The intestinal fatty acid binding protein (FABP2) gene is proposed as a candidate gene for diabetes because the protein it codes is involved in fatty acid (FA) absorption and metabolism and may, therefore, affect insulin sensitivity and glucose metabolism. Numerous studies have assessed FABP2 gene variants and their association with insulin resistance and type 2 diabetes. Some weak evidence indicates that the silent variants and those in the noncoding regions of the gene (codon 118, 3' noncoding region, intron 2 trinucleotide repeat) might be associated with insulin resistance/type 2 diabetes. The most extensively studied variant is the missense Ala54Thr variation, which is common in diverse populations and results in increased FA absorption in vivo. Some evidence indicates that this variant may be associated with insulin sensitivity/type 2 diabetes. However, the large majority of studies assessing the potential association between the Ala54Thr FABP2 variant and insulin resistance/type 2 diabetes did not account for the independent and substantial effects of body composition, habitual physical activity (PA) levels, and diet on insulin resistance. We recently reported that there was an association between Ala54Thr FABP2 genotypes and insulin sensitivity after accounting for the independent effects of body composition and habitual PA levels on insulin sensitivity. Furthermore, others have demonstrated that Ala54Thr FABP2 may associate with insulin sensitivity, but only if individuals are consuming a high-fat diet. These results highlight the importance of including behavioral and environmental factors in the design of studies seeking to assess the impact of genes on physiological and clinical outcome phenotypes.