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Nutritional Requirements

by Adrienne Youdim, MD

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: 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. 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: Recommended Dietary Reference Intakes* for Some Macronutrients, Food and Nutrition Board, Institute of Medicine of the National Academies, Recommended Daily Intakes for Vitamins, and 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 Nutrition in Infants) have special nutritional needs.

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: 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 using the Supertracker tool.

Recommended Dietary Intake for 40-Yr-Olds With Moderate Physical Activity*

Food Groups

Amount/Day

Men

Women

Grains

9 oz

6 oz

Vegetables

3.5 cups

2.5 cups

Fruits

2 cups

2 cups

Milk

3 cups

3 cups

Meat and beans

6.5 oz

5.5 oz

Oils

8 tsp

6 tsp

Sugars and fats

410 calories

265 calories

Estimated daily intake §

2600 calories

2000 calories

*About 30 to 60 min of moderate or vigorous activity (eg, brisk walking, jogging, biking, aerobic exercise, yard work) daily.

At least half should be whole grains.

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).

§ Actual needed intake is determined by monitoring trends in body weight.

Note: Individualized recommendations can be obtained by entering the relevant information at the USDA web site ( USDA web site ) using the Supertracker tool.

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:

  • Increasing consumption of whole grains

  • Increasing consumption of vegetables and fruits

  • Substituting fat-free or low-fat milk products (or equivalents) for whole-fat milk products

  • Reducing consumption of saturated fats and trans fatty acids

  • Exercising regularly

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.

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