Delay in Renal Hemodynamic Response to a Meat Meal in Severe Obesity.

Background/aims: Little information is available about the tubular functions and the renal adjustments that take place in obese subjects after a protein meal. How the excess fat may affect renal response to dietary proteins is currently only partially understood. This paper aims to address (i) whether severe obesity, in the absence of other comorbidities, is responsible of kidney dysfunction at either the glomerular or the tubular level and (ii) whether it compromises renal adaptations to a large protein meal.

Methods: Twenty-eight obese subjects without albuminuria, along with 20 control subjects, age and gender matched, have been studied. The glomerular filtration rate (GFR; inulin clearance), renal plasma flow (p-aminohippurate clearance), the proximal tubular function (lithium clearance), the fractional excretion of sodium (FPRNa) have been measured at the basal level (steady state) and after a protein meal (perturbation).

Results: Under steady state conditions, filtration fraction, proximal tubular sodium handling and the FPRNa were not significantly different in non proteinuric obese subjects compared with controls. However, a protein meal led to a delayed glomerular hyperfiltration in obese patients compared with controls.

Conclusion: This study shows that obese patients, in the absence of significant comorbidities, have a normal proximal tubule Na+ absorption at basal; conversely, these subjects showed a different response to a protein meal compared with normal subjects in terms of changes of GFR. Overall, these results suggest that the modified hemodynamic response to a protein meal might be the earliest hallmark of future kidney dysfunction in obese subjects.