What primarily determines the onset of nutritional disease?

The correct answer is based on the understanding that the onset of nutritional disease is significantly influenced by the levels of nutrient reserves in tissues. Nutritional diseases often arise when the body’s nutrient reserves—such as vitamins, minerals, and macro-nutrients—are depleted or insufficient to meet physiological needs. These reserves play a critical role in maintaining overall health, and when they are low, various deficiencies can occur, leading to a range of health issues.

For instance, if the body does not have adequate reserves of vitamin D, it may lead to conditions like rickets or osteomalacia. Similarly, a lack of iron reserves can result in anemia. Thus, the levels of nutrient reserves directly correlate with the body's ability to function optimally and defend against diseases.

In contrast, while the amount of food intake is vital for providing nutrients, it is not solely indicative of a person’s nutritional status, as the body may not effectively utilize all consumed nutrients. The body's ability to react to infections is more related to the immune system rather than directly to nutritional health, although nutrition can support immune function. Individual idiosyncrasies—such as genetic predispositions—can influence nutritional needs but do not primarily dictate the onset of nutritional diseases. Therefore, the focus on