Macropinocytosis is an actin-driven process of large-scale, non-specific fluid uptake used for feeding by some cancer cells and the macropinocytosis model organism Dictyostelium discoideum. In Dictyostelium, macropinocytic cups are organised by ‘macropinocytic patches’ in the plasma membrane. These contain activated Ras, Rac and PI(3,4,5)P3 and direct actin polymerisation to their periphery. Here, we show that a classical (PkbA) and a variant (PkbR1) Akt protein kinase acting downstream of PI(3,4,5)P3 are together are near-essential for fluid uptake. This pathway enables the formation of larger macropinocytic patches and macropinosomes, thereby dramatically increasing fluid uptake. Akt targets identified by phosphoproteomics were highly enriched in small G-protein regulators, including the RhoGAP GacG. GacG knockout mutants make few macropinosomes but instead redeploy their cytoskeleton from macropinocytosis to motility, moving rapidly but taking up little fluid. The function of Akt in cell feeding through control of macropinosome size has implications for cancer cell biology.