A diagnosis of Avoidant/Restrictive Food Intake Disorder (ARFID) is indicated by:

A diagnosis of Avoidant/Restrictive Food Intake Disorder (ARFID) is characterized by marked interference with psychosocial functioning that is not better explained by another medical condition or psychological disorder. This disorder is primarily observed in the context of an individual's eating behavior that leads to significant nutritional deficiencies or impairment in functioning, such as difficulties in social interactions or maintaining health.

In this case, the correct identification of impairments in psychosocial functioning sets ARFID apart from other eating disorders, which may involve more complex interactions with body image and weight concerns. Recognizing that the eating patterns are not merely symptomatic of other conditions ensures appropriate diagnosis and treatment.

The other options do not capture the essence of ARFID accurately. Physical symptoms related only to food allergies focus on a medical issue rather than behavioral or psychological aspects of eating habits. Failure to achieve nutritional needs due to a lack of available food suggests a situational problem rather than the disorder's defining characteristics. Lastly, strict eating patterns due to cultural norms don't align with ARFID’s focus on the individual’s personal avoidance behaviors and their consequences on daily life. Thus, the correct understanding of ARFID is grounded in its significant impact on a person's functioning and the absence of an alternative explanation for these eating behaviors.