Hey , A loss of penis length associated with weight gain may be purely a visual effect: because there is more fat in the pubic area, including abdominal fat that exerts weight and pressure on the scrotum, the penis may appear to be shorter even though it physically is not. However, being overweight or obese also increases the risk of poor blood flow to the penis and cause men to have difficulty achieving sufficient rigidity. So take required measures to reduce weight like exercise, yoga etcc..