Phosphorus Supplementation Mitigated Food Intake and Growth of Rats Fed a Low-Protein Diet

Abstract

Background: Low protein intake is associated with various negative health outcomes at any life stage. When diets do not contain sufficient protein, phosphorus availability is compromised because proteins are the major sources of phosphorus. However, whether mineral phosphorus supplementation mitigates this problem is unknown, to our knowledge. Objective: Our goal was to determine the impact of dietary phosphorus supplementation on food intake, weight gain, energy efficiency, body composition, blood metabolites, and liver histology in rats fed a low-protein diet for 9 wk. Methods: Forty-nine 6-wk-old male Sprague-Dawley rats were randomly allocated to 5 groups and consumed 5 isocaloric diets ad libitum that varied only in protein (egg white) and phosphorus concentrations for 9 wk. The control group received a 20% protein diet with 0.3% P (NP-0.3P). The 4 other groups were fed a low-protein (10%) diet with a phosphorus concentration of 0.015%, 0.056%, 0.1%, or 0.3% (LP-0.3P). The rats' weight, body and liver composition, and plasma biomarkers were then assessed. Results: The addition of phosphorus to the low-protein diet significantly increased food intake, weight gain, and energy efficiency, which were similar among the groups that received 0.3% P (LP-0.3P and NP-0.3P) regardless of dietary protein content. In addition, phosphorus supplementation of low-protein diets reduced plasma urea nitrogen and increased total body protein content (defatted). Changes in food intake and efficiency, body weight and composition, and plasma urea concentration were highly pronounced at a dietary phosphorus content <0.1%, which may represent a critical threshold. Conclusions: The addition of phosphorus to low-protein diets improved growth measures in rats, mainly as a result of enhanced energy efficiency. A dietary phosphorus concentration of 0.3% mitigated detrimental effects of low-protein diets on growth parameters.

Keywords: Sprague-Dawley rats; energy efficiency; food intake; low-protein diet; nonalcoholic fatty liver disease; phosphorus; weight gain.

FIGURE 1

Mean daily weight gain (A), food intake (B), and energy efficiency (C) of rats fed a control diet or 1 of 4 low-protein diets with different phosphorus concentrations for 9 wk. Triangles indicate the control group (20% protein and 0.3% P). Circles indicate the 4 low-protein groups (10% protein with 0.015% P, 0.056% P, 0.1% P, or 0.3% P). Food intake, weight gain, and energy efficiency are expressed as means ± SDs as a function of the level of phosphorus in the diet (n = 9 or 10). Energy efficiency was calculated as the mean weight gained per day per 100 kcal of the corresponding diet consumed. One-factor ANOVA and specific comparisons were made between each of the 5 groups using Fisher's pairwise comparisons. Values that do not share the same superscript letter are significantly different (P < 0.05).

FIGURE 2

Plasma urea nitrogen concentrations (expressed in mM) of rats fed a control diet or 1 of 4 low-protein diets with different phosphorus concentrations for 9 wk. Triangles indicate the control group (20% protein and 0.3% P). Circles indicate the low-protein groups (10% protein with 0.015% P, 0.056% P, 0.1% P, or 0.3% P). The plasma urea nitrogen concentrations are expressed as means ± SDs as a function of the level of phosphorus in the diet (n = 9 or 10). One-factor ANOVA and specific comparisons were made between each of the 5 groups using Fisher's pairwise comparisons. Values that do not share the same superscript letter are significantly different (P < 0.05).