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Overview of Nutritional Support
Many undernourished people (see Undernutrition) need additional nutrition (nutritional support). Usually, undernourished people need to consume more calories as well as more nutrients such as vitamins and minerals. Nutritional support is intended to increase the amount of muscle tissue (muscle mass).
Nutrients are given by mouth whenever possible, ideally as regular food. Several strategies can be used if people are reluctant to eat:
However, these strategies are not enough for some people. For example, these strategies do not help people who cannot eat because of injuries or other physical problems (such as difficulty swallowing) or who have difficulty absorbing nutrients. These people may need nutritional support (sometimes called artificial feeding because it uses commercial nutrient mixtures rather than food). Nutrients can be given through a tube (tube feeding—see Tube Feeding), usually inserted through the nose, or through a catheter inserted in a vein (intravenous feeding—see Intravenous Feeding). With tube feedings, nutrients go directly into the stomach or small intestine.
If people are dying or have advanced dementia, artificial feeding is usually not recommended (see Nutritional Support for People Who Are Dying or Severely Demented).
Before starting nutritional support, doctors must first determine the amount and mix of nutrients the person needs. People need a certain amount of nutrients for energy, which is measured in calories. The number of calories people need varies depending on their weight, their activity level, and the demands created by illness. The mix of nutrients typically includes carbohydrates, protein, fat, vitamins, minerals, fiber, and fluids. Usually, doctors estimate the person's needs using equations based on the person's weight, height, age, sex, and activity level. Doctors adjust the requirements if the person has a condition that increases the need for calories, such as a serious illness, kidney failure, an infection, an injury, or recent surgery. Some centers use a special technique to obtain a more accurate estimate. This technique measures how much oxygen is inhaled and how much carbon dioxide is exhaled—an indication of how much energy the body is using.
Health care practitioners must carefully manage artificial feeding methods to make sure people are receiving the nutrients they need and to prevent problems, such as infections. To determine whether nutritional support is appropriate and effective, doctors regularly monitor factors such as the following:
Body mass index (BMI—weight in kilograms divided by height in meters squared)
Body composition (the amount of fat and muscle tissue—see Figure: Fat Versus Lean: Body Composition)
Substances in blood, urine, and stool that indicate nutritional status
Muscle strength (for example, by measuring how strong the hand grip is)
An increase in muscle strength indicates an increase in muscle mass and thus improved nutritional status.
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