Hypocaloric Diet Prevents the Decrease in FGF21 Elicited by High Phosphorus Intake

The effect of dietary phosphorus (P) on fibroblast growth factor 21 (FGF21)/β-klotho axis was investigated in rats that were fed diets with: Normal (NP) or high P (HP) and either normal (NC), high (HC) or low calories (LC). Sampling was performed at 1, 4 and 7 months. Plasma FGF21 concentrations were higher (p < 0.05) in NC and HC than in LC groups. Increasing P intake had differing effects on plasma FGF21 in rats fed NC and HC vs. rats fed LC at the three sampling times. When compared with the NP groups, FGF21 concentrations decreased at the three sampling points in rats fed NC-HP (80 vs. 194, 185 vs. 382, 145 vs. 403 pg/mL) and HC-HP (90 vs. 190, 173 vs. 353, 94 vs. 434 pg/mL). However, FGF21 did not decrease in rats fed LC-HP (34 vs. 20, 332 vs. 164 and 155 vs. 81 pg/mL). In addition, LC groups had a much lower liver FGF21 messenger ribonucleic acid/glyceraldehyde 3-phosphate dehydrogenase (mRNA/GAPDH) ratio (0.51 ± 0.08 and 0.56 ± 0.07) than the NC-NP (0.97 ± 0.14) and HC-NP (0.97 ± 0.22) groups. Increasing P intake reduced liver FGF21 mRNA/GAPDH in rats fed NC and HC to 0.42 ± 0.05 and 0.37 ± 0.04. Liver β-klotho mRNA/GAPDH ratio was lower (p < 0.05) in LC groups (0.66 ± 0.06 and 0.59 ± 0.10) than in NC (1.09 ± 0.17 and 1.03 ± 0.14) and HC (1.19 ± 0.12 and 1.34 ± 0.19) groups. A reduction (p < 0.05) in β-klotho protein/α-tubulin ratio was also observed in LC groups (0.65 ± 0.05 and 0.49 ± 0.08) when compared with NC (1.12 ± 0.11 and 0.91 ± 0.11) and HC (0.93 ± 0.17 and 0.87 ± 0.09) groups. In conclusion β-klotho is potently regulated by caloric restriction but not by increasing P intake while FGF21 is regulated by both caloric restriction and increased P intake. Moreover, increased P intake has a differential effect on FGF21 in calorie repleted and calorie depleted rats.