Final answer:
John likely has anosmia, a lack of the sense of smell, which makes food taste bland because smell is crucial to experiencing the full range of complex flavors in food. Enhancing food with certain ingredients can improve perceived taste despite impaired olfaction.
Step-by-step explanation:
If John is only able to detect the primary tastes of sweet, salty, sour, and bitter without the complexities, it is likely that he may be experiencing a reduced sense of smell rather than a taste disorder. A severe reduction in the ability to smell is known as anosmia. The enjoyment and complexity of food's flavor largely depend on our sense of smell. Smell and taste are closely related, and when one's olfaction is impaired, food may taste bland since the olfactory sense is integral to detecting the full range of flavors beyond the basic tastes. Adding compounds such as salt or monosodium glutamate can stimulate the gustatory sense, enhancing the taste experience even when the sense of smell is not functioning properly. Umami, identified as the taste of the amino acid L-glutamate, and possibly a sixth taste for fats, enrich the flavor experience beyond the five cardinal tastes which includes umami as well as sweet, sour, salty, and bitter. Therefore, John's perception of meals as bland could indicate a problem with his sense of smell, not solely his taste receptors.