Nutrition and physical activity are the two most important influences on health. It is the balance of nutrients contained in the calories you consume weighed against the calories you burn that specifically impacts your health. Nutritional imbalances like overnutrition and undernutrition may lead to severe health difficulties. Always consult a physician before you make any dietary changes.
Overnutrition is frequent or habitual overconsumption of nutrients by eating too much food to the point that it becomes dangerous to your health. Nutrients are all compounds necessary for bodily function, including minerals, vitamins, fats, carbohydrates and proteins. Although most nutrients can be harmful in excess, the danger of overnutrition relates mostly to carbohydrates and fats. Overeating differs conceptually from overnutrition, although they are essentially the same thing in action; whereas overeating is a compulsion considered a psychological disorder, overnutrition is volitionally choosing to eat more food than you need, even if you don't realize it.
Undernutrition is the opposite of overnutrition, meaning that it is a nutrient deficiency from not eating enough food. Undernutrition usually affects the balance of all the nutrients in your body. Nonetheless, problems relating to a deficiency in carbohydrates and fats will manifest first and most acutely. Initially, the body starts using its glycogen -- or sugar -- reserves, stored water and body protein. Then, your body consumes stored fatty acids and lean muscle. These two effects of undernutrition result in a dramatic decrease in body weight. Short-term undernutrition is possible if you inexplicably lose at least 10 percent of your body weight over three to six months.
Undernutrition is a form of malnutrition -- a condition resulting from not consuming enough nutrients. However, it is not synonymous with undereating -- it can occur despite overeating. This is because proper nutrition requires a balance of all nutrients not present in all foods; this means that your body requires a balance of many different foods. Even in the case of overnutrition, when you may be eating too much food, you can still develop a deficiency in certain nutrients if you fail to consume the proper variety foods. In this way, you can be both overnourished and malnourished. Other causes of malnutrition unrelated to the amount of food you eat include digestion or absorption problems and certain medical conditions.
A common misconception is that malnutrition, particularly in babies or healthy adults and children, is uncommon in developed countries -- the issue that garners far more attention is obesity relating to overeating. In fact, people in developed countries have a relatively high risk for deficiencies in several nutrients, according to the International Association of Infant Food Manufacturers. These nutrients differ by country; for example, whereas thiamin deficiencies may occur in Asia, pyridoxine deficiencies are more common in Finland and zinc deficiencies happen more frequently in the U.S. Other nutrients with a higher likelihood for deficiency than others in the U.S. include vitamin K in babies, as breast milk contains little vitamin K and D; vitamin D due to limited sun exposure; and iron, which frequently causes iron deficiency anemia.