The reasons not to give a certain nutritional product to a person of a certain age are as follows.
1. The product might provide too much a nutrient to the individual, this is usually only a concern in very young children, children less than 6 mo of age.
2. The product is used to replace or constitute the majority of a habitual diet, rather than add to the diet. To replace a a substantial portion of the diet, minimum adequate amounts of several nutrients must be present. Ready-to-use therapeutic food in severe acute malnutrition is an example of a product constituting the majority of a diet.
3. The population in which the product is to be used has special needs, often because of the presence of certain diseases. An example is, people with renal failure cannot excrete micronutrients as well as those with normal kidneys, and require products with less potassium.
Plumpy Doz, is peanut paste with micronutrients appropriate for children under 5 years. Plumpy Doz can be safely given to anyone over the age of 6 mo for malnutrition prevention.
The use of Plumpy Doz in prevention is not the type of question that requires scientific studies, and therefore I do not have such to offer you. In children over 2 years and the presence of marked food insecurity, one sachet of Plumpy Doz might not be enough to prevent malnutrition. A ration of another food might be needed.