GF Fiaf−/− mice are not protected against diet-induced obesity and have lower expression of Pgc-1α and genes involved in fatty acid oxidation in their gastrocnemius muscles. (A) qRT-PCR assays of Fiaf expression in the distal small intestines and livers of GF and conventionalized wild-type male mice maintained on a low-fat diet since weaning or given a high-fat Western diet for 8 weeks before being killed. Mean values ± SE are plotted. n = 5 mice per group. ∗∗, P < 0.01, compared with GF mice on the chow diet; Ψ, P < 0.05 compared with GF mice on the Western diet. (B) GF Fiaf-deficient mice become obese on a Western diet. Eight- to 10-week-old GF male wild-type and Fiaf−/− mice were switched to the Western diet and their body weights monitored weekly for 5 weeks (n = 5 per group). (C) Epididymal fat-pad weights of the mice shown in B after 5 weeks on the Western diet. (D) qRT-PCR assays of gastrocnemius muscle RNAs prepared from GF Fiaf−/− mice and wild-type littermates on the Western diet (n = 6 per group). Mean values ± SE are plotted. ∗, P < 0.05 compared with wild-type animals; ∗∗, P < 0.01.