaches, osteoporosis, and rash.
Last full review/revision July 2007 by Margaret-Mary G. Wilson, MD
Content last modified July 2007
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