This has been demonstrated in a variety of species: lambs offered free choice of various foods will compensate for phosphorus, sodium, and calcium deficiencies.
[2] Domestic fowl have demonstrated specific appetites for calcium, zinc, and phosphorus, thiamine, protein in general, and methionine and lysine.
Heat-stressed fowls seek out vitamin C, which alleviates the consequences of heat stress[3] Learned specific appetites are not necessarily a result of an animal's ability to detect the presence of a nutrient.
An unlearned appetite is one that an animal possesses at birth, without conditioning through prior stress followed by alleviation with specific foods.
In one study, normal (sodium-replete) rats exposed to angiotensin II via infusion directly into the brain developed a strong sodium appetite which persisted for months.
[14] While the most common nutritional disorders in humans concern excessive intake of calories, malnutrition remains a problem.
For example, the link between insufficient dietary calcium and bone disorders is well established[15] Commonly people have an appetite for meat or eggs, high protein foods.
Because protein is vitally important to maintaining the structures of the body’s systems, a form of protein-mediated hunger has been hypothesised.