Effect of beef ingestion by humans on plasma concentrations of creatinine, urea, and cystatin C

The effect of eating meat on serum concentrations of creatinine has varied among previous reports, with some finding no effect and others finding 50–100% increases, which appears related to how the beef is cooked. For other analytes related to kidney function, urea is well known to increase following a protein meal, and the effect of eating meat on cystatin C concentrations has been studied once. We had 32 participants eat a measured amount of cooked beef (5–6 or 10–12 oz; 142–170 or 284–340 g) and collected blood for measurements at 1 h before and immediately before eating beef, then at 1, 2, and 4 h after eating the beef. We measured creatinine using both alkaline picrate and enzymatic methods, cystatin C using a nephelometric immunoassay, and urea using an enzymatic method. For creatinine, both the picrate and enzymatic methods showed similar responses, with a peak average increases of 5.9 μmol/L (0.07 mg/dL) and 4.6 μmol/L (0.05 mg/dL), respectively, at 2 h. Cystatin C had a very slightly maximal decrease of −0.037 mg/L at 2 h. Urea had the largest change, increasing by 0.30 and 0.77 mmol/L at 2 and 4 h respectively. Healthy individuals were found to have minor increases in serum creatinine (~5 μmol/L) following the ingestion of 5/6 or 10/12 oz of fried beef. Cystatin C appears to decrease very slightly in some people after beef ingestion, possibly due either to circadian variation or to a hormonal effect of eating. We conclude that ingesting these amounts of fried beef has a small effect on plasma creatinine concentrations. Although these increases would likely not affect the diagnosis of a kidney impairment in this population or in those with kidney disease, eating meat before collecting blood for creatinine measurement should be avoided.