To stay healthy, adequate amounts of energy and of each of the essential nutrients must be consumed in the diet. The exact amount of each that you need depends on your age, size, sex, genetic makeup, lifestyle, and health status. The Dietary Reference Intakes (DRI s) are general recommendations for the amounts of energy (calories), nutrients, and other substances that should be consumed on an average daily basis in order to promote health, prevent deficiencies, and reduce the incidence of chronic disease.
The DRIs include recommendations for different groups of people based on age, gender, and, when appropriate, pregnancy and lactation. The recommendations for nutrient intakes include four different types of values. The Estimated Average Requirements (EAR s) are the amounts of nutrients that are estimated to meet the average needs of the population. They are not used to assess individual intake but rather are intended for planning and evaluating the adequacy of the nutrient intake of population groups.
The Recommended Dietary Allowances (RDA s) and Adequate Intakes (AI s) are values that are calculated to meet the needs of nearly all healthy people in each gender and life-stage group. These can be used to plan and assess individual's diets. The fourth set of DRI values is the Tolerable Upper Intake Levels (ULs).
These are the maximum levels of intake that are unlikely to pose a risk of adverse health effects. ULs can be used as a guide to limit intake and evaluate the possibility of excessive intake. When your diet provides the RDA or AI for each nutrient and does not exceed the UL for any, your risk of nutrient deficiency or toxicity is low.
The recommendations for energy intake are expressed as Estimated Energy Requirements (EERs). These values predict the calories needed to maintain weight in healthy individuals. They are based on age, gender, body size, and activity level.
Consuming either too much or too little of one or more nutrients or energy can cause malnutrition. Typically, we think of malnutrition as a lack of energy or nutrients. This may occur if someone doesn't include enough in their diet, but it is also caused by an increase in energy or nutrient requirements, or an inability to absorb or use nutrients.
Energy deficiency is called starvation. It causes a loss of body fat and muscle mass, resulting in an emaciated appearance. Malnutrition due to individual nutrient deficiencies causes symptoms that reflect the functions of the nutrient in the body. For example, vitamin D is needed for strong bones. A deficiency of this vitamin causes the leg bones of children to bow outward because they are too weak to support their body weight.
Vitamin A is needed for healthy eyes; a deficiency can result in blindness. For many nutrient deficiencies, supplying the lacking nutrient can quickly reverse the symptoms.
Overnutrition, an excess of energy or nutrients, is also a form of malnutrition. An excess of energy causes obesity. It increases the risk of developing diseases such as diabetes and heart disease. Excesses of vitamins and minerals rarely occur from eating food but are seen with overuse of dietary supplements. For example, consuming too much vitamin B6 can cause nerve damage and excess iron intake can cause liver failure.
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