Final answer:
Type II diabetes is the most likely diagnosis for the symptoms described, as excessive urine production and obesity are typical indicators, and the patient's physician's advice aligns with diabetes management.
Step-by-step explanation:
The most likely diagnosis for a 30 year old obese woman experiencing polyuria and weight gain despite trying to lose weight is type II diabetes. This diagnosis is supported by her symptoms of excess urine production and weight gain, both of which are common in type II diabetes due to insulin resistance. Obesity is a significant risk factor for developing type II diabetes. Her physician's advice to watch what she eats if she becomes pregnant is consistent with managing blood glucose levels, which is crucial in diabetes care to prevent complications for both the mother and the developing fetus.
It's important to rule out other possible conditions such as type I diabetes, insulinoma, or ketoacidosis; however, the chronic weight gain rather than loss and polyuria without mention of other symptoms such as rapid breathing, nausea, or a fruity scent to the breath associated with ketoacidosis point more towards type II diabetes.