A person can weigh 2 to 3 pounds less in the morning because the body loses some weight overnight. Weight loss is attributed to the removal of excess fluids from the body, including urinating in the morning and sweat that evaporates into the air.
The lungs also release carbon dioxide and water vapor as a result of the body converting food to energy. A person can lose about 2.5 to 7 quarts of water per day, which is equivalent to 6 to 15 pounds. If just one-third of this water loss happens overnight, that accounts for the possible 2 to 3 pounds difference in weight in the morning compared to the night before.