Observations from different parts of the world show that low protein intakes, often accompanied by low calorie intakes, occur in adults in many developing countries. In the industrialized world, excessive consumption of lipids, carbohydrates, sugars and alcohol (empty calories) without essential nutrients given by a balanced diet, make dietary considerations the major factor in most deadly diseases. The malnourished adult usually shows seasonal deficiencies, which are transient and do not cause obvious ill-health unless accompanied by acute or chronic disease. Dietary imbalance shows in reduced physical output in work among adults and developmental problems among children. An additional effect is a deterioration in the use of mental faculties - namely listlessness, lowering of initiative, lack of awareness, poor judgement, etc. At any age, poor nutrition means greatly decreased resistance to disease.
Undernutrition occurs almost exclusively in the context of poverty with its concomitants, which include: lack of opportunity to earn money; lack of land, or access only to land which yields little in relation to the labour and capital invested in it; lack of clean water; poor nutritional education; traditional food habits; low food quality; poor sanitation; limited access to medical and social services; and limited educational opportunities. All these problems are so closely linked that it is practically impossible to isolate the problem of undernutrition for an analysis of its causes and consequences and for the design of interventions which might improve the situation. In those cases where undernutrition is not a factor of poverty, depletion of vitamins is caused by taking drugs like the Pill and antibiotics, smoking cigarettes, drinking alcohol and eating faddish or vegetarian foods.
Diet consciousness, reaching proportions of hysteria in the western world, has ironically propelled a wave of vitamin and mineral deficiency among affluent young people, who may only recognize their dietary foolishness later in life.
Some kinds of junk food are not deleterious to health; it depends on age and on the general diet. A bag of potato crisps contains 140 calories and a lot of Vitamin C, and this may be a good snack for a child, who needs vitamins and energy, provided he eats a broad diet.