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How can both nutrient deficiencies and nutrient excesses cause malnutrition?

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USDA MyPlate dietary guidelines — human nutrition MyPlate, a revised set of dietary guidelines introduced by the U.S. Department of Agriculture (USDA) in 2011, divides the four basic food groups (fruits, grains, protein, and vegetables) into sections on a plate, the size of each section representing the relative dietary proportions of each food group. The small blue circle shown at the upper right illustrates the inclusion and recommended proportion of dairy products in the diet.

Malnutrition is defined as an impaired physical condition resulting from a prolonged deficiency or excess of total energy or specific nutrients, such as protein, vitamins, or minerals.1

Nutrient Deficiencies

Deficiencies occur when the body does not receive enough nutrients to meet its physiological needs. This can be primary, caused by inadequate dietary intake due to poverty, limited food availability, or poor food choices. Alternatively, it can be secondary, where the body is unable to properly digest, absorb, or metabolize nutrients due to metabolic defects or chronic illness. Prolonged deficiencies lead to specific nutritional diseases, such as scurvy or rickets, characterized by symptoms like fatigue, stunted growth, and organ dysfunction.231

Nutrient Excesses

Malnutrition also arises from the overconsumption of nutrients, often through the overzealous use of dietary supplements. Excessive intake can reach toxic levels, causing direct harm to the body. For example, hypervitaminosis A can cause liver damage, while excessive iron intake can lead to corrosive damage to the digestive tract. Thus, both extremes disrupt normal metabolic function and overall health.142