Acts as an electroneutral and low-affinity sodium (Na(+))-dependent sodium-coupled solute transporter. Catalyzes the transport across the plasma membrane of many monocarboxylates such as lactate, pyruvate, nicotinate, propionate, butyrate and beta-D-hydroxybutyrate. May be responsible for the first step of reabsorption of monocarboxylates from the lumen of the proximal tubule of the kidney and the small intestine. May play also a role in monocarboxylates transport in the retina. Mediates electroneutral uptake of lactate, with a stoichiometry of 2 Na(+) for each lactate (By similarity). Detected at the brush border membrane of the kidney. Colocalizes with viementin in Mueller cells (By similarity). Belongs to the sodium:solute symporter (SSF) (TC 2.A.21) family.