Gerald has restricted his calorie intake while continuing to exercise, and has been losing 1.5 pounds per week. However, when he weighs himself at the end of week 4, he notices he has not lost any weight since last week. What does this likely mean?

It means Gerald's body retains water while it burned fat.

Explanation:

Calorie intake affects how our body burns stored and burn fat and also how much calories are utilized. Weight loss becomes very effective when calories and fat are utilized by low-calorie intake and exercising.

Our bodies store fat in the fat cell and they remain inactive until it is needed by the body. The body makes use of the calories for energy production of its day to day activities. When there is low-calorie intake and physical activities such as exercising are carried out, the fat in the fat cell provides energy. This utilization of the fat leads to fat burning resulting in weight loss.

Gerald restricted his calorie intake while involving in exercising, it resulted in weight loss for 3 weeks. At the end of the fourth week, it is also expected that the Gerald will burn fat which he did, but his body retained water.

The water retained by Gerald's body accounted for the fat that was burned thus there was no weight loss.