Pediatrics published a review of the research on thickened feeds for infants for at least 3 days and its effect on gastroesophageal reflux (GER).   The researchers concluded that thickened feeds are moderately effective in treating GER in infants.

Reference:  Horvath, Andrea, Dziechciarz, Piotr, Szajewska, Hania

The Effect of Thickened-Feed Interventions on Gastroesophageal Reflux in Infants: Systematic Review and Meta-analysis of Randomized, Controlled Trials

Pediatrics 2008 122: e1268-e1277