It will lose weight
The pyruvate is the product formed by the process of glycolysis by the breakdown of the glucose-mediated by enzymes.
The process of glycolysis take place in the cytosol therefore for further processing or stages of respiration, the pyruvate has to enter the mitochondria which occur through the (H+)/pyruvate symporter.
In the given question condition, if the symporter is blocked then the pyruvate will not enter into the mitochondria as a result of which less ATP will be produced. So the body will use some other sources which can form the pyruvate which can easily enter the mitochondria.
Therefore, the body will begin to lose weight.