It is more difficult to meet nutritional needs during periods of increased requirements. Restricted range of foods . A diet based on a narrow range of foods is more likely to lack nutrients. For example poorly balanced slimming diets or vegetarian diets. Reduction in availability of food .
Famine is an extreme example.
Lack of money may make it difficult to purchase an adequate diet. Cultural practices may mean that not everyone in a family gets a fair share of the food available. Other substances in foods . Very high intakes of some substances, for example fibre, reduce absorption of some nutrients from food. Medical conditions .