Tolerance and the effects of caffeine mainly vary due to variants in the gene CYP1A2, responsible for its metabolism in the liver. Polymorphisms like rs762551 determine whether an individual is a fast or slow metabolizer of caffeine, which influences their sensitivity and its impact on sleep, blood pressure, and cognitive performance. Additionally, variants in ADORA2A can modulate the neurological response to caffeine, affecting the propensity to anxiety or tolerance to the stimulant.

The genotype HLA-DQ2 and/or HLA-DQ8 is associated with a genetic predisposition to celiac disease, while its absence significantly reduces the likelihood of developing this condition. The identification of these genetic markers allows for the assessment of risk and improves the customization of dietary strategies, facilitating a more accurate diagnosis.

Fasting glucose levels may be modulated by variants in genes such as TCF7L2 and GCK, which influence the regulation of glucose homeostasis. Polymorphisms in TCF7L2 have been associated with an increased predisposition to insulin resistance and the risk of type 2 diabetes, while variants in GCK may affect the pancreas's sensitivity to glucose levels. 

The genotype in variants of the gene AOC1 (DAO) may influence the ability to degrade histamine, which can increase the predisposition to intolerance to this biogenic amine. The variants that reduce the activity of the enzyme diamine oxidase (DAO) may favor the accumulation of histamine and trigger adverse symptoms.

The CC genotype at the SNP C/T_13910 indicates a high genetic predisposition to lactose intolerance, while the C/T or T/T genotypes indicate lactase persistence and thus a lower predisposition to this intolerance. Knowing this information allows for a personalization of guidelines and dietary treatments in professional consultation.